Just a quick search on the internet to find several ads for websites and apps that promise weight loss through intermittent fasting, a method that limits eating to periods ranging from 6 to 8 hours a day.
There are several models of intermittent fasting: in the most common, the person stays 16 hours straight without eating and eats for the remaining 8 hours, with low glycemic index foods. There are regimens that institute fasting for 14, 24, and even 36 hours.
According to proponents of the regimen, spending many hours without eating accelerates metabolism and promotes rapid fat burning, even helping to reduce the risk of diseases such as diabetes and metabolic syndrome.
Studies with mice and small groups of humans have reinforced the idea that restricting food to a few hours a day would help you lose weight, but there is debate in the scientific community as to why the weight is lost.
Would people who follow intermittent fasting lose fat because they go long hours without eating or because, with the time restriction, they start to eat fewer calories, as in other diets?
A rigorous study conducted in China over a year of 139 people and published this week in the New England Journal of Medicine appears to have ended the discussion. According to the data found, there is no difference between the intermittent fasting regimen and other calorie-restricted diets.
The study participants, the largest and longest on the subject, were divided into two groups. The first followed a diet of 1500 to 1800 calories (men) and 1200 to 1500 calories (women), and the second adopted the same diet, but with a restriction: the participants could only eat from 8 am to 4 pm, concentrating the intake of all calories allowed in 8 hours.
The first group lost about 8 kilos, on average, during the 12 months; the second, 6.3 kilos, a difference considered irrelevant. Other parameters such as waist circumference, BMI, body fat and lean mass ratio, blood pressure and other risk factors for metabolic syndrome were also measured, and no significant differences were found between the two groups.
According to the authors of the study, patients with obesity who undergo regimens that limit the intake time do not obtain more benefit than those who adopt other calorie restriction regimens.
Another study carried out with 116 people and published in 2020 also revealed no difference between intermittent fasting and other regimens. The researchers followed, for 12 weeks, 116 people who were separated into two randomized groups. The first had three meals a day, without caloric restrictions, and the second was able to eat at will, as long as he did it between noon and eight at night. There was no major difference in weight loss between the two groups.
Nutritionist Fernanda Imamura says that the study released this week corroborates other scientific evidence. “There is no weight loss benefit when comparing intermittent fasting and other calorie restriction regimens,” she says. For the expert, fasting can lead to weight loss, but thanks to caloric restriction, and not because it promotes faster fat burning.
While some people, especially those who have difficulty counting calories, can adapt to intermittent fasting, it shouldn’t be for everyone. “Complaints of malaise, weakness and nausea are common among people who do intermittent fasting. In addition, restriction can serve as a trigger for compulsions and eating disorders, especially in adolescents”, explains Fernanda.
New diets appear every day that promise rapid weight loss. However, studies show that those who lose weight slowly and gradually are more likely to not regain it. In addition, as nutritionist Fernanda Imamura explains, the focus of food should always be health, not caloric restriction. For this, it is necessary to establish a healthy relationship with food, so that we can make better food choices and with more autonomy.
Giving preference to fresh foods, choosing foods of good nutritional quality, establishing amounts that respect the limits of hunger and satiety, and performing physical activity regularly are still the best way to maintain health.