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The Graying of Society: Nutrition, Vitamins and AgingJM
In 1900, 4% of the U.S. population was over the age of 65. Today, that figure stands at 12%. If current projections are correct, the elderly will comprise approximately 20% of the U.S. population by the year 2020. Projections for northern Europe suggest even higher numbers will be present in Europe.
Not only are we growing older as a society, but the lifestyles of the elderly are changing as well. Of all Americans who turned 65 in the year 1990, it is estimated that about half will have spent time in a chronic care institution at some point in their lives. Of that half, approximately 50% will have spent more than a year at the facility. This is an important consideration because the nutritional needs of people living in chronic care institutions differ somewhat from those living independently. One example is the issue of vitamin D. All elderly people are prone to vitamin D depletion, but this is a particular concern for those who are in a nursing home or a hospital, partly because of poor diet and partly because of insufficient exposure to sunlight. These trends have prompted considerable research into the physiology of aging over the past decade. Rob, can you talk about gastrointestinal tract changes that accompany aging and the impact these have on nutrition? Absorption of Fat, Protein and Carbohydrates
RMR
First, I want to talk about how the elderly person handles macronutrients, that is, fat, protein, and carbohydrates. We did a study of nearly 100 people ranging in age from 20 to 95. We put them on a diet of 100 g/day of fat for a period of six days. Because the body's ability to absorb fat was thought to decrease with age, we expected to find that our subjects would excrete more fat but they didn't.(1)
Previous studies, using rats, had shown that the pancreas, an organ that helps the body absorb fat, loses function gradually during the aging process. Although the human pancreas does lose some function with age, this does not prevent the digestion of normal amounts of dietary fat, certainly up to the level of 100 g/day. Our study concluded that the elderly can absorb normal amounts of dietary fat just as well as they did when they were 20. The results would be different if you increased dietary fat to unhealthy levels, say 120-130 g/day. At these very high fat doses, the older person will have absorption problems and start excreting higher amounts of fecal fat than a younger person. Much the same holds true for protein. The older person can handle normal levels of dietary protein just as well as a young person and does not experience absorption problems. However, when eating a very high protein diet, the older person begins to excrete higher amounts of protein. Let me stress that the levels of fat and protein that cause absorption problems in the elderly are far in excess of what an average person would really eat. When it comes to carbohydrates, the situation is less clear because good studies have not been done. One study found increased breath hydrogen, a measure of carbohydrate malabsorption, in elderly people who had been put on an extremely high-carbohydrate diet, (as much as 200g of carbohydrate per meal). In contrast, the younger person's breath hydrogen did not increase.(2) However, the subjects of this study were never screened for certain medical conditions that are common among the elderly that can change the test results. We cannot, therefore, conclude from this evidence alone that older people have any greater difficulty in absorbing carbohydrates than do younger people. Joel, can you address the subject of "sarcopenia" or the wasting away of muscle, in the elderly? We now know this condition is not caused by difficulty in absorbing protein or calories. What is the cause? Sarcopenia: What Can You Do About It?
JM
Sarcopenia is a relatively new term, although the phenomenon has been recognized for many years. As most of us age, we lose lean body mass, primarily skeletal muscle; this seems to occur even if we continue to eat adequately. (Skeletal muscle is the muscle used in basic bodily movements, such as standing, sitting, and walking). We are not sure why this happens. Loss of interest in exercise, as we age, might be a contributing factor but there appear to be other factors as well. Researchers disagree about whether this represents a normal, age-related change or a pathologic one. Regardless of whether you look at it as normal or abnormal, loss of muscle mass, as we age, clearly undermines our ability to carry out tasks of daily living and makes us considerably more susceptible to serious falls.
About five years ago, a number of experiments were done in which injections of growth hormone were used to treat sarcopenia. A group of healthy elderly men who had slightly low growth hormone levels (a common condition in the elderly) received either thrice-weekly growth hormone injections or a placebo over a period of several months. The results showed that the men who received growth hormone increased their overall muscle mass but gained only a small amount of the more important skeletal muscle. Considering these meager results, as well as growth hormone's high cost and side effects, we do not feel that growth hormone, for most people, is the answer for sarcopenia.
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