Although research is inconclusive and experts have differing opinions, some say intermittent fasting is key to weight loss.

A concept that was once primarily restricted to religious practices has infiltrated the diet world and is rapidly gaining popularity in the U.S.

Though research thus far is mostly inconclusive and experts hold conflicting opinions, intermittent fasting — abstaining from all or some kinds of food for a duration — may be beneficial for weight loss.

Bethany Diggett, a registered dietitian with Kansas University Hospital, shared some of the potential benefits of fasting.

“As far as weight loss, (fasting) makes us use the stores that we have as energy instead of constantly replacing energy, and then also it can recycle some of your immune system cells,” she said. She also noted that it “definitely” helps burn fat, but said research is unclear about whether it also helps build muscle mass.

Diggett recommends two different methods of fasting to patients. The first is a 12- to 14-hour fast, the majority of which falls overnight. She said she uses this method herself.

She shared how she recommends this method to patients who are healthy, but looking for a little bit of weight loss.

“I just explain that it’s good to let our body fast and burn up the stores that we have, and I kind of explain what I do,” she said. “I make sure I don’t eat from 7 at night to 9 in the morning, and so that’s 14-hour fasting. That’s if someone wants to lose maybe 5 or 10 pounds.”

The second method Diggett suggests is called the 5:2 diet — eat normally for five days of the week and fast for the other two. Those two days can be consecutive or spread throughout the week.

“On the nonfasting days, those five regular diet days, they can eat anything, but we do encourage them to follow an overall healthy diet with a low glycemic index, so focusing on fruits, non-starchy vegetables, whole grains, beans and lean protein,” she said.

She said most commonly on the two fasting days, the calorie allotment is 500 for women, 600 for men, and that can be consumed in one meal or in little portions over the course of the day.

“On those fasting days they can drink as much water as they want and then non-calorie liquid, like green tea, black coffee or artificially sweetened beverages,” Diggett said.

For those who are getting in shape but hit a plateau and the scale won’t budge, Diggett said the 5:2 plan could “kickstart” the body into burning some of its stores.

On the other hand, Kelsey Fortin, a health educator with Watkins Health Services at Kansas University, said she preaches healthy behavior changes and sustainable diets — a bill she says fasting doesn’t fit.

“You may see that you experience weight loss for a short period of time, but typically you engage in what’s called yo-yo dieting where you’ll lose an amount of weight for a certain period of time while you’re engaging in the fasting diet, but the second that you get off of it you’re gonna gain that weight back,” Fortin said.

Extremely restrictive diets can be dangerous, Fortin said, and should be monitored closely by a doctor or dietitian to make sure the patient is getting enough food to sustain daily life and avoid fainting and low blood sugar. She also said it can cause adverse effects.

“If my body is restricted too much, it’s going to cause my metabolism to slow because the best way to speed up my metabolism is to be constantly eating,” she said. “So I want to be eating within what my calorie expenditure is, absolutely, but I need to be mindful of the fact that my body needs to keep on running, keep on burning through that.”

Diggett acknowledged potential risks for fasting as well, particularly for people who have other health problems. Diabetics, for instance, face a higher risk of hypoglycemia.

“We definitely encourage patients that, if they want to start a diet like this, to talk to their health care provider or get a dietitian on board to help them through it and make sure it’s safe for them,” she said.

She also noted that the reason she recommends eating 500 calories on fast days is because your blood sugar could drop over two days with no food.

“If you’re having about 500 calories a day, you could have 100 calories maybe every two hours and that should get you through the day without passing out or becoming malnourished,” she said. “That can’t happen in just fasting for two days a week.”

Another risk Diggett mentioned was binge-eating, which she said is especially a concern for patients on the 5:2 diet who do their two fast days each week back-to-back.

“We see binging on that day after the fasting, so they’ll eat more than they normally would have ever in a day before they started the 5:2 diet,” she said. “So that’s always a concern.”

Diggett does preach the same balance Fortin favors.

“As a dietitian, in addition to some of these new little fad diets that come out, we just really always preach an overall healthy, well-balanced diet; consuming healthy foods in moderation … paired with a good physical activity regimen,” she said. “That’s always the best bet as to attaining and maintaining a healthy weight.”

Fortin said the methods she teaches KU students include eating whole grains, avoiding saturated fats, staying within calorie parameters for their personal goals, and looking at healthy weight loss of 1 to 2 pounds per week while engaging in regular physical activity.