George Burns once said: "The trick is to live to 100. Very few people die after that." Although most people will not attain that goal, as a nation we edge closer every year. Today, a person who reaches 65 can reasonably expect 15 more years of life. The population over 65 is the most rapidly expanding group in our country. By the year 2000, 30 percent of Americans will be 65 or older.

Older people have some very special nutritional needs, many centering on the maintenance of good health, the prevention of chronic debilitating disease and the enjoyment of the best quality of life possible. Nutrition plays a major role in satisfying all of these needs.

To maintain good health, any person must consume a good diet. For someone 65 or older, this is particularly important. But is a diet that is good for the average 30-year-old also good for a person in the seventh or eighth decade? :: :: ::

Strange as it might seem, this question has been asked only recently, and the answer is far from being known. Studies have shown that older people require fewer calories than they did when they were younger. A change occurs in the composition of the body, presumably as a part of the aging process: There's a relative increase in the amount of fat being deposited and, at the same time, a loss of muscle mass. Thus, even the "thin" older individual is "fatter" than the thin younger individual; at any given weight, the average person over 65 is carrying around more fat than his or her younger counterpart.

To minimize this deposition of fat, fewer calories should be consumed. In addition, most older people are less active than in their younger years and should consume fewer calories.

Finally, a subtle change seems to occur during the aging process that results in a more efficient handling of calories, thus requiring fewer calories to maintain the machinery of the body. The reason for this change in caloric efficiency is not known.

Among the essential nutrients required in smaller amounts by older people are:

Protein. Part of the aging process involves an impairment of the kidney's ability to excrete waste products, particularly the waste products of protein breakdown.

A second reason for reducing the amount of dietary protein is to protect your bones. The higher the protein intake, the more calcium is lost from bone. Older people in general and older women in particular are very susceptible to osteoporosis and the fractures that accompany this serious and debilitating condition. A lower-protein diet may reduce the rate of bone loss and thereby offer some protection. So older people should consume adequate amounts of protein (since protein is essential) but not too much. Because the typical American diet is very high in protein, older people must be careful.

The most practical way to reduce protein intake is to emphasize carbohydrates: fruits, vegetables, grains (rice, wheat, corn, rye and barley) and other foods derived from plant sources. At the same time, you will be reducing the higher-protein foods derived from animal sources.

Fat. Knowing how to limit the amount of fat in the diet is important for everyone, but doing so is necessary for older people for somewhat different reasons.

Whereas younger people should reduce their fat intake primarily to prevent atherosclerosis, coronary artery disease and perhaps certain cancers, older people must consider more than just these diseases. Having lived beyond 65, they have passed the peak incidence of coronary artery disease. On the other hand, they require fewer calories, and it is difficult to reduce calories without focusing on fat, since each gram of fat contains twice the number of calories as a gram of protein or carbohydrate. Limiting intake of "fatty meats" and using low-fat dairy products is the best way to reduce fat intake.

Iron. Older people require less of other nutrients as well. For example, with the onset of menopause a woman's iron requirement drops, and even though iron may not be absorbed as well by older people, in women the cessation of repeated blood loss more than compensates for this. By contrast, in men the requirement for iron will increase as a consequence of the reduced rate of absorption.

To be absorbed most efficiently, iron must be chemically changed by the hydrochloric acid in the stomach. Older people have relatively less of this acid because many of the cells lining the stomach that secrete the acid have been lost. In addition, the cells of the stomach secrete a substance called intrinsic factor, which is needed for vitamin B12 to be absorbed. As with hydrochloric acid, secretion of intrinsic factor by older people is often reduced and therefore their vitamin B12 requirement is increased.

Calcium. Another important mineral is calcium. To minimize the amount of bone loss that occurs during the later years, particularly in women, people should eat foods that contain adequate amounts of calcium. Although there is no evidence that older people require more calcium, they often don't get enough because they require fewer calories and may not eat many dairy foods. This reduced calcium intake may aggravate the process of bone loss.

Fiber. Perhaps the most important potential nutrient deficiency seen among older people is a deficiency in dietary fiber. Constipation is an extremely common and often debilitating problem for older people. This problem can frequently be alleviated by increasing the amount of fiber in the diet.

Fiber is simply complex carbohydrate that is not digested by the body. The pectins in vegetables and the cellulose and hemicellulose in fruits, vegetables and bran are all forms of fiber. Fiber traps water and softens the contents passing through the large intestines, thus relieving constipation and lessening the risk of a more serious problem in the elderly, diverticulosis.

A diverticula is an outpushing of the wall of the large intestine -- something like a small balloon. It is caused by internal pressure on a weakened area of the intestine. The higher the internal pressure, the greater the risk for diverticuli to form.

Fiber softens the contents passing through and thereby reduces the need for high pressure within the bowel. The result is that these diverticuli are less likely to form. Since diverticuli may become infected, leading to a disease called diverticulitis, a diet containing adequate fiber is extremely important in protecting against this potentially serious disease. :: :: ::

Finally, I must mention a problem very common among the elderly, the problem of drug-nutrient interaction. As people get older, they are much more likely to be taking medications, often on a regular basis. More than half of all the drugs consumed in the United States are purchased by people over 65. Many drugs will interfere with the absorption or utilization of certain nutrients. Antacids can reduce iron absorption; aspirin can cause iron loss; dilantin increases the requirement for folic acid; high-fiber laxatives may reduce the absorption of certain minerals. The list is very long. If you must take medications, check with your doctor regarding any dietary modifications you should make.

So what kind of a diet should an older person consume? A diet that is about 10 percent lower than before in calories and emphasizes complex carbohydrates (pasta, rice, whole grain cereals and other starchy vegetables). Such a diet will normally contain an adequate amount of fiber. At the same time, it is important to consume protein of high quality in moderate amounts and in a form that is accompanied by minimal amounts of fat. Fish, fowl and low-fat dairy products are best for this purpose. The dairy products will be rich in calcium as well. For iron, the dark meat of chicken or turkey is better than the white meat. Such a diet will be adequate in vitamin B12. It is close to what has been recommended for all Americans, so the older person need not make radical dietary alterations. If you have been eating right all your life, just continue; if you haven't, it's never too late to change.

Do you need to take dietary supplements? Probably not, if you eat the kind of diet recommended above. But many older Americans do not. In that case, a multivitamin-mineral preparation may offer some protection, but remember: It's no substitute for a good diet.

Myron Winick, MD, is the Williams Professor of Nutrition at the College of Physicians and Surgeons, Columbia University, New York.