Fasting has become an increasingly popular form of weight control in recent years, although the practice of dietary restriction has been around for centuries. The idea is an ancient one, especially among religious orders, but the ways of practising fasting have evolved over time and continue to evolve.
In recent months, a form of fasting called "16/8 intermittent fasting" has gained many new followers. As the name implies, it consists of not eating for 16 hours, followed by eating regularly for the next hour hours. The most popular schedule consists of eating normally from midday to 20:00 and then not ingesting anything until noon the next day.
Jean-Paul Thissen, head of the endocrinology and nutrition department at the Cliniques Universitaires Saint-Luc in Brussels, is one of many experts who balance their acceptance of the benefits of fasting – specifically, weight loss and reduction of body fat – with a healthy dose of caution. He advises anyone considering starting a fasting programme to do extensive research first.
"There are two mechanisms at play in these fasts," he told Le Soir. "Not eating for several days or several hours will first have the effect of lowering insulin levels. This promotes what is called autophagy, a process of cleaning cells.”
Daylight and power supply
"The second mechanism at work during a fast is that of resynchronisation between a central clock specific to the body and dependent on daylight on the one hand, and the power supply on the other," Thissen explained.
"It's more complex but put simply, this synchronisation is important because it is light that allows the brain to send nerve and hormonal signals to a series of tissues, which prepares them to receive food. Without it, they are not ready. This, it is thought, increases obesity problems.”
"But be careful," he added. "Weight loss is not due to this second mechanism alone. When you can eat during an 8-hour period exclusively, you ingest less as well.”
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Thissen believes that this belief in fasting as a way to lose weight will continue to popularise programmes such as 16/8 but for how long, it is hard to say.
“I don't know if intermittent fasting will stay in vogue for much longer,” he concluded “But what will remain, it seems to me, is the attention now paid to nycthemeral rhythms, and not eating at all hours of the day and even night.”
