Fasting May Be Good for You

It has long been thought that a calorie-restricted diet can improve one's health. Studies have shown that mice experience benefits such as longer lifespan, increased insulin sensitivity and stress resistance when fed an extremely low-calorie diet (usually two-thirds of the typical calorie-count).

But recently, researchers have discovered that fasting may be just as good for health as cutting back on calories. A new study published in the May 13, 2003 issue of the Proceedings of the National Academy of Sciences showed that mice that were starved every other day, and otherwise allowed to eat as much as they wanted, received many of the same health benefits as mice that had their daily diets curtailed. Mark P. Mattson, chief of the National Institute on Aging's Laboratory of Neurosciences and lead author of the study, told Reuters Health, "The mice are better off on a diet where they eat fewer meals than when they have continuous access to food." According to Mattson's study, this is true even if the mice that can eat whenever they want are kept on a reduced-calorie diet.

Past studies have suggested that substantially cutting calories increases lifespan and reduces the risk of age-related diseases in animals. A 14-year study that was first reported in May 2002 in the Journal of the American Veterinary Medical Association, showed that dogs that are fed a restricted diet live an average of 1.8 years longer than dogs that eat more. Many of these previous findings were attributed to a long-term reduction in calories. The difference with the mice in the fasting study is that their calorie intake was no less than it would have been under normal circumstances. Though they ate nothing on the fasting days, they ate twice as much as normal on the feeding days.

The fasting study took place over five months with three groups of mice. One group was forced to fast every other day. In between fasting days, the mice were allowed to eat whatever they wanted. They tended to stuff themselves on the eating days, making up for lost time. Another group was allowed to eat whatever it wanted every day. These two groups ended up eating the same amount. The final group was put on a diet with 40% fewer calories than the others.

At the end of five months, Mattson and his team measured the mice's blood sugar and insulin levels. Both the fasting and restricted-diet mice had lower concentrations of blood sugar and insulin than the mice that were allowed to eat whatever they wanted. This put the first two groups of mice at a lower risk of diabetes, a disease that affects the ability to use or produce insulin, a hormone that regulates the body's use of glucose, a simple sugar. But the fasting mice had even lower insulin levels than the dieting mice. Fasting may help mice develop the ability to metabolize glucose more efficiently. As Mattson explained to the Associated Press, "Going without food imposes a mild stress on cells and cells respond by increasing their ability to cope with more severe stress. It's sort of analogous to physical effects of exercise on muscle cells."

The researchers then injected all the mice with a neurotoxin that damages cells in the hippocampus, the part of the brain that deals with learning and memory. The researchers did this to mimic the kinds of neuronal (brain cell) damage caused by Alzheimer's disease, a debilitating disease in humans that causes memory loss and other symptoms of reduced brain functioning as people age. Fasting mice were more resistant to damage by the neurotoxin than either dieting or normal-eating mice. Eating fewer meals may benefit nerve cells by putting them under mild stress, which helps them prepare for more stress later, such as the kind induced by neurotoxins or by Alzheimer's disease.

Sources

"Meal Skipping Helps Rodents Resist Diabetes, Brain Damage." (www.nia.nih.gov/ news/ pr/ 2003/ 0428.htm) Official press release about Mattson's fasting study, from the National Institute on Aging.

"Overweight and Obesity." (www.surgeongeneral.gov/ topics/ obesity/) Fact sheets on obesity from the U.S. Surgeon General.