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Is Fasting the Best Way to Lose Weight and Boost Health?

New research explores the potential health benefits, and risks, of intermittent fasting

By Winnie Yu | February 1, 2013

Dave Williams had struggled with his weight for years until he finally found a method that worked.
 
Last June, the 57-year-old chief financial officer from Cordova, Tenn., began intermittent fasting, which involves consuming no more than 400 calories during a pair of 16-hour periods each week. For Williams, this means that every Saturday and Wednesday night, he stops eating at 10 o'clock. Then, with the exception of water and a scoop of protein powder the next morning and midafternoon, he doesn't eat a thing until 4 p.m. the next day. (He eats normally the rest of the week and is not following any other diet program.)
 
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After five months, Williams has dropped 10 pounds, lost his love handles and lowered his blood pressure.

While fasting, "you learn that food is not that important, and that you can choose not to eat for a period of time," he says. "I find that the fast days are more productive since I don't have to worry about breakfast or lunch. You feel hungry at times, but you also feel in control."
 
A Potential Range of Benefits
      
Mark Mattson, chief of the laboratory of neurosciences at the National Institute on Aging and a committed faster himself, has spent 25 years researching the effects of fasting and calorie restriction, in which people reduce their daily food intake to as much as 30 percent below the 2,200 calories a day most active adults average. (People following a calorie-restriction regimen often consume less in the course of a week than those who intermittently fast.)

In the 1990s, he and his colleagues found that mice placed on an alternate-day fast for three months appeared to be shielded from such degenerative conditions as Alzheimer's, Parkinson's and Huntington's disease. More recent animal research suggests fasting may offer protection from major neurological disorders as well.

"In animal studies in my lab and by others, intermittent fasting imposes mild but beneficial stress on nerve cells and they respond adaptively," Mattson says. "They respond by being better able to cope with additional stress."

Mattson has found that nerve cells during a fast behave much like muscle cells do during exercise. "Both are excitable cells," he says. "When they're active, they're under mild stress from being active, and there's increased energy demand."
 
During intermittent fasts — and exercise — Mattson has found an increase in production of the protein called brain derived neurotrophic factor. Critical for learning and memory, it protects neurons from being damaged or destroyed by substances like the amyloid protein that clumps together as plaque in the brains of Alzheimer's patients.

By stressing out the nerve cells, intermittent fasting forces them to work harder to sustain their energy levels and produce more mitochondria, which powers them. In challenging the nerve cells, then, fasting makes them stronger and better able to cope with stressors, like disease.
 
Neuroscientists often cite the principle of "use it or lose it," the idea that if we don't keep our brains sharp and engaged as we age, through exercise, work, music or mental challenges, like crossword puzzles, we risk losing our mental agility or "plasticity." Intermittent fasting may turn out to be another way to ward off that decline.

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Additional research has shown that sharply reducing caloric consumption promotes longevity, at least in mice. "Calorie restriction is the most powerful intervention to slow aging and increase life span in experimental animals," says Luigi Fontana, a professor of medicine at Washington University in St. Louis.
 
Other experts are skeptical of claims that fasting could have neurological benefits. "The only data that I am aware of in this area is from limited studies done in animals showing that caloric restriction may retard some of the processes of aging," says William Thies, chief medical and scientific officer for the Alzheimer's Association. "As a clinical intervention to reduce Alzheimer's disease, it is hard to give it much credit at this point. Much more research is needed."
     
A Fasting Primer
 
Mattson practices what he preaches, following a form of intermittent fasting each week from Monday through Friday. To further explore the effects of intermittent fasting on human brain health, he is planning a study of women age 55 to 70 who are overweight and insulin resistant. The subjects will do intermittent fasting for two months; researchers will determine if the regimen produces any changes in the brain.

Mattson emphasizes that more studies like his will be necessary before he or anyone else can make a clinical recommendation of intermittent fasting to the general public. There are certainly populations for whom fasting would be discouraged in any event, including young children, teenagers and adults who are underweight, pregnant women and frail, older adults.

Current theories and studies of intermittent fasting are primarily focused on the potential benefits for the overweight. People who maintain a healthy weight and diet should keep in mind that their daily approach probably already delivers many of the advantages they might get from intermittent fasting. If you have any doubts about beginning a fasting regimen yourself, consult your doctor.

(MORE: One Man's Diet: How I Lost Nearly 50 Pounds)

Those who begin intermittent fasting can expect to feel hungry and may even experience some headaches at first. But for most people, those side effects ease up after the first couple of weeks.
 
While fasting, it's still vital to make healthy choices when you eat. "I don't believe you can eat whatever you want one day and fast the next day," Fontana says. "Calorie restriction also means optimal nutrition. If you're restricted one day and eating a hamburger, French fries and a sugary beverage the next, you will end up with malnutrition."
 
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