Why intermittent fasting doesn't help weight loss, according to science

An increasingly widespread method for weight loss is time-restricted eating, in which food intake is limited to a shorter period each day, this technique is known as intermittent fasting.

While debates are taking place around such strategies to lose weight or create a healthier environment, specialists from the Southern Medical University in Guangzhou in China confirmed, following research published in The New England Journal of Medicine (NJEM), that the method known as intermittent fasting has no significant benefit compared to simple calorie counting in the task of controlling or reducing weight gain.

The so-called intermittent fasting diet implies a normal daily caloric intake with the use of a short and strict caloric restriction. Meals are only consumed within a defined time during the day. They are usually used in three variants: 16/8, 18/6 and 20/4. The most commonly used is the first one consisting of a 16-hour fast and then a nutritional window of 8.

In the trial, the researchers randomly assigned 139 adults (average age 32) who were overweight or obese to some on a standard diet and others restricted in time to eat meals. All participants received reduced calorie diets (about 25% less than the initial intake recorded in the research).

For testing, the time-restricted group was asked to eat only between 8 am and 4 pm. Meanwhile, the group that had been assigned the standard diet was informed that they had no time restriction on their intake.

At baseline, the average weight of the sample population was 88 kg and the average body mass index was 32 kg/m2. As part of the research program, scientists provided substantial dietary advice and food consumption education for the members of both participating groups. To document follow-up, scientists asked study participants to keep written diaries of their intakes and photograph all the food they ate.

The results obtained by the specialists after passing the 12 months of diets assigned to the two working groups, the average weight loss was not significantly different between the standard and the one that was restricted in time (8.0 kg versus 6.3 kg). In addition, no significant differences were observed between groups in body fat, lean mass, blood pressure, lipid profile or insulin metabolism.

“The restriction of calorie intake explained most of the beneficial effects of a time-restricted diet,” said Huijie Zhang, one of the study's authors and researcher at the Southern Medical University in Guangzhou. In summary, we can confirm that the variable determining weight loss and the other variables that affect it depend on the reduction of calorie intake, regardless of the time in which food and drink intakes are distributed over time during the day.”

The renowned nutritionist Alberto Cormillot said in Infobae that “it simply doesn't work because when people go on a fasting day or half a day they eat a preventive meal, that is, they eat less before and then eat more to compensate for everything they didn't eat. For many years, it has been scientifically proven that it is advisable to eat divided during the day, at least four times. They are practices that were left aside thanks to research and the professional practice of medicine today, which accumulated knowledge and is managed with other, more serious guidelines.”

“Intermittent fasting is nothing new. At the first obesity congress held in London in 1974, I presented a paper on this practice, but after 77 or 78 I stopped recommending them. On the one hand, because those who fasted ended up eating a larger amount of food before or after the fast than they avoided. And on the other hand, because it was shown that during fasting itself there is no beneficial event for health,” Cormillot stressed in this medium.

For the specialist, these proposals “the only thing they manage to do is leave a wrong message to people, who can eat anything (bacon, chips, fried egg, wine for a period of 8 hours, total in the next 16 it purifies everything, which does not happen”.

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