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Is intermittent fasting worth it?

A woman in a grocery store looks at produce.

Is fasting the fast track to weight loss?

Jan. 30, 2020—Intermittent fasting is a diet trend that's getting a lot of attention lately. It involves rotating periods of eating with periods of fasting.

Advocates recommend it for managing weight loss, heart disease, type 2 diabetes and problems sleeping. And there is evidence that intermittent fasting may help regulate glucose levels, reduce inflammation, improve cholesterol levels and help manage blood pressure.

Unfortunately, most of the studies on intermittent fasting have been conducted on animals, on small groups of people or over short periods of time. So not a lot is known about the long-term effects.

But here's a quick look at what the science says about three popular fasting methods:

Alternate-day fasting

As the name suggests, alternate-day fasting involves fasting every other day. On fasting days, no foods or beverages with calories are consumed. Drinks such as water, black coffee and tea are OK. On non-fasting days, you can eat what you want—although it's still a good idea to follow a healthy eating pattern.

According to the Academy of Nutrition and Dietetics, studies have found that the amount of weight lost following an alternate-day fast was equal to that lost on a typical low-calorie weight-loss plan. However, fasting may be a more difficult plan to follow for most people. It can cause serious hunger pangs and difficulty concentrating on fasting days.

In a research review published in the New England Journal of Medicine (NEJM), one study showed no improvement in cholesterol and blood pressure with alternate-day fasting. Another showed short-term improvements in heart health that go away when a typical diet is resumed.

Modified fasting

Modified fasting involves eating very little food on fasting days. Some people restrict their intake on fasting days to as little as 20% of needed calories. Others limit themselves to only 500 calories on those days.

One version of modified fasting is called the 5:2 fast. On this plan, people fast two days a week and follow their regular diet for the other five days.

According to the Academy of Nutrition and Dietetics , some studies have found no significant difference in weight loss on a modified fast versus a traditional weight-loss diet.

But the NEJM review noted that improvements in insulin sensitivity and waist size have been observed on the 5:2 fast.

Time-restricted fasting

This kind of fasting restricts eating to certain times of day, with the goal of fasting anywhere from 12 to 18 hours a day. Much of the fast occurs while you're sleeping. This may be an easier fasting pattern for people who don't snack after dinner or eat breakfast first thing in the morning.

There's little research on the effects of this type of fasting in humans. But the NEJM review noted one study in which young men who fasted 16 hours a day and did strength training lost fat while maintaining muscle mass over two months.

This kind of fasting also has risks. For instance, people who fast more than 16 hours a day have a higher risk of gallstones and gallbladder surgery, according to the National Institutes of Health.

What does it all mean?

While there is some promising research being done, the Academy of Nutrition and Dietetics doesn't recommend intermittent fasting as a lifestyle tool.

More research is needed first, the academy says, particularly into the negative side effects. There's a potential for nutrient deficiencies, for example. And fasting could be a risk for:

  • People with diabetes.
  • Women who are pregnant or breastfeeding.
  • Anyone with a history of eating disorders.

If you're considering fasting, talk it over with your doctor first. This is especially important if you're taking any medications that may need to be adjusted or if you have a chronic condition. Your doctor can help you understand the pros and cons—and decide the best way to move forward.

Remember: The best diet isn't a fad; it's a healthy eating style you can live with long-term. Before you jump on a diet bandwagon, take a fresh look at this tried-and-true approach to weight loss.

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