One of the keys to a long life is eating less--at least for lab rats and fruit flies. Now, a study of primates, published in this month's American Journal of Physiology, suggests that reducing calorie intake to 30% below the level considered normal could benefit the heart. Rhesus monkeys on this low-calorie diet have higher levels of the "good" cholesterol and lower triglyceride levels, both of which guard against heart disease and stroke in humans. The benefit is greatest for young to middle-age monkeys, and tapers off into old age.
For the last decade, molecular biologist George Roth of the National Institute on Aging has been studying the effects of calorie restriction on rhesus monkeys. All 60 monkeys receive the same diet, but half are allowed only 70% of the calories that a monkey normally consumes. In previous research, Roth and his colleagues found slightly lower blood pressure, better glucose tolerance and insulin sensitivity (meaning the animals are less likely to develop diabetes), and lower body temperatures in the low-cal group. "What we think is that the animals that are restricted are shifting their metabolic strategy from growth and reproduction to a life-maintenance strategy," says Roth.
In the current paper, Roth reports results from monitoring levels of compounds that influence cardiovascular health. Monkeys that ate less had above-normal levels of HDL2B, a type of high-density lipoprotein and a protective cholesterol. The greatest increase (83%) was for the youngest group of monkeys--10 years old--and the least (16%) for elderly monkeys, up to 28 years old. The triglyceride levels of those in middle age, about 13 to 15 years old, were 41% lower than monkeys on the full-calorie meal plan. Juvenile levels were 11% below normal, and the levels were 8% higher than normal for the oldest monkeys.
"It's solid information," says Richard Weindruch, a gerontologist at the University of Wisconsin, Madison. The next step, says endocrinologist William Cefalu of the Bowman-Gray School of Medicine in Winston-Salem, North Carolina, is to connect the findings to disease. Indeed, the monkeys will soon undergo tests to determine whether they are developing heart disease and to what degree, Roth says.