How fast is a fast fast? No, that's not a tongue twister (though feel free to say it three times--fast!). Short-term or intermittent fasting is gaining popularity as a route to not just weight control but to potentially living a longer, healthier life. Such an eating plan includes cycling between fasting and nonfasting as well as rotating in regular periods of very low-calorie eating.
There's evidence that, in animals including rodents and fruit flies, a lifelong restricted diet that cuts calories by more than a third leads to a lifespan that's a third longer. Does it work for humans too? Scientists haven't figured that out yet, though evidence backs the idea that in people, too, eating such a calorie-limited diet leads to longer periods of good health with fewer of the diseases that typically strike in old age.
Still, who would want to deny themselves the pleasures of foods for an entire lifetime? Luckily, we don't have to. We can get the benefits of long-term fasting with daily, weekly, or monthly short-term fasts or calorie restrictions, according to recent research.
The Science Behind Going Without
Mark Mattson, PhD, who heads the neurosciences lab at the National Institute on Aging, is an expert on the science behind intermittent fasting (IF). He has contributed to a number of studies on IF and calorie-restricted diets involving both animals and humans. Results indicate that cycles of fasting may support cardiovascular health, lead to improved learning and memory and decreased symptoms of Alzheimer's, and alleviate symptoms of asthma.
Other potential benefits of IF include weight loss, improved insulin resistance, inflammation reduction, cancer prevention, boosts to brain health, and anti-aging gains.
How does it work? One theory is that fasting puts cells under mild stress. "They respond to the stress adaptively by enhancing their ability to cope with stress and, maybe, to resist disease," Dr. Mattson told the Canadian Medical Association Journal.
Approaches to IF
Unlike traditional diets, intermittent fasting is more about when you eat than what you eat. The idea is to skip or limit food for a certain number of hours in a day or a certain number of days in a week or month. Here are some common plans:
The 5:2 Plan
Eat what you normally do for five days a week, and eat just 500 calories on the other two (nonconsecutive) days.
The 16:8 Plan
Fast for 16 consecutive hours during every 24-hour period, limiting your eating to the other eight hours. For instance, have your first meal at 10 a.m. and finish your last meal by 6 p.m.
Eat-Stop-Eat
Fast for 24 hours once or twice a week.
Five Days a Month
Cut your food intake by 30 to 40 percent for five consecutive days a month, and eat as you normally do on the other days. In a recent study, human volunteers who were put on a regimen of 725 to 1,090 calories a day for five days a month lost abdominal fat, became more fit, and had lower blood glucose levels than a control group after only three months.
Convenience plan
If you can't adopt a regular mode of intermittent fasting, try fasting when it works for your schedule. Skip a meal if you're not hungry, or take a day off from eating when the time is right. You'll still get some of the benefits of a more structured plan.
Cautions
Be sure to drink plenty of noncaloric liquids while you are fasting. Water, unsweetened coffee and tea (a splash of milk or cream is OK), and other sugar-free drinks will help keep you hydrated.
Check with your healthcare provider before you make any radical changes in your eating habits, especially if you have medical conditions. People who should not fast include children, those who are underweight or have a history of eating disorders, and women who are pregnant, breastfeeding, or trying to conceive.