Low-cal diet may reduce cancer in monkeys

Here’s a fact that people stuffed with Thanksgiving stuffing might well contemplate: According to studies of short-lived species such as worms, flies, and mice, slashing normal calorie consumption by one-third can extend an animal’s natural life span and reduce its odds of diseases such as cancer. Researchers monitoring monkeys on calorie-restricted diets have also seen signs that this strategy can benefit long-lived primates (SN: 3/15/97, p. 162: https://www.sciencenews.org/pages/sn_arc97/3_15_97/bob1.htm) and, presumably, people.

At a gerontology meeting in Washington, D.C., this week, Angela Black of the National Institute on Aging (NIA) in Bethesda, Md., reported for the first time preliminary data suggesting that calorie-restricted monkeys are developing fewer chronic diseases, particularly cancer and endometriosis, than are monkeys that eat as much as they want.

“It’s becoming evident that calorie restriction is having the expected benefits in primates,” says Mark Lane, who heads the NIA primate study.

Started more than a decade ago with both young and middle-age animals, the study has followed 60 female and 60 male rhesus monkeys. Researchers divided them into a group that ate without limit and another that consumed only 70 percent as many calories as the first did.

For each group, Black and her colleagues recently tallied the incidence so far of conditions such as ulcers, cataracts, cancer, endometriosis, and heart disease. Of the 60 well-fed monkeys, 25 have experienced one or more of the chronic diseases, in contrast to just 13 animals from the calorie-restricted group.

The greatest disparity appears in diseases of cell proliferation, such as cancer and endometriosis. The NIA team has found cancer in seven of the well-fed monkeys and in two of the dieting ones. Only one calorie-restricted female has developed endometriosis, while six of the other females have.

In a similar NIA study of 48 male squirrel monkeys, which have a shorter life span than rhesus monkeys, 7 cancer cases have shown up in the well-fed animals over 13 years and none have appeared in the dieting group.

The researchers are now conducting mathematical analyses to determine how likely it is that these disparities result from chance alone, but other scientists find the preliminary results provocative.

“The NIA numbers are very intriguing,” says Joseph W. Kemnitz of the University of Wisconsin-Madison, who also studies a colony of calorie-restricted monkeys. Those animals tend to be younger than the ones in the NIA study, and Kemnitz tells Science News that his group hasn’t yet documented cases of cancer or endometriosis in its monkeys.

It’s not clear how calorie restriction would reduce the risk of endometriosis and cancer, although there’s evidence that it slows cell division, notes Black.

There are also hints from the NIA study and a similar one at the University of Maryland School of Medicine in Baltimore that the monkeys on the low-cal diet are surviving longer, on average, than well-fed monkeys.

Accepting that it’s unlikely that many people can maintain a diet of 30 percent fewer calories than they’re used to, scientists are considering whether drugs can mimic calorie restriction. NIA’s Lane studies 2-deoxyglucose, a synthetic molecule similar to the sugar glucose. Cells take up 2-deoxyglucose as if it were glucose but can’t metabolize it to obtain energy as they do with glucose.

In rodent studies, administering 2-deoxyglucose produces some of the same responses as calorie restriction, such as reducing body temperature and lowering the amount of insulin in the blood. The NIA biologists are now testing whether 2-deoxyglucose treatments extend rodents’ life spans. The drug has significant drawbacks, however. At high doses, it’s toxic throughout the body and can kill brain cells, notes Lane.