CALORIE RESTRICTION AND AGING
A reduced energy intake (‘calorie restriction’) is known to slow down the rate of aging and onset of age-related disorders, such as cancer (breast, lymphomas, prostate), nephropathy, cataract, diabetes, hypertension, hyperlipidemia and autoimmune diseases. This has been demonstrated in a variety of species including chickens and rodents and is also believed to be true for humans. The effects of calorie restriction were demonstrated in the 1930s using laboratory rats. Rats were divided into two groups. One group was allowed to feed freely while the other was fed on a diet containing 30% of the calories of the first group, although they were provided with sufficient protein, fats, vitamins and minerals to maintain normal health. The calorie-restricted rats lived for four years compared with three years for those allowed to feed freely. In addition, the calorie-restricted rats developed fewer age-related diseases.
Studies on calorie restriction have been performed in primates with encouraging results. Long-term studies on rhesus monkeys showed that calorie restriction reduced the incidence of heart disease, diabetes and hypertension and was associated with a decreased concentration of blood cholesterol. Calorie restriction may, however, be difficult to apply to humans because many people may be unable to reduce their calorie intakes by an appreciable amount for the extended period of time required. However, it may be possible to motivate people to do this, especially those with family histories of age-related diseases such as cancer and neurodegenerative disorders.
The mechanism by which calorie restriction increases the life span is unclear but studies have shown that it is associated with a reduction in age-associated mutations when compared with normal diets. This was demonstrated by examining mutations in lymphocytes at four weeks, six months and one year of age.
A high calorie diet may increase free radical-mediated damage as the increased availability of nutrients to mitochondria increases the production of the superoxide radical. Thus, a calorie-restricted diet appears to reduce free radical damage to lipids, protein and DNA and improves the antioxidant status. Calorie restriction in animals has also been shown to reduce levels of tissue AGEs. The benefits of calorie restriction, however, depend on preventing malnutrition and reducing overall calorie intake rather than a particular nutrient.