Make way for readers | Demystify science

Each week, our journalist answers scientific questions from readers.

Yes. But it’s unclear whether this is simply because you eat less or because of a change in metabolism, as its proponents claim.

“With intermittent fasting, you can have a modest weight loss of about 5%,” says Stéphanie Chevalier, researcher in the metabolic disorders program at the Research Institute of the McGill University Health Center. “But there are few valid studies. And so far, intermittent fasting hasn’t really been shown to help you lose weight other than by limiting the number of calories you eat. »

Intermittent fasting has several variations. You can fast every other day, or two days a week, or every day for 16 hours straight.

Cardiologist Martin Juneau of the Heart Institute, for his part, is convinced that intermittent fasting alters the metabolism.

The D^r Juneau believes that several metabolic data show that this is what happens with intermittent fasting. Animal studies support this thesis. He cites ongoing studies at the Heart Institute, and another that has shown that a combination of intermittent fasting and exercise can drop the prevalence of diabetes in a group by 40%.

A meta-analysis of studies on intermittent fasting, published at the end of 2021 in the JAMA Network Open, concluded, however, that the proof of the metabolic hypothesis is not established. “There is a lack of evidence to come to this conclusion,” says lead author of the meta-analysis, Chanthawat Patikorn, of the University of Utah.

As for the modalities, the D^r Juneau prefers 16/8 fasting. “If you don’t eat a snack in the evening, you naturally do a 12-hour fast every night. So it is enough simply to lengthen this fast. »

But be careful: you must avoid all calories during the fast. “Even half a cookie or some sugar in your coffee triggers insulin,” says Dr.^r Juneau. It blocks access to fat. »

To complicate matters, the best study on the subject, published in 2017 in JAMA Internal Medicine by researchers at the University of Illinois at Chicago, looked at alternate day fasting. Nutritionist Stephanie Chevalier believes that for a study to be valid it must have a follow-up of at least six months, and the 2017 one followed 100 people for a year.

Some people find it difficult not to eat when they are hungry. “Me, for example, I think about my breakfast when I wake up, when I’m still in my bed,” says the D^r Juneau. The study of the different capacity of one individual to another to resist hunger is embryonic, note M^me Knight. “It’s entirely possible that people are more sensitive in their brains to satiety hormones that are released when you eat,” she says.