Intermittent fasting: Fact-based weight loss strategy, or fruitless fad?

Nutritionists say there are some benefits of fasting on and off to loose weight — when it's done right, But they caution that there also dangers to intermittent fasting, and that some claims are not backed by science.
Nutritionists say there are some benefits of fasting on and off to loose weight — when it's done right, But they caution that there also dangers to intermittent fasting, and that some claims are not backed by science. (Illustration)

A nutritionist from University of Maryland Medical System regularly provides a post to the Picture of Health blog. The latest post is from dietetic intern Avital Schwartz.

Intermittent fasting is a newer type of diet that some claim helps people lose weight and improve their health. But does it actually work?


It depends on how it’s practiced. When done correctly, it can be beneficial. Done incorrectly, not so much

But what exactly is intermittent fasting, and how does it work?


Intermittent fasting – also called “alternate day fasting” or “intermittent energy restriction” –consists of eating very little or nothing at all on certain days of the week or times of the day.

Types of intermittent fasting

  • The 5:2 system. With this method, you fast any two non-consecutive days of the week. On fasting days, you either consume nothing at all or limit yourself to about 500 calories. The other 5 days of the week, eating isn’t restricted.
  • The 20-hour daily fast. This fast ends with one big meal each evening. During the 20 hour fasting period, raw fruits, vegetables and some lean protein is allowed.
  • The extended overnight fast. In this version, you lengthen your overnight fast to last 14 hours. In other words, you fit your regular meals into a span of 10 hours and fast for 14 hours overnight. This way most of the fast occurs while you’re sleeping -- painless!
  • Alternate day fasting. This consists of eating regularly one day, 20% of your normal intake the next (about 400 calories), and repeating that pattern continuously.

Intermittent fasting: fact or fad?

Now that you know the popular types of intermittent fasting, you might be wondering if there are any proven benefits, or if it’s just another fad. As usual, both are true. There are some true benefits to fasting as well as some dangers, and some claims are not backed by science.

Based on studies over the past two years from the National Institutes of Health and the American Journal of Clinical Nutrition, when done correctly, fasting can have positive benefits. Intermittent fasting has been linked to decreases in weight, LDL cholesterol, triglycerides, and inflammation. Diabetes, heart disease, and blood sugar levels were also lowered in people who fasted. Fasting was not linked to significant fatigue or mental impairments either. And, contrary to what you might think, fasting one day did not lead to over-eating the next.

Not all results have been positive though. Fasting every other day, or going too long without food, led to serious starvation-like effects, such as muscle loss, heart and organ damage. People also stayed hungry while they fasted, no matter how long they kept up the diet.

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What fasting approach should I choose?

Most research agrees that the best type of fasting is the extended overnight fast. In a 2007 study on breast cancer survivors, those who fasted more than 13 hours overnight were less likely to have a recurrence of cancer. This study supports other research showing that spreading meals and snacks over no more than 10 hours each day is beneficial. A 14-hour fast is easy to fit into your day. If you finish dinner at 7:00 pm and don’t eat breakfast until 9:00 am, you’ve fasted for 14 hours. So simple!

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Finally, all studies concluded that consistent calorie restriction yields the same overall results as intermittent fasting. In other words, eating a smaller amount of calories every day (say, 1500 instead of 2000) is just as beneficial as fasting.

So, whether you decide to try intermittent fasting or simply make a habit of choosing smaller portions, both are healthy choices.

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