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This Is How Many Hours You Need to Fast to Lose Weight

Eat This, Not That! logo Eat This, Not That! 7/27/2020 Cheyenne Buckingham
a plate of food on a table: fasting diet © Provided by Eat This, Not That! fasting diet

It's no question that fasting is an effective way to lose weight. In fact, Patricia Bannan, MS, RDN, and LA-based nutritionist and healthy cooking expert has explained before that intermittent fasting, which is an eating pattern that cycles between bouts of eating and calorie restriction, is an especially powerful way to blast fat.

"Intermittent fasting causes glucose (sugar) concentrations to decrease and lipolysis (fatty acid oxidation) to increase significantly during the first 24 hours, which helps the body break down stored fat," she said.

However, there are many different methods of intermittent fasting, the most popular of which is likely the 16/8 method, which entails skipping breakfast and eating between an 8-hour time frame, followed by a 16-hour fast. A new study conducted by researchers from the University of Illinois at Chicago found that fasting just a few hours of the day was enough to help people lose about 3% of their body weight in roughly two months.

The study, which was published in the journal Cell Metabolism, compared the results of two different time-restricted feeding diets, where participants were asked to fast for 20 and 18 hours, respectively.

"This is the first human clinical trial to compare the effects of two popular forms of time-restricted feeding on body weight and cardiometabolic risk factors," said Krista Varady professor of nutrition at the UIC College of Applied Health Sciences.

Here's how it worked. Those who participated in the 20-hour fast ate whatever they wanted between 1:00 p.m. and 5:00 p.m. and for those who were assigned the 18-hour fast were allowed to eat until 7:00 p.m. During the fasting periods, participants were allowed to drink water as well as other calorie-free beverages. The control group was asked to maintain weight and not make any changes to their diet or physical activity levels.

The result? After 10 weeks, participants in both fasting groups reduced their caloric intake by about 550 calories a day, enabling them to drop (on average) 3% of their body weight. In addition, researchers also discovered that both insulin resistance, which can lead to type 2 diabetes, and oxidative stress levels were reduced in those who fasted in comparison with those who didn't in the control group.

In short, both fasting periods were effective and lead to nearly identical weight loss results.

"The findings of this study are promising and reinforce what we've seen in other studies—fasting diets are a viable option for people who want to lose weight, especially for people who do not want to count calories or find other diets to be fatiguing," Varady said. "It's also telling that there was no added weight loss benefit for people who sustained a longer fast—until we have further studies that directly compare the two diets or seek to study the optimal time for fasting, these results suggest that the 6-hour fast might make sense for most people who want to pursue a daily fasting diet."

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