Two new studies from the Institute on Aging shed more light on the effects of a calorie-restricted diet, an issue that has received increasing attention.
A handful of studies have shown that eating fewer calories can -- over the long haul -- lower your risk of cancer and kidney disease and protect brain cells from Alzheimer's and Parkinson's diseases as well as stroke, says Mark P. Mattson, PhD, chief of the neurosciences lab at the National Institute on Aging.
His study appears in the latest issue of the journal Proceedings of the National Academy of Sciences.
In it, he explores this concept more deeply: Is eating fewer calories the important factor, or is intermittent fasting -- skipping meals -- the key? The study shows that -- in mice, at least -- skipping meals improves glucose metabolism and insulin levels, and it also seems to protect brain cells.
"We think that intermittent fasting puts a mild stress on the body, so cells respond by enhancing their ability to cope with more severe stress and resist disease," Mattson tells WebMD.
In his study, one group of mice fasted every other day but was allowed to eat unlimited food on the intervening days, thereby making up for missed calories. A control group of mice fed freely. A third group was fed 30% fewer calories every day than the control group received.
To test the diets' effects on brain cells, mice were given a neurotoxin called kainite, which damages nerve cells in a brain region called the hippocampus -- an area critical for learning and memory. In humans, nerve cells in the hippocampus are destroyed by Alzheimer's disease.
The meal-skipping mice had nerve cells that were more resistant to neurotoxin injury or death -- more so than the other mice.
Another of his studies, published recently in the FASEB Journal (Federation of American Societies for Experimental Biology), compares groups of rats on similar diet plans. It shows that fasting rats have "clear decreases in blood pressure and heart rate as great or greater as can be achieved with aerobic exercise."
But is skipping meals healthy for people?
"We don't recommend people go whole days without eating," Mattson tells WebMD. "However, we think this does suggest that skipping meals may not be bad -- in fact, it may be good for you. In terms of our evolution, it's only very recently that humans began eating three meals a day plus snacks. Our ancestors had to compete for limited supplies of food, had to go many hours, days without food."
It's a big leap, comparing mice to people, he tells WebMD. "It's possible that intermittent fasting could help some people in terms of aging effects," he says. However, the relevance of this study to humans is "very limited."
People would stand a better chance of improving their health -- and reduce risk of diabetes and other diseases -- if they ate a healthier diet, got some exercise, and lost some weight, Greenberg says.
"Lots of people try intermittent fasting -- they call it dieting," he says. "Unfortunately, the vast majority of people on diets regain their weight. It's been studied over and over again and shown to be true. It fact, there's evidence that skipping meals may actually impedeweight loss."