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Is Intermittent Fasting Effective for Weight Loss?

A growing number of people are turning to fasting, either on certain days or during certain hours, to promote weight loss and improve health. Here’s what you need to know before trying it.


THE CLAIM: Fasting diets are a good way to lose weight.

Over two thousand years ago, the Greek physician Hippocrates extolled the virtues of fasting. Today celebrities and others are embracing the practice as a way to lose weight and improve health. The form they promote, sometimes called intermittent fasting, involves periods of little or no food alternated with periods of normal eating. While there’s some science behind fasting diets, anyone who says they’re a sure thing is playing fast and loose with the truth.

Intermittent fasting comes in several forms, including the 5:2 diet, which involves consuming only 5 or 600 calories two days a week and eating normally the other five days;

Alternate-day fasting, in which you take in 500 or fewer calories every other day;

And time-restricted feeding, which entails eating during a several-hour window and fasting the rest of the day.

In lab animals, fasting protects against conditions such as cancer, heart disease, and diabetes, improves brain function, and increases lifespan.

Researchers theorize that the benefits may be due to a built-in survial mechanism that makes animals heartier when food is scarce. Decreases in insulin and inflammation, which occur during fasting in animals as well as people, may also play a role.

But whether fasting prevents disease and prolongs life in people is an open question because there haven’t been long-term studies.

As for weight loss, research suggests that intermittent fasting may be effective, but not necessarily more effective than standard calorie-cutting diets.

One possible pitfall is the temptation to pig out on normal eating days, which obviously can undermine your weight loss efforts.

Fasting diets are not a good idea for pregnant women, people with diabetes or eating disorders, or those who take certain medications.

Otherwise, if you can handle eating very little or nothing for long stretches, it may be okay to a follow a fasting diet. But like other fad diets, it’s not a proven long-term solution to weight control. That requires permanently changing what you eat. Despite all the claims, there are, unfortunately, no fast answers.

For more on diet and nutrition claims, check out my book, Coffee is Good for You, which reveals the truth about everything from red meat to red wine.

Helping you be a healthy skeptic, I’m Robert Davis.