B A Ochia
Food, like sex, is regarded as one of the sources of pleasure that stay with us throughout our lives. The idea of using food to modify or influence human longevity has fascinated the public for a long time. The mass media has capitalised on this with great interest by featuring controversial topics in nutrition. Such titles as “Vitamin C: The Dosage Debate Goes On; Importance of Vitamins for the Elderly; Fat in Food May Not Count; and Eating to Live Longer” are but a few examples of headline items.
In many developed countries proposals have been made from time to time for nutritional intervention in order to delay, postpone or even prevent the physical signs of ageing and, presumably, to extend the life span of the individual through adequate nutrition. However, scanty attention is given to promoting a complete knowledge of the nutritional needs of humans, especially those individuals entering late middle age and early old age. Most of our knowledge of the nutritional needs of humans has been derived from studies on younger persons and laboratory animals, especially rats and mice.
DIETARY ENERGY RESTRICTION
There are limitations in extrapolating results from rats to humans. However, the animal studies have yielded valuable information regarding human nutrition and ageing. One obvious example of this can be seen from classical experiments started by one Professor H S Osgood and completed by one of his pupils, Clive McKay. Osgood had the notion that people in America ate too much. He used himself as a guinea-pig and tried to induce satisfying satiety restricted food. To accomplish this he filled out his diet with washed sand and/or tiny glass balls. This sort of restricted feeding had little or no effect on life span, as Osgood diet at a normal age.
McKay continued to test Osgood’s hypothesis. He divided young rats into two groups, the one fed on a diet containing all the necessary nutrients but deficient in energy, and the other on a normal diet. The rats on the normal diet grew up, aged and diet at the age normal for rats. On the other hand, the energy-deprived rats remained young and sexually immature for a longer period and finally went through their normal life cycle and died at an age twice that of the energy-sufficient rats. Subsequent researchers discovered that not only did the energy-deprived rats mature later, they but also had lower concentrations in their blood of cholesterol, triacyglycerides and phospholipids.
Studies on mice gave similar results as did those on rats. However, the mice studies further showed that development was not necessarily delayed when using the energy-restricted diet. Both life span and reproductive life of mice were nearly doubled by feeding them for 2 out of every 5 days. Restricted feeding seemed to postpone the appearance of all aspects of ageing changes, even including the emergence of tumours. The use of low-energy diets for delaying ageing depends mainly on timing. Animal studies have indicated that food restriction very early in life may contribute to malnutrition and consequent premature ageing.
It might be asked, since animal studies have shown such remarkable results, why have scientists not used human subjects to repeat the animal trials? One answer to the question may indirectly come from the observations made in isolated human populations during the Second World War, which showed that under nutrition, resulting from, and combined with, appalling living conditions, produced young individuals who showed signs of premature ageing. Another, inherent in gerontology, is that human ageing is measured only by observing how long people live. The way to see if diet influences ageing is to run an experiment on human subjects from their infancy until they die, a period which could span 80 years, or more. This is an awfully long time to wait for the results of an experiment. Yet a third answer is that we human beings like good quality of life. Who will willingly permit himself or herself to be subjected throughout life to a test-type dietary regimen, compounded by the attendant measurements and restrictions demanded by the researchers? Therefore, we have to rely on results from experimental animals for a long time to come.
NUTRITIONAL NEED OF THE ELDERLY
In many countries increasing attention is being paid to the problems of ageing because of the increase in the total number and proportion of people living beyond the age of retirement. Various factors have contributed to this; among them are the improvements in medical facilities, advances in environmental hygiene and better nutrition. This extension of life span has also exposed various complications associated with ageing, reminding one of the warning given by Plato, “Beware of old age, for it does not come alone”.
Research into the nutrition of he elderly is complicated by the sheer diversity among the elderly in terms of genetic differences complicated by varying degrees of emotional and physical traumas, stresses and poor nutritional states that they had undergone through from childhood to adolescence and full maturity. There are wide variations among the elderly in their ability to eat food, digest it and absorb the nutrients. Despite these problems, scientists have been able to study the ways in which nutrition can affect the ageing process and also how the physiological changes associated with ageing influence the requirements and utilization of dietary nutrients.
Various factors affect nutrient intake of the elderly. Among these are the loss of teeth and the weakening support of the jaw bone due, probably, to dietary vitamin D deficiency and low calcium: phosphorus ratio, resulting in chewing difficulties. The next is neuromuscular in-coordination that makes handling of cutleries embarrassingly difficult and forces the elderly to make considerable dietary changes which more often than not result in reduced nutritional value of the diet. Other factors are physiological and involve diminished sense of taste and smell due, probably, to zinc deficiency, and loss of appetite due to loneliness, anxiety and unhappiness. In addition, feeding habits cultivated in childhood and adolescence, affect food choice in middle and old age. These food preferences are difficult to break, especially if they are associated with pleasant memories. Economic constraints that dictate the type of food products some elderly subjects purchase influence their nutrient intake. For the well-to-do there is no problem; but for the less well-off the tendency is to budget in favour of low-cost foods which will satisfy their hunger and energy needs. In other words, they purchase cereal-based products instead of the more expensive items, such as, meat, fruit and fresh vegetables which are better sources of protein, vitamins and minerals.
There are standards set for nutrient needs of the elderly. According to the Expert Consultation of Food and Agriculture Organization/World Health Organization/United Nations University 1985, healthy elderly people have a mean daily protein requirement if 0.6 to 0.75g/kg body weight, values equal to, or more than those for young adults. Tabulated values are available for all the other nutrients.
NUTRITION AND COURSE OF DISEASES
How does diet influence the course of diseases that afflict old age? These diseases include cardiovascular disorders, atherosclerosis, osteoporosis, diabetes, obesity and cancer. Since it is well known that diet can influence the course of these diseases, the effect of nutrition on natural ageing becomes apparent. A selection of these diseases will now be discussed.
As age increases, ability to utilise glucose is gradually impaired. Reports from national public health surveys have confirmed that death rate from diabetes mellitus progressively increases with age. Population studies suggest that diet or specific dietary nutrients can be of critical importance in the frequency of occurrence of diabetes. For example, studies on laboratory animals indicated that caproic acid and some of the amino acids derived from it, such as, norleucine, leucine, methionine, glutamine and norvaline when added to the diet, favourably influenced their blood glucose concentration.
Obesity is associated with, and complicates the course of, diabetes and other degenerative ageing-associated diseases. The rate of body fat accumulation is generally associated with the level of energy expenditure and retention. Tests on chickens have shown that manipulation of dietary composition, especially the proportion of protein to other nutrients can be used to control body fat content. In mammals the situation is not as simple, and in humans small changes in food intake have not produced the expected clear-cut alterations in body weight and fat content. It is believed that the percentage of fat and of fatty acids in the diet is crucially important in the development of obesity.
Substantial evidence exists to suggest that human diets high in butter fat and coconut oil, and whole egg tend to increase blood cholesterol, and that populations with blood cholesterol values have high incidence of coronary diseases. The relation between diet and hypertension is still not quite clearly defined. High intake of table salt has been associated with high blood pressure. Increased potassium intake seems to affect blood pressure favourably. Some studies have indicated that people in soft water areas have a higher death rate from cardiovascular diseases, compared to the general population. But there is no unanimity on this. However, it is safer to assume that the trace element content of the water may, to a certain extent, affect the health records of those drinking it.
There is a growing body of knowledge to suggest that gastrointestinal cancer is related to diet. Examples are neoplastic diseases of the colon and their relation to crude fibre content of the diet. Nitrosamine associated with bacon, preserved meat and other products are potential carcinogens. Similarly, some polyunsaturated fatty acids, especially when heated, can cause various types of cancer. Residues of pesticides, and some chemicals added to food during processing, as well as anti-nutritional substances inherent in the food are possible carcinogens.
How does society help to improve the nutritional state of the elderly? Concern about the low nutritional state among the elderly, brought about by social, economic or emotional conditions, has resulted in responsible community and private groups providing residential houses, meals-on-wheels and food delivery services for them. For the elderly who live at home alone, regular visits by staffs, home assistants and relatives are commendable. It is known that people with low appetite, caused by loneliness or depression, do enjoy eating out in the company of relatives and friends. Companionship and caring go a long way to improving the dietary intake as well as the quality of life of the elderly.