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August 2018

What Is Intermittent Fasting?

Maybe you’ve heard of intermittent fasting (IF). In this weight-loss method, you alternate periods of eating what you want with periods of eating little to nothing. IF is rapidly growing in popularity. But does it work? Here’s what the research shows. 

Dinner plate with an alarm clock on it and flanked by a knife and fork

Feast-and-fast eating plans

IF can take a variety of forms. These are 3 common variations:

  1. Alternate-day fasting. Every other day, you eat very lightly (about 500 calories). On the other days, you eat as you choose. 

  2. The 5:2 diet. Five days per week, you eat what you want. The 2 other days, which should not be in a row, you eat very lightly. 

  3. The 16:8 diet. For 16 hours each day, including your nightly sleep time, you have nothing but water. Then you eat as you wish for the other 8 hours. 

Weight loss, health gains?

Research on IF consists largely of animal studies and small human studies. Based on this evidence, IF may lead to weight loss—typically, 3% to 8% of body weight after 3 weeks to 6 months. 

But there’s no evidence that IF works better than a traditional weight-loss diet, which cuts calories less drastically every day. And many people may find it harder to stick with IF long-term. 

Studies have looked at possible health benefits, too. A statement from the American Heart Association concluded that IF may help:

  • Reduce triglycerides (a type of fat in your blood)

  • Lower blood pressure, but only if you lose at least 6 percent of your body weight

  • Lessen insulin resistance (the body’s inability to use insulin properly) 

As with weight loss, it’s unclear whether these improvements are long-lasting. 

Bottom line: The jury is still out on the usefulness of IF. If you’re thinking about trying it, be sure to discuss it with your doctor first.


Test your weight-loss savvy

Can you tell fact from fiction when it comes to weight-loss claims? Try this weight-loss challenge game to find out.

Online Medical Reviewer: Mercer, Nelda, MS, RD, FADA
Date Last Reviewed: 6/4/2018
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