Some researchers are investigating the relationship between these genes and hormones and the one other treatment that has been shown to extend lifespan: a semistarvation diet. Since insulin affects an organism's use of food, such a connection would not be surprising. In the 1930s, Clive M. McCay, a Cornell University scientist, fed rats diets high in nutrients but very low in calories, a treatment later found to lower insulin levels sharply. He found that the half-starved rodents lived 20 to 40 percent longer than rats given a normal diet. Later scientists found similar effects in creatures ranging from yeast and fruit flies to fish.
A few individuals have also tried to extend their lives by eating carefully balanced, low-calorie diets. Science has not proved whether this approach really works, however, and most people probably would not want to adopt it even if it did. Some scientists think that eventually a drug or gene therapy will provide the benefits of a low-calorie diet without its unpleasantness. Alternatively, some nutritionists think that lowering the amount of carbohydrates in the diet will work as well as reducing calories. Carbohydrates, especially those in sugar and foods that are easily converted into sugar, such as candy, potatoes, pasta, and rice, raise the amount of insulin in the blood and affect the way cells react to this hormone. (Other carbohydrates, such as those in beans and whole grains, produce a much smaller increase in insulin.) Low-carbohydrate diets are popular today, and some nutritionists believe that such diets, even when they are not low in calories, can make people healthier as well as helping them lose weight. Cynthia Kenyon herself eats a diet low in easily converted carbohydrates.
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