Dining out in a group a few weeks ago, a friend surprised us by ordering only herbal tea — no food. A scientist, he told us that he’s trying out a new eating plan, based on research demonstrating that restricting calories promotes longevity, and that he had already used up his calorie allotment for the day. He said that he’d first heard of this approach in 2005, when research from Washington University (St. Louis) reported that low-calorie diet regimens significantly reduced cardiovascular disease. The topic has been in the news again, this time based on the results of a long-term study with Rhesus macaque monkeys, who are so closely akin to human beings that it’s thought their results could apply to us as well.
The study randomized 76 adult monkeys into two groups, one eating a normal diet (about 700 calories a day), while the other ate 30% fewer calories in a diet that was balanced to contain all essential nutrients but averaged only about 500 calories a day. (Note: Caloric intake for the study varied from monkey to monkey and was determined individually for each, based on previous eating patterns.) Twenty years into the study, the monkeys who ate less were notably healthier. For example, while 37% of the full-diet monkeys had died of age-related causes, only 13% of the low-calorie group had… there was no diabetes among the low-calorie group, compared with five monkeys with diabetes and 11 with prediabetes in the control group… incidence of cardiovascular disease was reduced by half in the diet-controlled group versus the others. Not only were the restricted-diet monkeys biologically younger than the others (and looked it) — they also had significantly slower rates of brain atrophy in regions that are usually shrunk by age.
I spoke with study author Richard Weindruch, PhD, professor of medicine, University of Wisconsin-Madison, about these startling results. He says that the researchers believe that the diet delays aging and related disease risk factors by shifting the basic characteristics of energy metabolism.
Here is how: Calorie limitation seems to shift the mitochondria, which use calories to create energy in cells, into a different work mode, creating substantial changes in adipose tissue (body fat). Though it used to be thought of as “inert” (using no energy), Dr. Weindruch told me that we now know adipose tissue is “super metabolically active” — and, it turns out, remarkably sensitive to caloric restriction. Though the monkeys ate 30% fewer calories, the diet resulted in a 70% loss in their adipose tissue. This greatly reduced systemic inflammation, which is strongly associated with many diseases, Dr. Weindruch said. This, the researchers believe, is at the core of caloric reduction’s success in antiaging.
Since longevity studies examine maximum life span, the study won’t be complete for another 15 years, when the last monkey would be expected to have died. However, Dr. Weindruch says the research team feels confident about the value of their findings, which now demonstrate a threefold reduction in risk for age-related diseases.
Even more compelling, in my view, is this: Dr. Weindruch told me that until a few years ago, gerontologists had fixated on length of life, but they have now shifted the focus to health span, too. The way these monkeys retained their physical good health, strong skeletons and important areas of brain functioning serves as a clear demonstration of caloric restriction’s efficacy in slowing aging and producing a lengthy health span, he says.
The monkeys were eight to 14 years old at the start of the study and thus considered full-grown adults (average life span is about 26 years, with a maximum life span of 40 years).
Just being thin is not enough to achieve the benefit of caloric restriction. Dr. Weindruch says they have evaluated this carefully in studies and found the metabolic changes responsible for antiaging and longevity require caloric restriction in middle age, with less direct benefit when started earlier in life. He notes that the 30% figure is not magical — if you can manage even a 10% reduction it will contribute to antiaging.
If you’re interested in trying out calorie restriction, start by accurately calculating the number of calories you now consume in order to figure out how many to eliminate. Do this by keeping a daily journal of calories consumed for a sustained period — Dr. Weindruch suggests three months. You can’t use height and weight charts or averages for this purpose, Dr. Weindruch said, because of individual variations in metabolism. He told me that in the research, some monkeys appeared slim but had a high metabolic rate because they were normally big eaters… while others, bulkier ones, naturally ate less. It’s the same with human beings.
If a 30% cutback sounds too draconian, there’s another approach to caloric restriction that may be easier. It’s called “alternate-day calorie restriction.” You eat normally every other day and severely restrict calories (approximately 500 or so) on the others.
Whichever approach you choose, if you do try this make sure you are getting enough nutrients. The good news is, the healthiest foods are nearly always the ones with the fewest calories.
