Want to stay buff well past retirement age? Studies in some very old -- but surprisingly toned -- rats suggest the key to lifelong muscle health is to eat less, and better. With age there is quite a significant loss of muscle function, but dietary caloric restriction basically prevented that loss, so the function of these very old animals is the same as the function of the young animals. Most people view a gradual decline in muscle responsiveness, strength and tone as an inevitable part of aging. And, under typical dietary and exercise conditions, that's probably the case.

With aging, the nuber of muscle fibers decrease, especially type 2 fibers, needed for quick, strength-dependent responses. It's thought that nerve fibers that enervate those type 2 fibers die or recede with age, leading to fiber death and a lowering of muscle tone.

Oxidative stress -- the build-up of "free radicals" that can damage cells -- is a main culprit in this process. Calorie restriction not only reduces the production of free radicals -- the damaging molecules -- but it also seems to have a beneficial effect on antioxidant enzymes that help prevent the damage.

Researchers tested the muscle responsiveness of rats fed either an unrestricted diet, or a diet with 40% fewer daily calories.

As expected, rats free to eat at will had relatively flabby muscles by the time they reached the ripe old age of 26 months -- about the equivalent of a 75- to 80-year-old human.

In contrast, geriatric rats accustomed to the restricted-calorie diet were smaller, leaner, and decidedly buffer. The muscles were quite strong, especially muscles dominated by type 2 fibers. In fact, there was no observed difference in terms of muscle responsiveness and strength between the calorie-restricted, elderly rats and other rats half their age.

Basically you end up with a thinner animal whose muscles function better and the muscle is a greater percentage of the total body weight. That's going to translate to better life function.

Source: Annual Experimental Biology 2002 Conference New Orleans, LA April 23, 2002