Any benefits to intermittent fasting diets?

Ask the doctor

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Q. I have read about diets that involve fasting for one day, followed by normal eating for the rest of the week. Are there any benefits to this kind of diet??

A. Most diets achieve weight loss through the same equation—a reduction in total daily calories consumed in relation to the calories needed to maintain your weight.

Intermittent fasting does this by severely limiting calories for one or two days per week (either by not eating and drinking only water or reducing calories to 600 per day), followed by a less restricted diet on the other days. There are other variations, but this is the most common approach.

The theory is that the diet decreases appetite by slowing the body's metabolism. Does it work? Studies of intermittent fasting have been limited to several months in duration, so the long-term benefits or risks are unknown. The approach does appear to achieve weight loss similar to other diets. However, it is not superior to other calorie reduction plans and there is no proof that intermittent fasting has other benefits, such as disease prevention or the ability to slow aging.

If you are considering this type of diet, make sure to discuss it with your doctor. Skipping meals and severely limiting calories can be dangerous for people with certain conditions like diabetes. People who take diuretics for blood pressure or heart disease also may be more prone to electrolyte abnormalities from fasting.

—William Kormos, MD
Editor in Chief, Harvard Men's Health Watch