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Institute of Medicine (US) Committee on Diet and Health; Woteki CE, Thomas PR, editors. Eat for Life: The Food and Nutrition Board's Guide to Reducing Your Risk of Chronic Disease. Washington (DC): National Academies Press (US); 1992.

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Eat for Life: The Food and Nutrition Board's Guide to Reducing Your Risk of Chronic Disease.

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Chapter 5Calories, Energy Balance, And Chronic Diseases

If you eat too much, or exercise too little, you gain weight. If you gain too much weight, you may put yourself at risk for diabetes or a host of other health problems. Those are warnings doctors have been giving us for a number of years now, and the prescription that usually goes along with that message is to eat less and exercise more. That is sound advice.

But in fact, it has been difficult to pinpoint a connection between the number of calories we consume and the risk we might experience for a particular chronic illness. After all, we do not eat just calories. What we eat are carbohydrates, fats, proteins, and alcohol, and the other nutrients, such as vitamins and minerals, that come along with those calories. Thus two groups of people can eat the same number of calories over many years but have very different diets with a different balance of nutrients.

There is also the matter of energy balance—how does the amount of calories you eat compare with the amount of calories your body uses every day? Again, two groups of people might eat the same number of calories with the same balance of nutrients, but one group leads a very active life, whereas the other has a sedentary lifestyle. Over the years, the more active group will gain less weight than the sedentary group, and this might have an effect on the development of chronic degenerative diseases in the two groups. So it is necessary to look at activity levels, energy balance, changes in body weight, and the composition of the diet, in addition to total calories consumed, when searching for a link between calories and chronic illness.

Fueling Up And Burning It Off

On average, American men eat about 2360 to 2640 calories a day, and women eat between 1640 and 1800 calories a day. That is about 10 percent less than in 1970.

The number of calories people eat depends on many factors, including their age, activity level, the weather, if they are on a diet, and, for women, if they are pregnant. Take age, for example. Teenage boys eat the greatest number of calories. But as we age, basal metabolism may decline and activity levels may also decrease. The amount we eat drops, so that by the time we reach retirement age we eat a little more than half as much as when we were teens.

There is a fundamental law of nutrition that goes like this: in order to maintain a constant weight, you have to balance the number of calories you eat with the number of calories you burn. To put it simply,

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If the equation is out of balance, you will either gain or lose weight, depending on which side of the equation is greater. You will not notice any weight change on a day-to-day basis, but you will if the equation remains unbalanced over a period of a week or more. The weight you might gain is stored primarily as fat.

The U.S. population is a good example of what happens when this equation is out of balance. The people in this country may eat 10 percent less than they did in 1970, but, on the whole, the nation has gained weight. The conclusion we can draw from this is that we, as a nation, have become less active over the past two decades. So although we are eating fewer calories than we once were, the rate at which we are burning them has dropped even more. The effect of all this overeating—or underexercising—is that the nation's fat stores have increased.

There are some times when gaining weight and fat is appropriate. Childhood and adolescence are two such times. It is also necessary during pregnancy.

Unless you keep to a regular exercise program as you age, you will find that the amount of fat on your body increases even if your weight does not. If you keep your calorie intake constant, you may have to increase your exercise level as you age to keep a constant weight.

Weight And Chronic Illness

It is not fair to imply that only people who are overweight need to be concerned about their health. In fact, studies of large numbers of people show that it is best—at least from the standpoint of attaining a long life—to be neither too skinny nor too fat. The numbers of deaths and disabilities from heart disease, cancer, diabetes, high blood pressure, gallstones, and osteoporosis all increase in people who are much lighter or heavier than average.

Studying the relationships between body weight and development of chronic diseases is particularly difficult. Some of the relationships are ''confounded" by genetic and other factors—for example, thin people may be heavy cigarette smokers, and the smoking may be the true cause of cancer rather than thinness. People's weight may change in the early stages of a disease, prior to its diagnosis, further complicating the study of the relationship of weight to disease.

It has been known for decades that obesity occurs more frequently in some families than in others. Studies of twins suggest that genetics is an important factor in whether people become obese. Because members of a family share meals as well as other habits, identifying the role genetics plays in the development of obesity and the predisposition to chronic diseases is complex. In addition to obesity, there is increasing evidence that patterns of fat distribution are inherited.

Although there is some concern about the effects of being underweight, most research has concentrated on the health effects of being overweight. This is probably because more people in the United States are overweight than underweight. Whatever the reason, the rest of the discussion in this chapter focuses on the problems associated with being overweight or obese. As defined in the previous chapter (page 70), overweight refers to an excess amount of weight for a person of a given height, and obese indicates an excess amount of body fat compared to muscle and bone. Let's look at each disease separately.

Heart Disease

There is little disagreement that the heavier you are, the greater your risk of having a heart attack. People who are 5 to 15 percent overweight have more than twice the number of deaths from heart attacks as people of average weight. For those who are 25 percent or more overweight, the number of fatal heart attacks is 5 times higher than normal

High Blood Pressure

The evidence is clear: being overweight is associated with having high blood pressure, and losing excess weight usually lowers blood pressure. What is interesting about this, though, is that the effect seems to be related more to body build than to weight itself. People with low waist-to-hip ratios have lower blood pressure than do people with waist-to-hip ratios close to or higher than one.


Excess body fat, which is usually associated with excess body weight, increases the risk of developing noninsulin-dependent diabetes. In fact, the chance of becoming diabetic more than doubles for people who are 20 percent overweight. What is worse, the risk keeps doubling for every additional 20 percent weight gain. For example, if a 5'9" man weight 190 pounds, instead of the optimal 158 pounds, his risk for developing noninsulin-dependent diabetes doubles. If he gains even more weight, up to 227 pounds, his risk is twice as high again.

As in the case with high blood pressure, noninsulin-dependent diabetes is more common in people who carry their excess weight primarily on the abdomen (those with high waist-to-hip ratios). Being overweight in the hips and thighs (resulting in low waist-to-hip ratio), it seems, does not carry as much of a health penalty as far as diabetes is concerned. This seems particularly true for women.

Losing weight is the most effective therapy for people with noninsulin-dependent diabetes. Study after study has shown that decreasing body weight improves the body's ability to metabolize glucose, the biochemical hallmark of this disease.


The evidence shows clearly that being overweight increases the likelihood of developing gallstones. This is particularly true as a person's age increases. For example, by age 60, nearly one-third of obese women can expect to develop gallbladder disease.

The connection between gallbladder disease and weight stems from the fact that being overweight increases the body's production of cholesterol. With the body making cholesterol, the liver excretes more. This raises the level of cholesterol in bile, which leads to gallstones.


The link between cancer and excess weight is not as strong as with the diseases above, but a link does exist. Being overweight increases the risk of endometrial cancer, in particular, although cancers of the gallbladder, bile duct, ovary, breast (in postmenopausal women), cervix, colon, and prostate are also more common in overweight people.

The Dieting Cycle

We are a nation that weights too much, and we seem to know it—a 1985 Gallup poll found that almost 90 percent of U.S. adults believed they weigh too much. As a result, dieting has become a major preoccupation with millions of people in the United States. The same poll found that 31 percent of the women questioned dieted at least once a month, and 16 percent of the women considered themselves perpetual dieters. Other studies have identified even greater numbers of dieters in the U.S. population.

One reason why there are so many people on diets is that most dieters regain the weight they lose. In fact, between 60 and 90 percent of the pounds shed on diets in this country are put back on. To lose these pounds, people go back on diets, and soon a cycle develops—gain, diet, lose, gain, diet, lose, and so on.

The effects of the diet cycle are unclear, but there is some evidence suggesting that it is not a healthy activity. For example, several studies have found that people who gain and lose 10 percent of their weight have a higher risk of developing coronary heart disease than people whose weight remains constant. Repeated cycles of weight gain and weight loss may increase the risk even further. The body may also adjust to the diet cycle by becoming more efficient at using food energy. Thus each attempt to lose weight becomes more difficult. So if you weigh too much now, lose the excess weight by a combination of eating less and exercising much more than you do currently, and if you are not overweight, stay that way.

Copyright © 1992 by the National Academy of Sciences.
Bookshelf ID: NBK235013


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