Lately, it is undeniable that the practice of intermittent fasting to lose weight is in vogue. According to the Spanish Society of Endocrinology and Nutrition (SEEN), this occurs after staying without eating during the night, between 8 and 12 hours. It is what is considered a 'physiological fast'.
"If we talk about 'voluntary fasting' we can find different situations, such as 'intermittent or sporadic fasting', the most common being daily (at least 12 hours of fasting), and weekly (one or two days a week , not in a row)", notes the SEEN. In contrast, the water fast or Buchinger fast is less well known. This is a medically supervised fast, popular in Europe, in which people consume only a small amount of juice and soup per day.
Now, a study from the University of Illinois Chicago (United States) suggests that water fasting - in which you consume only water for several days - can help you lose weight, but it is not clear how long it is maintained. In addition, the other metabolic benefits of water fasting, such as lowering blood pressure and improving cholesterol, appear to disappear soon after the fast ends, according to the researchers.
However, there do not appear to be any serious adverse effects for those who do a water fast or a similar type of fast in which a very small number of calories are consumed per day, according to Krista Varady, a professor of kinesiology and nutrition, who led the research. , which is published in 'Nutrition Reviews'.
"My general conclusion is that I suppose you could try, but it seems like a lot of work, and all those metabolic benefits go away," Varady said. She has stressed, however, that no one should undertake one of these fasts for more than five days without medical supervision.
Varady, an expert in intermittent fasting, explained that she wanted to study fasting in water because suddenly last fall she began receiving contacts from journalists who wanted to know her opinion on it. She thought that if she was going to comment, she should investigate the published studies on the matter.
The new work is a bibliographic review of eight investigations on fasting with water. Varady's team analyzed the results of each of those studies to see what effect they had on weight loss and other metabolic factors.
The researchers found that fasting seemed to stimulate noticeable weight loss in the short term. People who fasted for five days lost between 4 and 6 percent of their weight; those who fasted between seven and 10 days, between 2 and 10 percent, and those who fasted between 15 and 20 days, between 7 and 10 percent.
Only a few studies in the review followed up on whether participants regained their lost weight after the fast had ended. In one of them, people recovered in three months everything they had lost in a five-day water fast. In two other studies, only a small part of the lost weight was regained, but these studies encouraged participants to restrict their caloric intake after the fasts ended.
Instead, it was clear that the metabolic benefits of fasting disappeared soon after the end of the fast. The improvements in blood pressure, cholesterol, and blood sugar levels were short-lived, returning to baseline levels soon after the participants started eating again.
Some of the studies included participants with type 1 and 2 diabetes, who did not experience ill effects from fasting, although they were closely monitored and had their insulin doses adjusted while fasting.
The most common side effects of these prolonged fasts were similar to those of intermittent fasting, according to Varady, such as headaches, insomnia and hunger. No serious negative effects, such as metabolic acidosis or death, were observed in the studies.
He did observe that participants in these extended fasts lost about two-thirds of their weight in lean mass and one-third in fat mass. This is the opposite of what happens most of the time during weight loss, where more fat is lost than muscle. It makes sense that these extreme fasts would have this result, he says, because the body needs a constant supply of protein. "If you don't have that, then you go to muscle," she said.
Varady's research on intermittent fasting has focused on the effectiveness of this regimen for weight loss, as well as specific questions, such as whether intermittent fasting affects fertility. Varady says she would encourage someone hoping to lose weight to try intermittent fasting instead of a water fast, "because there's so much more data to show that it can help with weight control."
