And many clues come from animal studies. Mark Mattson, chief of the Laboratory of Neurosciences at the National Institute on Aging in Baltimore and a professor of neuroscience at Johns Hopkins, has found, through years of longevity research, that rats and mice fed only every other day benefit in health measures like blood pressure and glucose and insulin levels. And their brains seem protected against diseases like Alzheimer's. Mattson, who began fasting himself 25 years ago, skips breakfast and lunch three or four days a week, then eats a reasonable dinner. "I go 16 to 18 hours without food," he says. "From a scientific standpoint, 10 to 12 hours after eating, I'll have completely used up what I've eaten. Then you start burning fat, and a lot of good things start happening throughout the body and brain."
When people go without food for, say, 16 hours or more, nerve cells in the brain get more active, says Mattson. He has studied the effect of that on a protein called BDNF (brain derived neurotropic factor), which plays a part in learning and memory and has an antidepressant effect. When nerve cells are more active, levels of BDNF rise, fueling the theory that fasting might delay dementia. And besides improving the glucose and insulin picture, fasting can lower levels of insulin-like growth factor, or IGF-1, a protein that encourages rapid division of cells. In adults, too much IGF-1 appears to lead to accelerated aging and cancer, says Mosley.
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Nutrition researchers have wondered for decades if drastically cutting calorie intake overall might extend life, as it does in animals. That has yet to be proven, though the practice clearly affects markers of aging. Luigi Fontana, a professor of medicine at Washington University in St. Louis, has studied members of the Calorie Restriction Society, who eat about 30 percent fewer calories than normal in an effort to live longer. A 2007 review of his and other studies shows that after an average of six and a half years on the restricted diet, members had greatly reduced their risk factors for heart disease and diabetes. Eating much less every day, Fontana has found, lowers inflammation and results in a more elastic left ventricle – a "younger" heart – and helps reduce the incidence of many cancers associated with obesity.
But the problem with consistently low-calorie diets is that most people can't stand the ongoing deprivation. Fontana is launching a pilot study of 40 people to see if 500 or 600 calories two to three days a week can mimic the effects of a very-low-calorie daily diet. Mattson is also preparing a small study to see if intermittent fasting affects early markers for cognitive decline among obese insulin-resistant people aged 55 to 70. Meanwhile, especially in light of the research supporting breakfast, it's wise to check with your doctor before trying fasting.
The most controversial idea to arise in the recent media storm about the practice is that people can eat whatever they want on nonfasting days. Experts warn that low-calorie days should be packed with nutrients, and that fasters should maintain a proper balance on normal days, too.
Maggie Bass's total cholesterol is still high, but has dropped from about 266 to 243 since she changed her eating pattern. The weight has come off slowly – about a pound a week. Can she keep it up? Time will tell, but she has stuck with fasting for longer than any diet she's tried before.