The American Federation for Aging Research

Can Cutting Calories Increase Longevity?

How does caloric restriction slow down aging?

Overview
Metabolic effects
Hormonal effects
Protection against temperature effects
Down sides

Overview

Caloric restriction acts to slow down some of the destructive processes that take place in cells and tissues with aging¹. Particularly, caloric restriction reduces oxidative and glycation damage, thought to be leading causes of cell aging and death.

Oxidative damage results when free radicals, the toxic waste products of cell energy production, break down DNA, cell walls, and mitochondria, the energy factories of cells. Caloric restriction has been observed to retard and even reverse oxidative damage in aging animals.²

Glycation is the addition or insertion of sugar molecules that takes place in a variety of physiological reactions. Glycation causes damage to proteins and DNA and is thought to be a major cause of degeneration associated with diabetes and other diseases. Caloric restriction also reduces glycation damage in tissues.

On a larger scale, caloric restriction slows the effects of aging on the nervous system, the reproductive organs and the production of hormones in some animals. It has been shown to boost the immune system and delay the onset of certain age-related cancers³.

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Metabolic effects

Probably the most significant effects of caloric restriction in animals occur in glucose and insulin regulation⁴. Glucose is a simple sugar that is one of the major sources of energy for mammals. It enters the circulation after food is digested and circulates until the hormone insulin assists its movement into cells to be turned into fuel or into the liver, to be stored for future use. With age and obesity, mammals such as mice, monkeys and humans develop insulin resistance, which is a drop-off in the ability of insulin to push glucose into cells. With insulin resistance, blood glucose (blood sugar) levels rise, blood insulin levels rise, and cells and tissues are damaged. Diabetes, high blood pressure, hardening of the arteries, heart disease and stroke are some of the consequences of insulin resistance⁵ in humans.

Caloric restriction protects against insulin resistance. An animal whose total calorie (and thus energy) intake is limited becomes much less dependent on insulin for driving the glucose it gets into its cells. This has been observed in numerous species of laboratory mice and rats; recent studies in non-human primates have also demonstrated caloric restriction's beneficial effects on reducing insulin resistance^6,7.

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Hormonal effects

Caloric restriction has been shown to increase the ability of aging rodents to respond to physical stress through increased production of glucocorticoids, the stress hormones. As mammals age, the neurotransmission of signals between the brain and the adrenal gland is altered and the release of these stress hormones falters. Caloric restriction improves this stress response⁸.

Another hormone that may accelerate aging is growth hormone. Caloric restriction can correct imbalances in circulating growth hormone levels, which may be another reason for the benefits of caloric restriction in aging animals⁹.

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Protection against temperature effects

Another interesting cellular change noted in aging rodents subjected to caloric restriction is their ability to resist the damaging effects of hyperthermia, or elevated body temperature. Older mammals are far more likely to suffer adverse effects from hyperthermia than are younger ones. One reason for this is the reduced ability of older mammals to produce protective substances called heat shock proteins. Caloric restriction enhances the ability to make heat shock proteins¹⁰.

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Down sides

Caloric restriction leads to reduced ability to deal with hypothermia (lowered body temperature) ¾possibly associated with the individual's lower body fat content. Another problem is that wounds don't heal as quickly in calorie restricted animals as in normal fed laboratory animals.

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