Lifestyle Choices

The number of calories needed per day depends upon the body’s metabolic rate (MR), which, in turn, depends upon such factors as age, sex, size, muscle mass, glandular function, emotional state, climate, and exercise.

Your basal metabolic rate (BMR) is the basis for your caloric needs. The higher the BMR, the more calories you burn at rest. Your MR is a combination of your BMR and calories expended in normal daily activities. The MR is usually higher in males, young people, large people, lean and muscular people, and in nervous people; in cold and hot weather; and during exercise.

A moderately active college-age woman needs about 2,000 calories per day, while a moderately active man of the same age needs about 2,800 calories. A female athlete in training might burn 2,600 to 4,500 calories; a male athlete in training may expend 3,500 to 6,000. If weight remains at the optimum, the caloric content of the diet is correct. If weight varies from optimal, the caloric content of the diet may need to be altered.

Excess fat in the diet, particularly saturated fat, is associated with the increased risk of disease and is inversely related to optimal health.

Humans need some fat in their diet because fats are carriers of vitamins A, D, E, and K. They are a source of essential linoleic acid, make food taste better, and provide a concentrated form of calories, which serve as an important source of energy during moderate to vigorous exercise. Fats have twice the calories per gram as carbohydrates.

There is evidence that total fat in the diet is associated with atherosclerotic cardiovascular disease; breast, prostate, and colon cancer; as well as obesity. Saturated fats come primarily from animal sources such as red meat, dairy products, and eggs but are also found in some vegetable sources such as coconut and palm oils. They are considered most likely to contribute to the health problems mentioned above. In addition, excess saturated fat in the diet contributes to increased cholesterol, and increased LDL cholesterol in the blood.

Unsaturated fats, also a part of a normal diet, are of two basic types: polyunsaturated and monounsaturated. Polyunsaturated fats are derived principally from vegetable sources such as safflower, cottonseed, soybean, sunflower, and corn oils (Omega-6 fats) and cold water fish sources such as salmon and mackerel (Omega-3 fats). Monounsaturated fats are derived primarily from vegetable sources including olive, peanut, and canola oil.

Unsaturated fats are generally considered to be less likely to contribute to cardiovascular disease, cancer, and obesity than saturated fats. When polyunsaturated fats (Omega-6) are substituted for saturated fats, there is a reduction in cholesterol and LDL cholesterol in the blood, but there may be a decrease in HDL cholesterol as well. However, when monounsaturated fats are substituted ,’or saturated fats, cholesterol and LDL cholesterol are thought to decrease without an accompanying decrease in the desirable HDL.

There is very limited evidence that Omega-3 unsaturated fats may inhibit cancers while Omega-6 fats may not have the same effect. Since no group of humans have lived on a primarily Omega-3 polyunsaturated diet for an extended period, this finding has not been verified over time. Omega-3 polyunsaturated oils (fish oils) have been shown to reduce triglycerides, but there is no conclusive evidence that they are especially successful in reducing blood cholesterol.

Humans produce their own cholesterol even when dietary cholesterol is limited. Still, there is evidence that high dietary cholesterol can increase the risk of atherosclerosis and coronary heart disease. Principal sources of dietary cholesterol are organ meats, some shellfish, and egg yolks.

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