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Published on June 08, 2021

Intermittent fasting can have unintended consequences

Intermittent Fasting

The term ‘intermittent fasting’ is not new, but one particular version of it, called ‘time-restricted eating,’ is currently quite trendy. Facebook has many ads for this phenomenon and it’s a good bet you know someone who has given it a try. But the eating method may backfire for those who are doing it to lose weight.

The idea of the eating regimen is that you limit your food and calorie intake to certain hours of the day and fast for the rest of the time. For example, some people eat just between the hours of noon and 8 p.m. That means they are fasting for 16 hours.

A recent study published in JAMA Internal Medicine warned that people who adhere to this diet may be getting the unintended result of losing lean body mass. The study included 116 people who were either overweight or obese. The time-restricted eating group was instructed to eat all their calories for the day between noon and 8 p.m. and then refrain from consuming any calories from 8 p.m. until noon the next day. The control group was instructed to eat three structured meals a day.

At the end of 12 weeks, the time-restricted group had lost an average of two to three pounds. The control group lost an average of one- and one-half pounds, which is not a significant difference. But 65 percent of the time the restricted group’s weight loss was from lean body mass.

The study was a valid one, said Miguel Prieto, MD, an internist with Cape Cod Healthcare’s Bourne Primary Care.

“If you restrict the number of calories that you eat, you will certainly lose a lot of muscle mass,” he said. “That will happen first because you are going into a catabolic state. You will eventually lose the fat tissue, but it’s better if you are exercising and you are not starving but just restricting the calories.”

That’s the beauty of a plant-based diet, he said. You can get a lot of nutrients with a very small number of calories. When he recommends a plant-based diet to his patients, he compares it to an all-you-can-eat buffet, which he said is a good hook. Restricting calories can also have another positive effect.

“Calorie restriction is associated with longevity, there is no question about that,” he said. “No matter which animal they tried it on, when they restricted the calories, each subject lived significantly longer.”

He points out that people who live in what are referred as the Blue Zones, with the highest concentration of people 100 years or older, all have certain things in common. Not all of these regions of the world eat plant-based diets, but they do eat a lot of fruits and vegetables. They don’t eat large amounts of food and they all have low stress levels.

High levels of stress are associated with increased hunger, he said, because the body releases cortisol and adrenaline. When you eat, you stimulate what is known as the ‘vagal effect’ on your body, that counteracts the release of adrenaline and cortisol.

Most of the fasting diets are not sustainable because most people cannot fast for years on end, said Dr. Prieto. For those who do want to try a diet of intermittent fasting, he does not recommend eating during the time window of the study.

“Based on what I know about from the studies, the best time to suppress your eating is not breakfast,” he said. “So, if you want to eat in an eight-hour window, you start eating in the morning and stop eating around 2 p.m. Shifting to eating earlier in the day instead of late at night certainly increases weight loss because even if it’s the same amount, if you eat it at certain times of the day it has an effect on your metabolism and whether you will promote fat tissue formation or not.”

His best advice is to eat early, eat less and eat more plants.