Bob Harper: A recent study on past contestants on the weight loss reality show “The Biggest Loser” revealed that due to metabolic and hormonal changes that persist after massive weight loss, participants were burning hundreds of calories less than would be expected for someone their age and body composition — making weight re-gain almost inevitable.

Of the 14 former participants who were profiled in the study, all but one had re-gained at least some weight, and five of them were back within one percent of their starting weight from before the televised competition.

Bob Harper, a personal trainer who hosts “The Biggest Loser,” addressed the study’s disturbing findings during a segment on the “Today” show last Friday (both shows air on NBC). He proposed there might be one effective way to address the slowed metabolism that can result from dramatic weight loss: intermittent fasting.

For people who have lost weight in general, Harper advised them to continue on the diet that helped them lose weight in the first place. For example, if a person cut added sugars or highly-processed carbs, they should continue to do so in order to maintain the new weight.

But for the severely obese people described in the “Biggest Loser” study, or anyone whose metabolism has slowed dramatically, Harper also suggests intermittent fasting, which he actually follows himself. He suggested that skipping breakfast, or about 400 calories, could help them make up for the fact that their bodies are now burning hundreds of calories less than would be expected.

The increasingly popular diet could be one way to help maintain massive weight loss, he said.

What is intermittent fasting?

There are many different versions of intermittent fasting, but the basic principle behind this eating pattern is that alternating days of “feast” and “famine” can help your body shed fat, restore healthy insulin levels and perhaps even extend your life.

One popular intermittent fasting strategy is called the 5:2 fast diet. Followers eat however they like for five days, with little regard to calories or macronutrients, and then eat only 500 to 600 calories per day for two days, depending on whether they are a woman or a man. Any day can be a fast day, though the two fast days can’t be concurrent.

Harper’s personal plan restricts all consumption to a 10-hour window. First, he fasts for 14 hours (yes, sleeping counts as fasting), and then he eats two substantial meals within the next ten hours. For those two meals of the day, Harper focuses on vegetables, healthy fats, and protein. It essentially boils down to him just skipping breakfast, he told “Today” host Savannah Guthrie.

“Our bodies want to be the weight we have been for such a long time,” said Harper. “That’s why it’s such a battle; if you’ve been overweight for a long period of time, your body is going to fight you tooth and nail to get back.”

“That’s why you have to be so diligent,” he continued. “You have to watch every single thing that you are doing, no matter if you’ve lost weight on ‘The Biggest Loser,’ Weight Watchers, Jenny Craig — however you’ve lost the weight.”

Does IF work?

If book sales and celebrity endorsements are any indication, intermittent fasting is experiencing a surge in popularity — especially in the U.K., where the 5:2 fast was invented. And emerging research on intermittent fasting is encouraging. A 2015 meta-analysis of six studies that took place from 1975 to 2014 found that participants were able to lose an average of 8.9 percent of their weight after six months of intermittent fasting (this is across all types of intermittent fasting regimens). Three studies that also focused on keeping weight off found that participants were able to sustain a weight loss of 8.2 percent after one month of maintenance. Perhaps most importantly, the 20 percent participant dropout rate for those six studies was much lower than the attrition rates that usually plague weight loss studies, which can range from 10 to 80 percent.

Harper’s suggestion that people maintain weight loss with intermittent fasting is intriguing, but there is currently no scientific evidence to suggest that it would be effective in the long term, says Stephen Anton, chief of the clinical research division at the Department of Aging and Geriatric Research at the University of Florida. Anton, an expert on intermittent fasting, is not involved in “The Biggest Loser,” but he did review the “Today” show’s report.

“[Intermittent fasting] seems to be effective in producing some weight loss, because people do not compensate on their feasting days for the amount of calories that they did not eat on their fasting days,” Anton told HuffPost. “But those studies have been relatively short term, and it’s unknown what happens after the intervention is over.”

Not everyone should try intermittent fasting. Those who are hypoglycemic, diabetic or on certain medications should not fast, as prolonged periods of starvation can be uniquely damaging to them.

And like all diets, this eating pattern only works if a person can commit to following it for the rest of their life. Going off any diet can result in regained weight — and most of it in the form of body fat — so people should be cautious about embarking on diets that may be unsustainable in the long term, as Dr. Scott Isaacs of the Emory School of Medicine previously pointed out.

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