What have researchers discovered about how the manipulation of diet affects the longevity of animals? What implications does this information have for humans?

Question

What will be an ideal response?

Answer 1

Decades of research has revealed that animals live longer and have fewer age-related diseases when their energy intakes are restricted. These life-prolonging benefits become evident when the diet provides enough food to prevent malnutrition and an energy intake of about 70 percent of normal; benefits decline as the age of starting the energy restriction is delayed. Exactly how energy restriction prolongs life remains unexplained, although gene activity appears to play a key role. The genetic activity of old mice differs from that of young mice, with some genes becoming more active with age and others less active. With an energy-restricted diet, many of the genetic activities of older mice revert to those of younger mice. These “slow-aging” genetic changes are apparent in as little as 1 month on an energy-restricted, but still nutritionally adequate, diet.
The consequences of energy restriction in animals include a delay in the onset, or prevention, of chronic diseases such as cancer and atherosclerosis and age-related conditions such as neuron degeneration; prolonged growth and development; and improved blood glucose, insulin sensitivity, and blood lipids. In addition, energy metabolism slows and body temperature drops—indications of a reduced rate of oxygen consumption. Restricting energy intake in animals not only produces fewer free radicals, but also increases antioxidant activity and enhances DNA repair. Reducing oxidative stress may at least partially explain how restricting energy intake lengthens life expectancy.
Interestingly, longevity appears to depend on restricting energy intake and not on energy balance or body composition. Genetically obese rats live longer when given a restricted diet even though their body fat is similar to that of other rats allowed to eat freely.
Research on a variety of species—including mice, rats, monkeys, spiders, and fish—confirms the relationship between energy restriction and longevity. Applying the results of animal studies to human beings is problematic, however, and conducting studies on human beings raises numerous questions—beginning with how to define energy restriction. Does it mean eating less or just weighing less? Is it less than you want or less than the average? Does eating less have to result in weight loss? Does it matter whether weight loss results from more exercise or from less food? Or whether weight loss is intentional or unintentional?
Extreme starvation to extend life, like any extreme, is rarely, if ever, worth the price. Hunger is persistent when energy is restricted by 30 percent. Furthermore, using animal data to extrapolate to humans, researchers estimate that it would take 30 years of such energy-restricted dieting to increase life expectancy by less than 3 years.
Moderation, on the other hand, may be valuable. Many of the physiological responses to energy restriction seen in animals also occur in people whose intakes are moderately restricted. When people cut back on their usual energy intake by 10 to 20 percent, body weight, body fat, inflammatory proteins, growth factors, and blood pressure drop, and blood lipids and insulin response improve— favorable changes for preventing chronic diseases such as some cancers, type 2 diabetes, hypertension, and heart disease. Some research suggests that fasting on alternative days may provide similar benefits.