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Practical Nutrition for Clinicians

Practical Nutrition for Clinicians

Introduction

Clinical practitioners need to know about nutrition because research and experience show that proper nutritional care can reduce medical complications, speed healing, and improve outcome in sick people. In the hospital, clinical dietitians are taking an increasingly proactive role in planning and executing treatment regimens. Doctors now routinely order nutrition assessments and seek advice on formulas, diets and supplementation; pharmacists, respiratory therapists, nurses, social workers and kitchen workers all come into contact with nutrition terminology and concepts every day. In short, a working knowledge of nutrition—or at least familiarity with its basic concepts and terminology—is essential to participation in a health care team.

Outside the hospital, such knowledge is even more critical. In many cases, Medical Assistants, Physician Assistants, nurses and Nurse Practitioners serve “gatekeeper” functions. In that role, they’re often in the best position to identify and refer potentially serious nutritional problems to specialists. In less-serious cases, these practitioners can and should have confidence to recommend dietary modifications. These activities require a level of competence in understanding nutrition principles and practice.

Unfortunately, many health professionals have little formal training in nutrition, and their understanding of the ever-changing research in high-end clinical nutrition rapidly becomes dated. Worse, many have formed erroneous opinions and beliefs from folklore, media misreporting and pseudo-scientific marketing hype for nutritional products. Add to this the natural division of responsibility in a health care setting, and you have a recipe for misunderstanding. Seldom do members of different professions fully understand another professional’s concerns, priorities and pressures.

So, let’s try to change that. The first goal of this course is to help you understand basic principles and terminology and enable you to apply this knowledge in a clinical setting.

Nutrition is defined as “The act or process of nourishing or of being nourished” and “The sum of the processes by which animals or plants take in and utilize food substances.” That’s a useful concept: the sum of the processes . . . . In more than 20 years of practice, I’ve learned that there is a psychological component to nutrition. While this is not a psychology course, it is important to note that people become attached to their diet patterns and sometimes form irrational belief systems about nutrition. As a clinician, you have to deal with emotions as well as physiology and biochemistry.

Nutrition, for many people, is a realm of confusion, quackery and pseudo-science. This course will help you recognize misinformation when you see it. Knowing how carbohydrates and proteins really work, for example, will help you dispute “miracle diet” claims, or recognize the grain of falsehood in advertising for a supplement. You could help someone abandon a harmful nutrition practice.

To do this, we need to start with just a bit of science. Nutrition involves chemistry, biochemistry and physiology. I’ll explain how cells use nutrients and how digestion and absorption work, and define some common nutrition terminology. I’ll explain how common diet-related conditions develop, because nutrition and diet modification can have a profound effect. I’ll give you a short course on nutrition assessment techniques—not to turn you into a clinical dietitian, but to enable you to understand how a clinical dietitian works, and why the information is needed.

Throughout the course, I’ll offer exercises and drills to test your understanding of the material and to allow you to personalize the information in the chapters. These are not mandatory for credit, but they will certainly help you understand the concepts being presented, so I urge you to complete them.

In the four years since the first edition of this course was published, I have been gratified to receive many positive comments and constructive suggestions. I’ve tried to incorporate and account for this valuable feedback. I’d like to acknowledge and thank all those people who have helped me refine and improve this second edition.

CHAPTER ONE: THE PROBLEM

Why is nutrition so important? Aren’t we overstating the case somewhat? Hasn’t humanity been doing OK without knowing about cholesterol, dietary fats, vitamins and minerals? Aren’t fad diets and arcane supplements, at worst, a harmless diversion, like fortune telling or numerology? Doesn’t medical science cure most things with drugs and/or surgery, no matter what we eat while in the hospital? Didn’t our ancestors eat pretty much what they wanted and live to ripe old ages?

Simply, no. We haven’t been doing all that well. Oh, we’re living longer—although the mortality statistics may be skewed somewhat by significant improvement in infant mortality and deaths in childbirth, as well as end-stage treatments which prolong life—but we may not be living better.

People do get well in hospitals, but they may not be getting well fast enough. We’re much more likely now to develop some diseases that are incapacitating and life-threatening—diseases which are diet- and lifestyle-related, and, therefore, preventable.

Look at the leading causes of death in 1900 and 1995, shown in the chart on the following page.

In 1900, the number one cause of death was pneumonia, an infectious disease. In 1983, and today, it’s heart disease. People aren’t dying of infectious diseases like tuberculosis, diarrhea or enteritis because we’ve developed effective antibiotics and other medical treatments.

Instead, they’re dying from heart disease and cancer: 62 percent of the deaths every year are from a degenerative disease that has a relationship to diet and lifestyle. If you add cerebrovascular disease (stroke) you get nearly seven out of 10 deaths from diet-related diseases.

About 800,000 people die every year from heart disease in the United States. More than 35 million Americans have hypertension, or high blood pressure. Ten million have diabetes.

(And these are probably low estimates, because a lot of people may have these diseases and not necessarily know it. People who complain of being tired, of not having a lot of energy, of gaining or losing weight may not know that they have diabetes. They don’t really know they have hypertension until they’ve had their blood pressure checked.)

Forty percent of all Americans are overweight. Overweight and/or obesity is the number one nutritional disease in the United States, and overweight or obesity is linked with all the diseases just mentioned.

The chart on the following page shows how the typical American diet promotes disease. In generally Americans eat a diet too high in cholesterol, fats, salt and calories, and too low in fiber. You can see some of the problems that this kind of diet causes in everyday life.

In recent years we’ve seen a lot of reports and studies implicating diet in illness. The U.S. Surgeon General, the American Cancer Society, the American Heart Association have all issued reports and recommendations. All of them have noted that our dietary habits cause health problems.

Sometimes these reports can seem contradictory and confusing, particularly when researchers start splitting hairs and advertisers start distorting research information to sell products. But as you can see in the chart below (summarized from the Surgeon General’s 1988 Report on Nutrition and Health), all of the diseases we’ve mentioned can be minimized and controlled through relatively simple dietary modifications.

So the health of the general population can be improved through nutrition. But what about the hospital patient? Especially one whose lifetime of bad nutrition habits have placed him at increased risk for complications and, perhaps, impaired his immune system? What happens when a marginally malnourished person has a serious illness requiring hospitalization, surgery, chemotherapy?

Hospital Malnutrition

About two decades ago, the issue of malnutrition in hospitalized patients first came to the forefront. A physician, Charles Butterworth, in a landmark article called The Skeleton in the Hospital Closet, noted that “malnutrition is a common accompaniment to the stress of illness among hospitalized patients. . . undoubtedly contributing to increased mortality and morbidity.”

The incidence of malnutrition in hospitalized patients has been estimated at one out of every five patients, with the incidence increasing to almost 50 percent of patients who have been hospitalized for a longer period of time.

Nutrition status may worsen in the hospital because of the lack of adequate nutritional support, but the root causes are often procedural, as Butterworth’s 1974 paper summarized.

Causes of Hospital Malnutrition

  • Failure to record height and weight
  • Prolonged glucose, saline IV feedings
  • Failure to observe food intake
  • Withholding meals because of tests
  • Unrecognized increased needs due to injury or illness
  • Delayed or inadequate nutrition support

“Failure to record height and weight,” “prolonged glucose and saline intravenous feedings,” “failure to observe intake,” “withholding meals because of tests,” “failure to recognize increased nutritional needs until the patient is in an advanced state of depletion.” Do any of these sound familiar?

Significant instances of three types of malnutrition have been recognized in hospitalized patients: marasmus, kwashiorkor and protein-calorie depletion.

Marasmus Many people understand malnutrition as starvation, familiar in third world nations. You know the sight: the child from Somalia who is all skin and bones except for his distended abdomen. This child could be diagnosed as having marasmus, or caloric depletion. Marasmus occurs when a person does not consume adequate amounts of calories and protein, usually because of fasting or starvation.

Marasmus Appearance/anthropometric symptoms

  • Diminished skinfold thickness
  • Reduced arm circumference
  • Starved appearancee
  • Weight 80% or less of Ideal Body Weight

Physiological symptoms

  • Decreased protein stores o in somatic and gut masses o visceral protein stores conserved
  • Diminished fat stores, glycogen, muscle mass
  • Enzymes, plasma proteins normal

During any fasting, and with marasmus, the decrease in protein stores occurs mostly in the somatic and gut masses, while visceral protein stores usually are conserved. Thus, the patient becomes wasted, with diminished stores of fat, glycogen and muscle mass. However, enzymes, plasma proteins (such as albumin) and immune function appear to remain normal. If starvation continues for an extended period, however, even visceral protein stores will be utilized for energy to maintain body functions, and the person is at increased risk for infection and death. In the hospital setting, marasmus generally occurs in the patient receiving inadequate calories. He will appear starved, and his weight will be about 80 percent of ideal body weight.

We have all been exposed to pictures of third world residents with marasmus, but few of us have seen it in actual practice. Why should we, then, be concerned with marasmus in our patients?

To answer that question, I’ll ask some more: How many patients have you seen being left without oral intake, enteral feedings or total parenteral nutrition for an extended period of time? How many have you seen receive as their total nutritional support only a liter of D10 formula per day? How many of your patients have been on a “regular” diet during their entire hospital stay, but have not been able or willing to eat all of it, and go home having lost 10 to 20 pounds?

Clearly, even subclinical marasmus is of concern. Generally, patients with marasmus respond to adequate feeding, and bad effects are easily overcome.

Kwashiorkor Another type of malnutrition is kwashiorkor, also known as protein depletion. Kwashiorkor occurs when a person has an adequate intake of calories from fat and carbohydrate, but inadequate intake of protein. The person with kwashiorkor may not look ill-nourished—in fact, he or she may even be obese.

Many elderly people may be at risk for kwashiorkor because of their diminished ability to consume high protein foods. We’ve all come across the elderly woman who lives on tea, toast and jam. She may appear well nourished (and may even be overweight) but her protein stores will be well below normal.

Kwashiorkor Appearance/anthropometric

  • May look well-nourished, even obese
  • Common in elderly population

Physiological symptoms

  • Greater protein synthesis, catabolism, sparing
  • Liver produces acute phase proteins such as fibrinogen
  • Protein conserved in somatic compartment
  • Low lymphocyte count
  • Low serum albumin
  • Low serum transferrin

As with marasmus, the body adapts to inadequate protein intake with changes in hormonal interactions that affect all systems of the body, especially liver functions. Thus, a person with kwashiorkor is often more ill and at greater risk for infection and death than a person with marasmus, since immune function decreases and risk for morbidity and mortality increases.

With severe protein depletion, intestinal and gastric absorption is impaired because of a diminished production of gastric, pancreatic and bile juices. The ability to carry medications, minerals, hormones and other substances usually transported through the blood on protein will also be altered.

Kwashiorkor typically occurs in the patient who has had a history of low protein intake and an increase in stress from surgery, sepsis, trauma, etc. Wound healing is hindered and he or she is at increased risk for opportunistic infections.

Feeding a patient with only a dextrose infusion—the typical D10 formula is mostly dextrose—will worsen a developing case of kwashiorkor. The feeding of carbohydrate without protein causes a breakdown in the normal adaptation of the body to starvation.

Protein calorie malnutrition A combination of marasmus and kwashiorkor is called protein calorie malnutrition (PCM), or protein energy malnutrition. It is important to identify the incidence of PCM in hospitalized patients, since with a loss of only 20 percent of body protein and/or calories, physiological functions will be impaired.

Identifying Risk Factors

Who is at greatest risk for developing malnutrition before, during, or after hospitalization? From a variety of sources, we have identified those at risk, as summarized below.

Risk Factors for Malnutrition Weight abnormalities

  • Underweight (<80% of standard)
  • Overweight (>120% of standard)
  • Losses >10% of usual weight

Impaired intake

  • No nutrition support
  • No oral intake > 5-7 days
  • Alcoholism

Abnormal losses

  • Malabsorption, fistulas, dialysis, wounds

Increased needs

  • Sepsis, trauma, major surgery, burns or fever

Medication

  • Steroids, immunosuppressants, antineoplastic agents

The patient may be underweight (at less than 80 percent of standard) or overweight (greater than 120 percent of standard). He may have lost more than 10 percent of usual body weight. He may be an alcoholic. The patient may have been without nutrition support and any oral intake for greater than 5 to 7 days.

The patient who has greater than normal nutrient losses from malabsorption, fistulas, dialysis, wounds, etc. is at greater risk for development of protein malnutrition or protein calorie malnutrition. Also at risk are those patients with sepsis, trauma, major surgery, burns or fever, and those patients who are administered medications such as steroids and immunosuppressants.

We’ve come a long way since 1974, when “the skeleton in the hospital closet” was first identified. In 1988, an evaluation of patients was repeated, utilizing the same parameters as the ones used by Butterworth.

This study indicated that the incidence of malnutrition during hospitalization had decreased. However, if the patient was hospitalized for a longer period of time, he continued to be at risk—to the same degree as in 1974—for the development of malnutrition. In fact, 45 percent of malnourished patients are hospitalized longer than the average. Butterworth, in 1974, concluded that “. . . early recognition and treatment of nutritional depletion may decrease the length of stay . . . of malnourished patients.”It appears his insight is still valid today.

CHAPTER TWO: CELLS AND SYSTEMS

To understand nutrition, we need to understand the cell. The first consideration in nutrition is always “What does the cell need to survive?” because the body is made up of billions of cells. Each cell is performing its work all the time, every day. Each cell has a life span and will be replaced when it dies. (Although as we get older not all cells are replaced).

It takes a lot of energy—what we call "calories"—for cells to do their work. It also means that the material the cells need to work must be replenished in other words, the cell has to have building materials available. These materials we call “nutrients.”

Functions of a Cell

  • Perform work
  • Maintain itself (rebuild/repair)
  • Reproduce
  • Process materials needed to perform its work
  • Produce regulatory substances (e.g.hormones)

The picture above represents a typical cell.

Although cells have unique functions heart cells are different from kidney cells, for instance they all have certain activities and functions in common.

The Cell

The primary function of any cell is to “perform work,” whatever the task of the organ or tissue it’s in might be. Cells can repair some damage to themselves and they reproduce, divide and form new cells all the time. They also process materials needed to do work: a cell can take in substances and do something with them.

The body’s functions are regulated by chemicals (some are called hormones), which the cells can produce. These regulatory substances basically tell cells what to do, when to do it, and when to stop doing it. Also, cells must clear waste products. When you utilize energy, you make waste; just as when you burn gasoline in a car, you produce exhaust gases that are expelled.

Nutrient Needs of a Cell

  • Energy to burn for fuel
  • Oxygen to burn the fuel
  • Water for chemical processes
  • Materials to build and repair itself (protein, carbohydrates, etc.)
  • Vitamins & minerals to perform its functions

For all these functions, cells need nutrients. Cells need calories to burn for fuel and oxygen to burn the calories. To get oxygen to the cells, the body needs iron to make red blood cells. Cells need water—in fact, the body is made up of lots of water. If you lose only three percent of your total body water, you’re not able to perform properly. Athletes who become dehydrated do not perform as well—their muscles cramp and lose strength.

Cells need the materials to build and repair themselves. A cell is enclosed in a membrane which lets some substances enter and leave. The membrane is made up of proteins, fats and carbohydrates. So the things we eat become part of the cell membrane. A picture of a membrane is shown below.

Cell Membrane Structure

Besides these structural nutrients, cells need vitamins and minerals to perform their functions. These nutrients—water, carbohydrates, fats, proteins, vitamins and minerals are—called “essential nutrients.”

The definition of essential nutrients is “Nutrients that can’t be synthesized by the body in amounts necessary to meet its needs.” Either the body doesn’t make any, or doesn’t make enough, for the cells to use to perform their functions. Another definition is “Nutrients necessary for life that the body cannot make for itself.”

For example, the human body doesn’t make vitamin C. Dogs and monkeys make vitamin C—they have an enzyme in their bodies that converts certain chemicals to vitamin C. Our bodies do not have that enzyme so we have to get vitamin C from the foods we eat.

Our bodies do not make all the amino acids we need for protein, so we need to eat protein. If we don’t get enough essential nutrients from food, the body becomes deficient, which interferes with the cells’ ability to work, causing problems. The bigger the deficiency, the bigger the problem.

By the way, when we look at a list of essential nutrients, what’s missing? Cholesterol. Cholesterol is not an essential nutrient. If we never ate one milligram of cholesterol, our body would still make all we need. We just happen to like foods that have a lot of saturated fats—and for that reason we experience unhealthy levels of cholesterol which lead to circulatory diseases. This is an example of how excesses in our diet can be just as harmful as deficiencies.

In our country we don’t see a lot of what are called clinical deficiencies, except in extremely ill patients whose bodies have stopped utilizing nutrients made available to them or who are unable to ingest enough nutrients. Such things as beri-beri (a deficiency of thiamine), pellagra (niacin deficiency), and scurvy (vitamin C deficiency) are rare in the general population. But we see marginal deficiencies all the time, and must try to determine what missing nutrients interfere with function and produce ill health.

There is, of course, an ongoing debate in the dietetic and medical community over what levels of which nutrients you need and new research is constantly emerging to modify what we understand as the correct nutritional balance. It’s not the intent of this course to evaluate each and every argument about nutrition and health but rather to provide a basis of information so you understand the body’s needs and functions, insofar as nutrition is concerned. Later chapters will deal with special requirements, supplements and similar issues.

Organ Systems

Organs in the body are made up of tissues, which are a collection of cells specialized to perform certain functions. As you saw earlier, all cells perform work, much of it the same regardless of the tissue they are in—produce energy, clear waste, reproduce, etc. When a cell is part of a tissue in an organ system, it may have functions different from other cells. Shown on the next page is a list of organ systems and the functions they perform.

To perform work, all cells need certain things: oxygen to burn fuel for energy; water to regulate body temperature and carry vital substances; and vitamins, minerals and macronutrients (see page 11) to enable and regulate functions and as the building blocks of cells.

Systems & Functions Skeletal Support body; store calcium Muscular Perform work Nervous Transmit information Endocrine Produce regulatory hormones Respiratory Gather oxygen; expel waste gases Circulatory Transport oxygen, nutrients Lymphatic Transport water, waste; immune functions Digestive Break down foods into nutrients/absorb nutrients Excretory Expel solid, liquid wastes Reproductive Perpetuate species Immune Fight harmful “invaders”, protect the host

As you can see from the diagram on the next page, organ systems work together to control all the functions of the body. The digestive system digests and absorbs nutrients which the heart pumps via the bloodstream to the cells. As the blood passes through the lungs, oxygen is added to it and carbon dioxide is removed. The heart also pumps blood to the kidneys which filter and remove other waste products of the body. The immune system attacks invaders to keep the body alive and healthy.

What happens if one or more of the systems are not functioning properly? The body gets sick. The problem may be caused by a nutritional deficiency or from a disease. But whatever the reason for the breakdown, the body is impaired. Unfortunately, the breakdown in one system usually affects other systems as well.

In diabetes, the pancreas produces insufficient insulin—a hormone. Insulin is responsible for getting sugar (glucose) from the blood into the cell, where it is burned for energy. Without insulin, the sugar stays in the blood and begins to build up. The excess sugar in the blood can harm the arteries and veins, the eyes and the kidneys. While the original problem was hormonal (not enough insulin), untreated, the problem spreads to the eyes, circulatory system and excretory system, causing damage to these organs and organ systems.

The chart below shows how a disease of one organ system affects others.

Systemic Breakdowns Disease Primary System Also affects Diabetes Endocrine system Decreases energy available to cells of all organs Hypertension Circulatory system Impairs delivery of nutrients, removal of waste from all organs (especially impairs kidneys, heart) Bowel Disease Digestive system Decreases nutrients available to all cells, tissues, organs Atherosclerosis Cardiovascular system Decreases blood supply to the heart, brain, and periphery. Causes heart attacks, strokes, decreased circulation

High blood pressure, discussed in more detail in a later chapter, decreases the ability of the heart to pump blood through veins and arteries. This can cause a decrease in the nutrients delivered to the cells and cause less blood to flow to the kidneys, decreasing their function.

Diseases of the bowel—Crohn’s, inflammatory bowel disease, celiac sprue, etc. —interfere with the intestines’ ability to absorb nutrients. Therefore, fewer nutrients are being taken into the body, and fewer nutrients are available to the cells. Depending upon the severity of the disease, the decrease in nutrients may be small or large.

Providing cells with proper nutrients is critical to their functioning. It prevents system breakdowns that are caused by lack of nutrients. Unfortunately, eating well and having adequate nutrients may not always prevent diseases caused by factors other than diet and nutrition.

Macronutrients

An essential concept in nutrition is macronutrients carbohydrates, proteins and fats. “Macro” means “large”; you need large amounts of them, compared to micronutrients, such as vitamins and minerals, which are required in much smaller amounts.

Macronutrients CARBOHYDRATES, PROTEINS, FATS

  • “Calorie Carriers” are burned for energy
  • Contain vitamins/minerals
  • v Have specific functions in the body
  • Are essential in the diet

We call macronutrients “calorie carriers” because all of the calories in our diet come from these three substances.

These macronutrients are what the cells burn for energy. A “calorie” is the unit of measure for energy. How many calories a person needs to eat in a day is determined by the energy needs of every cell in the body. As you will see later, each macronutrient has functions in the body besides providing energy. Carbohydrates are part of the cell membranes (albeit a minor part), proteins are the building blocks of all cells, fats are the basis of specific regulatory substances. Foods that contain macronutrients also contain vitamins and minerals.

This is an important point: vitamins and minerals do not provide energy. They are necessary in the process that makes energy, but they are not the substance the body “burns”. Many people think “If I take a supplement with B vitamins, I’ll have more energy.” But B vitamins don’t make energy; they are important to help you burn carbohydrates for energy, but there’s no energy in any vitamin or mineral.

We get energy only from macronutrients—carbohydrates, proteins, and fats—and they are found only in food. If you do not have enough vitamins and minerals, they will interfere with energy production. But more vitamins and minerals will not increase energy production. The diagram below shows that food is the source of all nutrients needed by the body.

Energy Production

The drawing below illustrates how the macronutrients provide energy. The body loves to make energy out of carbohydrates; they are the preferred source of energy. You can see why: the body converts carbohydrates directly into a substance called glucose. You’ve heard of “blood sugar”; blood sugar means glucose. Glucose is easily burned by the cells.

Dietary fat is the body’s second preference as an energy source. The body takes fat, breaks it down into fatty acids, and burns that for energy.

Protein is the third preference. The body would rather use amino acids, the components of protein, as building blocks to make cells but it will convert some amino acids to glucose and then burn the glucose for energy. Neither proteins nor amino acids are burned directly for energy; they must be first converted to glucose.

It’s amazing that the body can completely transform one kind of nutrient into another. This is for survival. If you are starving, your body first exhausts its blood sugar, then begins to use its fat stores. To prevent too much fat loss, the body will begin to break down cells and utilize the proteins in them as energy.

Starving people appear to “waste away”; their muscles are broken down to produce energy for their organs, and their fat stores are depleted. The body will decrease its need for calories by reducing the rate it burns energy. These changes are one reason people can exist on very little food for extended periods of time. We’ve all seen pictures of captives or castaways who existed for weeks without food. Their bodies converted muscle tissue protein into glucose to allow their brain and heart to function.

In World War II, a group of conscientious objectors volunteered to serve as guinea pigs in a study to see what would happen to the body when it didn’t have enough calories and nutrients. They found that the body primarily burns stored fat if it isn’t getting enough carbohydrates, but the brain and the heart still need glucose, so the body breaks down its own muscle tissue to provide glucose.

Remember, the heart is muscle, so a starving body can break down its own heart muscle to get amino acids to convert to glucose for energy. That’s one hazard of very low calorie diets.

When liquid diets first came out about 20 years ago, some people became deficient in carbohydrates. To keep their hearts and brains functioning, their bodies had to break down muscle to convert it to glucose for the heart and brain. There were deaths, both during the weight loss and after they began eating normally again, presumably from the loss of heart muscle (to make energy) and possible loss of minerals.

Of course, starvation isn’t our main health problem. Rather, it’s the opposite. Any excess glucose, fat or protein is stored as fat in the body.

In the next chapters, we’ll look more closely at these macronutrients.

Although cells have unique functions heart cells are different from kidney cells, for instance they all have certain activities and functions in common.

The Cell

The primary function of any cell is to “perform work,” whatever the task of the organ or tissue it’s in might be. Cells can repair some damage to themselves and they reproduce, divide and form new cells all the time. They also process materials needed to do work: a cell can take in substances and do something with them.

The body’s functions are regulated by chemicals (some are called hormones), which the cells can produce. These regulatory substances basically tell cells what to do, when to do it, and when to stop doing it. Also, cells must clear waste products. When you utilize energy, you make waste; just as when you burn gasoline in a car, you produce exhaust gases that are expelled.

Nutrient Needs of a Cell

  • Energy to burn for fuel
  • Oxygen to burn the fuel
  • Water for chemical processes
  • Materials to build and repair itself (protein, carbohydrates, etc.)
  • Vitamins & minerals to perform its functions

For all these functions, cells need nutrients. Cells need calories to burn for fuel and oxygen to burn the calories. To get oxygen to the cells, the body needs iron to make red blood cells. Cells need water—in fact, the body is made up of lots of water. If you lose only three percent of your total body water, you’re not able to perform properly. Athletes who become dehydrated do not perform as well—their muscles cramp and lose strength.

Cells need the materials to build and repair themselves. A cell is enclosed in a membrane which lets some substances enter and leave. The membrane is made up of proteins, fats and carbohydrates. So the things we eat become part of the cell membrane. A picture of a membrane is shown below.

Cell Membrane Structure

Besides these structural nutrients, cells need vitamins and minerals to perform their functions. These nutrients—water, carbohydrates, fats, proteins, vitamins and minerals are—called “essential nutrients.”

The definition of essential nutrients is “Nutrients that can’t be synthesized by the body in amounts necessary to meet its needs.” Either the body doesn’t make any, or doesn’t make enough, for the cells to use to perform their functions. Another definition is “Nutrients necessary for life that the body cannot make for itself.”

For example, the human body doesn’t make vitamin C. Dogs and monkeys make vitamin C—they have an enzyme in their bodies that converts certain chemicals to vitamin C. Our bodies do not have that enzyme so we have to get vitamin C from the foods we eat.

Our bodies do not make all the amino acids we need for protein, so we need to eat protein. If we don’t get enough essential nutrients from food, the body becomes deficient, which interferes with the cells’ ability to work, causing problems. The bigger the deficiency, the bigger the problem.

By the way, when we look at a list of essential nutrients, what’s missing? Cholesterol. Cholesterol is not an essential nutrient. If we never ate one milligram of cholesterol, our body would still make all we need. We just happen to like foods that have a lot of saturated fats—and for that reason we experience unhealthy levels of cholesterol which lead to circulatory diseases. This is an example of how excesses in our diet can be just as harmful as deficiencies.

In our country we don’t see a lot of what are called clinical deficiencies, except in extremely ill patients whose bodies have stopped utilizing nutrients made available to them or who are unable to ingest enough nutrients. Such things as beri-beri (a deficiency of thiamine), pellagra (niacin deficiency), and scurvy (vitamin C deficiency) are rare in the general population. But we see marginal deficiencies all the time, and must try to determine what missing nutrients interfere with function and produce ill health.

There is, of course, an ongoing debate in the dietetic and medical community over what levels of which nutrients you need and new research is constantly emerging to modify what we understand as the correct nutritional balance. It’s not the intent of this course to evaluate each and every argument about nutrition and health but rather to provide a basis of information so you understand the body’s needs and functions, insofar as nutrition is concerned. Later chapters will deal with special requirements, supplements and similar issues.

Organ Systems

Organs in the body are made up of tissues, which are a collection of cells specialized to perform certain functions. As you saw earlier, all cells perform work, much of it the same regardless of the tissue they are in—produce energy, clear waste, reproduce, etc. When a cell is part of a tissue in an organ system, it may have functions different from other cells. Shown on the next page is a list of organ systems and the functions they perform.

To perform work, all cells need certain things: oxygen to burn fuel for energy; water to regulate body temperature and carry vital substances; and vitamins, minerals and macronutrients (see page 11) to enable and regulate functions and as the building blocks of cells.

Systems & Functions

As you can see from the diagram on the next page, organ systems work together to control all the functions of the body. The digestive system digests and absorbs nutrients which the heart pumps via the bloodstream to the cells. As the blood passes through the lungs, oxygen is added to it and carbon dioxide is removed. The heart also pumps blood to the kidneys which filter and remove other waste products of the body. The immune system attacks invaders to keep the body alive and healthy.

What happens if one or more of the systems are not functioning properly? The body gets sick. The problem may be caused by a nutritional deficiency or from a disease. But whatever the reason for the breakdown, the body is impaired. Unfortunately, the breakdown in one system usually affects other systems as well.

In diabetes, the pancreas produces insufficient insulin—a hormone. Insulin is responsible for getting sugar (glucose) from the blood into the cell, where it is burned for energy. Without insulin, the sugar stays in the blood and begins to build up. The excess sugar in the blood can harm the arteries and veins, the eyes and the kidneys. While the original problem was hormonal (not enough insulin), untreated, the problem spreads to the eyes, circulatory system and excretory system, causing damage to these organs and organ systems.

Systems Work Together

The chart below shows how a disease of one organ system affects others.

High blood pressure, discussed in more detail in a later chapter, decreases the ability of the heart to pump blood through veins and arteries. This can cause a decrease in the nutrients delivered to the cells and cause less blood to flow to the kidneys, decreasing their function.

Diseases of the bowel—Crohn’s, inflammatory bowel disease, celiac sprue, etc. —interfere with the intestines’ ability to absorb nutrients. Therefore, fewer nutrients are being taken into the body, and fewer nutrients are available to the cells. Depending upon the severity of the disease, the decrease in nutrients may be small or large.

Providing cells with proper nutrients is critical to their functioning. It prevents system breakdowns that are caused by lack of nutrients. Unfortunately, eating well and having adequate nutrients may not always prevent diseases caused by factors other than diet and nutrition.

Macronutrients

An essential concept in nutrition is macronutrients carbohydrates, proteins and fats. “Macro” means “large”; you need large amounts of them, compared to micronutrients, such as vitamins and minerals, which are required in much smaller amounts.

Macronutrients CARBOHYDRATES, PROTEINS, FATS

  • “Calorie Carriers” are burned for energy
  • Contain vitamins/minerals
  • v Have specific functions in the body
  • Are essential in the diet

We call macronutrients “calorie carriers” because all of the calories in our diet come from these three substances.

These macronutrients are what the cells burn for energy. A “calorie” is the unit of measure for energy. How many calories a person needs to eat in a day is determined by the energy needs of every cell in the body. As you will see later, each macronutrient has functions in the body besides providing energy. Carbohydrates are part of the cell membranes (albeit a minor part), proteins are the building blocks of all cells, fats are the basis of specific regulatory substances. Foods that contain macronutrients also contain vitamins and minerals.

This is an important point: vitamins and minerals do not provide energy. They are necessary in the process that makes energy, but they are not the substance the body “burns”. Many people think “If I take a supplement with B vitamins, I’ll have more energy.” But B vitamins don’t make energy; they are important to help you burn carbohydrates for energy, but there’s no energy in any vitamin or mineral.

We get energy only from macronutrients—carbohydrates, proteins, and fats—and they are found only in food. If you do not have enough vitamins and minerals, they will interfere with energy production. But more vitamins and minerals will not increase energy production. The diagram below shows that food is the source of all nutrients needed by the body.

Where Cell Get Nutrients

Energy Production

The drawing below illustrates how the macronutrients provide energy. The body loves to make energy out of carbohydrates; they are the preferred source of energy. You can see why: the body converts carbohydrates directly into a substance called glucose. You’ve heard of “blood sugar”; blood sugar means glucose. Glucose is easily burned by the cells.

Dietary fat is the body’s second preference as an energy source. The body takes fat, breaks it down into fatty acids, and burns that for energy.

Protein is the third preference. The body would rather use amino acids, the components of protein, as building blocks to make cells but it will convert some amino acids to glucose and then burn the glucose for energy. Neither proteins nor amino acids are burned directly for energy; they must be first converted to glucose.

It’s amazing that the body can completely transform one kind of nutrient into another. This is for survival. If you are starving, your body first exhausts its blood sugar, then begins to use its fat stores. To prevent too much fat loss, the body will begin to break down cells and utilize the proteins in them as energy.

Starving people appear to “waste away”; their muscles are broken down to produce energy for their organs, and their fat stores are depleted. The body will decrease its need for calories by reducing the rate it burns energy. These changes are one reason people can exist on very little food for extended periods of time. We’ve all seen pictures of captives or castaways who existed for weeks without food. Their bodies converted muscle tissue protein into glucose to allow their brain and heart to function.

In World War II, a group of conscientious objectors volunteered to serve as guinea pigs in a study to see what would happen to the body when it didn’t have enough calories and nutrients. They found that the body primarily burns stored fat if it isn’t getting enough carbohydrates, but the brain and the heart still need glucose, so the body breaks down its own muscle tissue to provide glucose.

Remember, the heart is muscle, so a starving body can break down its own heart muscle to get amino acids to convert to glucose for energy. That’s one hazard of very low calorie diets.

When liquid diets first came out about 20 years ago, some people became deficient in carbohydrates. To keep their hearts and brains functioning, their bodies had to break down muscle to convert it to glucose for the heart and brain. There were deaths, both during the weight loss and after they began eating normally again, presumably from the loss of heart muscle (to make energy) and possible loss of minerals.

Of course, starvation isn’t our main health problem. Rather, it’s the opposite. Any excess glucose, fat or protein is stored as fat in the body.

In the next chapters, we’ll look more closely at these macronutrients.

CHAPTER FOUR: PROTEIN

Proteins are the building blocks of the body, a part of every cell. Muscles, organs and chemical regulators of the body are all made up of protein. The functions of protein include:

  • Maintenance: the growth of new tissue and repair of existing tissues.
  • Enzyme production: An enzyme is a catalyst. In the last chapter, we talked about converting galactose to glucose. That takes metabolic action, and enzymes are required for that metabolic action. The enzyme itself does not change in the chemical reaction—the substrate changes, but the enzyme remains the same. Many enzymes require vitamins and minerals to work; for instance, there are magnesium-dependent and copper-dependent enzymes. All enzymes are made up of proteins.
  • Hormone production: These chemical “messengers”, secreted by organs, regulate the body’s activities. Insulin, a hormone that regulates blood sugar, is mostly protein. Proteins are involved in the formation of many other hormones.
  • Immune function: Every cell of the immune system requires protein. People who are protein-malnourished have weak immune systems, are much more susceptible to infection, and take a lot longer to heal.
  • Fluid-electrolyte balance: Proteins help maintain the body’s fluid balance. Fluid is present in three main areas of the body: the space inside the blood vessels, the spaces within the cells (intracellular space) and the spaces between the cells (extracellular space). Proteins are large molecules that attract water. By keeping a certain number of proteins in fluid, the correct amount of water is kept in each space.
  • Acid-Base balance: The pH (acidity) of the body is maintained within a narrow range. Proteins are involved in preventing the body from becoming too acidic (pH drops too low) or too basic (pH rises too high).
  • Transport: Proteins are involved in moving nutrients in the bloodstream from one organ to another. They also move nutrients and substances across membranes. They will pick up a substance on one side of a membrane and deposit it on the other side.
  • Energy: Protein, either from the diet or from reserves, is used for energy when the body lacks sufficient carbohydrate and fat. The muscles are the largest protein reserve in the body.
  • Others: Proteins are involved in blood clotting and making connective tissue (e.g., scar tissues, bones and tendons).

Amino Acids

Proteins are made up of individual units called amino acids. There are 20 different ones that the body needs to make proteins for body functions. Nine of them are called "essential"—the body will not make them, so we have to get them in our diet or we will not be able to make any protein. The body will make the other 11. (You may see references to “22 amino acids.” Nutrition scientists disagree on exactly what should be called an amino acid, and some consider the higher number correct. Most dietitians use the lower figure, however).

One amino acid that the body can make, histidine, often isn’t made in large enough quantities, and is now considered essential. Another four are conditionally essential—there are times when the body just can’t make enough and we might need to have them in our diets.

Amino acids differ from carbohydrates and fats in that they have nitrogen as part of their structure. A protein is made by linking up of many amino acids, usually 100 to 300 per protein molecule. That means that each amino acid many appear in the protein molecule many times.

Unlike complex carbohydrates, which are straight chains of sugar molecules, protein molecules fold around themselves and look like a “tangled knot.”

Digestion and Absorption

Digestion of protein begins in the mouth where the proteins are crushed and chewed and mixed in with saliva. Once in the stomach, hydrochloric acid begins to break down the protein strands while a protein enzyme, pepsin, breaks down the protein molecule into smaller parts called polypeptides—shorter strands of amino acids. These polypeptides are moved into the intestines where more enzymes break the polypeptides into strands two and three amino acids long. These are called di- and tri- peptides.

Finally, there are enzymes on the wall of the intestines that break these di- and tri- peptides into amino acids just before they are absorbed into the body. Protein, like carbohydrate, is broken down from a large molecule into individual units before being absorbed. However, some protein is absorbed in the di- and tri-peptide form.

Once the amino acids are absorbed, the body decides how to use those amino acids. It might say, “OK, we need to repair the skin. This person just got cut and the skin is broken. Let’s make new cells for the skin.” So it might be creating new tissues. Or the body may have to make new cells. Some cells live longer than others. The cells in the digestive tract only live about four days. You need a lot of protein to make those new cells. Or the body might need to burn some protein for energy if there is not enough blood glucose or glycogen available. Or if it has all the energy it needs and doesn’t need to make any protein, it converts excess protein to fatty acids, and stores it as fat.

It’s kind of funny that wrestlers and weight lifters take amino acid supplements. They have this belief about protein: protein builds tissue and they’re trying to build muscle. But excess protein does not go to muscle; it will either be used for energy or stored as fat.

What really makes a weight lifter or wrestler stronger is an overall good diet with enough carbohydrate to enable them to withstand intensive training. Amino acid supplements are not going to build more muscle: weight lifting, exercising, and using the muscle while maintaining a normal diet will build more muscle. The body only needs and can use so much protein.

Protein Needs

How much protein is enough? Simply, eight-tenths of a gram of protein per kilogram of body weight, per day. A kilogram is 2.2 lb. To calculate daily protein requirements, divide body weight in pounds by 2.2 to get weight in kilograms (kg), and multiply that by 0.8.

For example, a woman who weighs 130 lb (59 kg) has a protein requirement of 47.2 gm of protein. (130 ÷ 2.2 X 0.8 = 47.2). A 180 lb man would require 65.4 gm of protein. (180 ÷ 2.2 = 81.8 X 0.8 = 65.4). See example below.

Meeting our protein requirement is really not a problem. Most Americans eat about 85 to 100 gm of protein per day, as shown in the chart below. It’s how we meet the requirement that causes problems.

Protein Requirement

The chart below shows how easy it is to get sufficient protein with a balanced diet of 1500 kcal. For instance, in each serving of bread or starchy vegetable there are 3 gm of protein; vegetables have 2 gm, milk has 8 and meat has 7.

If you’re getting eight servings of bread and starchy vegetables, you’ve already gotten 24 gm of protein. That’s half the requirement for a 130 lb woman. If you’re eating meat, you get 7 gm/oz; a 5 oz serving is 35 gm, almost the whole protein requirement for the woman. Milk has as much protein as meat; two servings gives you 16 gm. If you had all of your servings in these food groups, you would have 85 gm a day.

The idea that we don’t get enough protein a myth. In most cases we get more than enough—and in some cases, too much protein may be harmful. The body has to take nitrogen away from protein to convert the protein to energy or fat. The kidneys get rid of nitrogen by excreting it in the urine. This places a big load on the kidneys. They have to do extra work and use body water to do it, so excess protein can also cause dehydration if the water used to clear the nitrogen is not replaced.

Meeting Protein Requirements

For most people in the United States, adequate dietary protein is not a problem. It’s very uncommon to see a protein deficiency except in extremely low-income families, the elderly, chronically ill people, and people who have trouble preparing food. They might eat foods that are very low in protein, especially if they are eating little meat or dairy products.

“Complete” Protein

There’s one common misconception about protein. Many people assume that if you don’t eat meat or drink milk, you need to be extra conscious of protein to obtain all the essential amino acids. Vegetarians sometimes are concerned about “food combining”—eating specific foods at the same meal to achieve a proper balance of complementary proteins. They needn’t be.

There are, as we said, nine essential amino acids. When the body makes protein, it will only utilize amino acids to the level of the amino acid present in the smallest amount. It will only use that much of all the other amino acids, as shown in the figure below.

Limiting Amino Acids

That’s the whole concept of “complementary proteins”, or complementary amino acids. People say “Eat beans and corn”—the idea is that corn might be low in one amino acid and beans might be low in another, so when you eat the two together, the combination will balance.

By combining two foods, each with a different limiting amino acid, you create a food that no longer has limiting amino acids. This combination has as good a protein value as if you were eating meat or milk, which have all the amino acids in much higher quantities than plant sources.

But plant sources are just as good, and you don’t even have to eat complementary proteins at the same meal. The body has a supply of amino acids that are available for use. It can get the missing or deficient amino acid from this pool, which is supplied by the breakdown and rebuilding of cells.

All you have to do is eat complementary proteins within a day because the body will have a certain amount of free-floating amino acids that it can draw on to get them all up to the level that they need to be. That’s good news for vegetarians—and for those who cook for them. The chart on the next page shows the foods that have complementary proteins.

Complete Protein Combinations

  • Lentils + wheat
  • Legumes + cereals
  • Leafy vegetables + seeds, whole grains
  • Soybeans + rice
  • Peas + wheat
  • Beans + corn, rice
  • Sesame seeds + leafy vegetables, grains

Seventy years ago, Americans’ dietary protein came in equal proportions from vegetable and animal foods. Today, 70 percent comes from animal sources. We’ve seen a shift from reliance on plant sources to reliance on animal sources.

With these animal sources, we get protein but we also get fat. All animal protein sources have little to no fiber. Plant sources of protein have very little fat and are high in fiber. The issue is not whether we get enough protein, but what other nutrients are in the protein foods.

Where you choose to get protein makes a big difference in the overall composition of your diet—and as we’ll see, in your health.

The chart below shows some differences between plant and animal proteins.

Protein Sources

CHAPTER FIVE: FAT

The third macronutrient, and the most complex in terms of implications for diet, is fat. Fat has several roles to play in the body and in our diet.

  • Fat is the chief storage form of energy in the body. As we noted in earlier chapters, excess calories are stored in fat cells.
  • Stored fat cushions your body’s organs. All organs—heart, kidneys, liver—have fat pads around them for protection.
  • Fats are structural. Cell membranes have fat as part of their structure.
  • Fat in our diet helps us absorb some vitamins that can only be carried in fat—vitamins A, D, E and K—the “fat-soluble” vitamins.
  • Dietary fats are also used to produce prostaglandins, other regulatory substances similar to hormones. Prostaglandins are involved in fluid balance, heart activity, blood clotting, inflammation and the immune system. Fats are precursors of prostaglandins—one component of them.
  • Fats are necessary for healthy skin. People with eczema, psoriasis or other skin conditions sometimes need to increase the fat content of their diet or change the types of fats they eat.
  • They add flavor to foods. That’s the biggest problem with cutting down fats: the food doesn’t seem to taste as good. That’s true, it doesn’t—when you’re used to the flavor coming from fats.

Fatty acids

Fatty acids are the individual units of a fat which combine to form a fat or an oil. Fatty acid molecules vary in their number of carbon atoms—usually either 8, 10, 12, 14, 16, 18, 20, or 22 carbons long—and they’re saturated or unsaturated.

One common misconception is that a fat is either all saturated or all unsaturated. People ask, “What’s an unsaturated fat?” I can tell them that corn oil, for example, is 70 percent unsaturated, but there is no fat or oil that is 100 percent saturated or unsaturated.

Fats and oils have more than one fatty acid, and the combination is what determines saturated and unsaturated status. We can classify fatty acids as saturated, monounsaturated or polyunsaturated. These terms refer to the structure of the molecule—specifically, the number and location of the shared electrons (called bonds)that link atoms in the chain-like molecular structure. Chemically, saturated fatty acids have no double bonds (two shared electrons together) in their chains of carbon atoms, monounsaturates have one double bond and polyunsaturates have more than one double bond.

The chemistry isn’t important; what is important is knowing that these types of fatty acids function differently in the body. Characteristics of the three kinds of fats are shown below.

W= Omega

Characteristics of Types of Fats Saturated

  • One double bond
  • Liquid at room temperature
  • No effect on serum cholesterol

Monounsaturated

  • No double bonds
  • Hard at room temperature
  • Raise serum cholesterol

Polyunsaturated

  • More than one double bond
  • Liquid at room temperature
  • W-3 found mostly in fish
  • W-6 found mostly in plants
  • Variable effect on cholesterol and triglycerides

W-3 and W-6 Polyunsaturates

Note that we have one more distinction to make about fats: Polyunsaturates can be classified as omega-3 or omega-6 (usually written W-3 and W-6 and sometimes as n-3 and n-6) polyunsaturated fatty acids. The difference between these polyunsaturated fatty acids has to do with their molecular structure. Omega-3 polyunsaturated fatty acids are found mostly in fish; W-6 polyunsaturated fatty acids are found mostly in plants. Polyunsatured fatty acids are often abbreviated PUFA.

Not only do W-3 and W-6 fatty acids have different molecular structures, they function very differently in the body. Fatty acids are the precursors to prostaglandins, substances that are involved in immunity, blood clotting, inflammation and other body functions. When intake of W-6 is too high, a decrease in immune function and an increase in blood clotting and inflammation may occur. When more W-3 fatty acids are eaten to balance out the W-6 fatty acids, immune function is enhanced and there is less blood clotting and inflammation.

In certain diseases (e.g.,heart disease) it is preferable to decrease blood clotting to reduce the likelihood of the blockage of an artery by a clot which can cause a heart attack. Decreasing inflammation is important in people with inflammatory diseases such as arthritis, lupus and other autoimmune diseases, but also heart disease. Inflammation of blood vessels may increase the risk of a heart attack.

Saturated, monounsaturated and polyunsaturated fatty acids function differently in the body—specifically, they have different effects on blood cholesterol levels. Saturated fats tend to raise blood cholesterol. When we’re trying to reduce someone’s cholesterol levels, we usually start by seeking ways to reduce the saturated fats in their diet. Monounsaturated fats seem to have little effect on serum cholesterol levels, while polyunsaturated fats may lower serum cholesterol. However, since the majority of polyunsaturated vegetable oils contain mostly W-6 fatty acids, their intake should still remain as low as possible. It is important to remember that if a person is eating too much fat, even polyunsaturated fat, serum cholesterol may not be reduced by switching the type of fats eaten.

The chart on the next page shows the composition of some common oils. Each oil is made up of a variety of fatty acids; some are saturated, others monounsat-urated or polyunsaturated (PUFA). The PUFAs are broken down into W-3 and W-6 fatty acids. The vegetable oils are liquid at room temperature. Therefore, they contain more PUFA than lard which is hard at room temperature, and is therefore more saturated.

Types of Fats in Common Oils

A common question is, “What’s the best oil to use?” Let’s look at canola oil; it’s only about 5 percent saturated. That’s good, because saturated fat raises serum cholesterol. It’s also very high in monounsaturated fats, which is good, not that high in polyunsaturated fats and contains about 10 percent W-3 fatty acids. Notice that soybean oil also contains some W-3 fatty acids (about seven percent). Flaxseed has the highest amount of W-3 PUFA of all the oils. Palm kernel and coconut oils, on the other hand, are very high in saturated fat, and will tend to raise serum cholesterol.

We used to say “Avoid animal fats to lower serum cholesterol.” We now add tropical oils to that. The other vegetable oils are somewhere in the middle: safflower, sunflower and corn oil are low in saturates and very high in polyunsaturated fats, while olive oil is very high in monounsaturated fats. Obviously, lard, beef fat, butterfat and chicken fat, all fairly high in saturatedfats, should be avoided. Knowing which oils are high in saturated or unsaturated fats helps you choose more healthful oils.

Triglycerides

Another term you need to know is triglyceride.Triglycerides are the most common fats found in the body. Fatty acids are found in the body as triglycerides, when a glycerol (carbohydrate) molecule combines with or links with three fatty acids, as shown below.

The glycerol makes the triglyceride soluble in blood so it can move through the bloodstream. Fats are not soluble in blood. They will not be transported in the bloodstream unless they have a protein or carbohydrate carrier. Thus, triglycerides are the form in which you find fats in the bloodstream.

Triglyceride

The normal range of triglycerides in the body is about 200 mg/dl of blood. When we talk about a person’s triglyceride level, we’re referring to the amount of fat floating around in his bloodstream. High blood levels of triglycerides can be a problem. These circulating fats can begin to build up on arteries and contribute to atherosclerosis or heart disease.

High serum triglycerides may be caused not only by a high fat diet but also by an excess of calories. Remember, excess carbohydrates or proteins are converted to fat in the liver. When a person has an excess of carbohydrates or proteins, the liver converts them to triglycerides to transport the fat to the cells to be stored. The only way to accurately measure serum triglycerides is to have a person fast for 12 hours. Otherwise, the results may be artificially high due to triglycerides from the recent meal circulating in the blood stream.

Digestion, Absorption and Metabolism of Fats

The digestion of fats is more complicated than that of carbohydrates and proteins. In the mouth, hard fats begin to melt and enzymes begin to break down the large fat molecules. The fats travel to the stomach where dietary triglycerides are broken down to diglycerides and free fatty acids (those not bound to glycerol).

The majority of digestion of fats takes place once they reach the small intestine. Fatty acids can’t be transported in the blood without a carrier. Bile, an emulsifier made by the liver and stored in the gallbladder, is the carrier for fatty acids.

Once fats reach the small intestine, bile is released from the gallbladder and mixed with the fats. This allows enzymes from the pancreas to break down the fats to individual fatty acids. They are mixed with bile and absorbed into the body via tiny particles called micelles.Once a micelle moves across the membrane of the small intestine, the fatty acids and bile are separated. The fatty acids are then converted back into triglycerides to be transported in the blood. The bile is reused to absorb more fat.

The chart below shows what happens to fats inside the body. Dietary fat is converted to fatty acids, which can be stored as fat (in fat cells), converted to energy, converted to glucose (the glycerol portion of the triglyceride) or used to make cell membranes, hormones or prostaglandins.

Metabolism of Fats

Dietary Fat Intake

How much fat do we need? Only 4 to 5 percent of our total calories need to come from fat. They need to come from what are known as “essential fatty acids,” predominantly linoleic acid, one of the W-6 PUFAs.

However, the average daily intake for Americans is 38 percent fat and has been as high as 41 percent. This much excess fat causes problems: obesity, heart disease, cancer, diabetes and arthritis.

Where does all this fat come from? The chart on the next page shows a typical American diet of 15


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