With a low-calorie diet, fat doesn't contribute much to the tumor load. The white numbers indicate the calories consumed per day. Data from David Kritchevsky

New progress against aging

Cut calories, cut cancer, live longer?
Caloric restriction -- the practice of "undernutrition without malnutrition" -- doesn't just slow the progress of cardiovascular disease. It also slows cancer. Calorically restricted rats and mice get fewer and/or smaller tumors than animals that can gobble all they want, says David Kritchevsky, the Caspar Wistar scholar at the Wistar Institute in Philadelphia.

Kritchevsky, who has studied the effects of diet on tumors for more than a decade, says "There's no question, in rats and mice, that any tumor, whether chemically or spontaneously induced, or transplanted, slows or stops growing" under caloric restriction.

Sadly, this isn't a cancer treatment: "The tumor doesn't regress, it just doesn't grow so fast."

Nobody knows why the technique works, Kritchevsky admits, but it could be a matter of simple competition. "Maybe you don't have enough to feed the disease if you barely get enough to feed the host. If you have enough food the tumor gets what it needs, and it eventually wins."

Another clue comes from researchers at Temple University who recently found that removing the adrenal gland neutralizes the protective effect of caloric restriction. This means that an adrenal hormone like cortisol probably plays a role in the cancer-stifling effect.

A good word for fat...
Kritchevsky adds that the fat content of the diet doesn't seem to matter if the calorie count is low enough. Tumor counts in calorically restricted animals eating 25 percent dietary fat were similar to those of free-feeding animals that ate 5 percent fat.

Although caloric restriction may never help prevent or treat cancer, the new recognition that overfeeding may cause tumors has led to changes in the way drug toxicity tests will be done. Since overeating, rather than the chemicals being tested, might be causing tumors in lab animals, in the future, animals will be eating fewer calories .

So no matter what happens to the human diet, the new information could be responsible for hunger pangs in the labs. Laboratory animals, Kritchevsky says, "Get too much food. A lab rat sits around and eats. It's a couch potato. The only thing it doesn't have is a TV."

We're burning up to discuss the role of free radicals in aging.

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