Abstaining from food—and sometimes water—for hours or days to "detoxify" the body is the core idea behind fasting. As this practice gains popularity, experts weigh in on its safety and merits. According to the Larousse dictionary, fasting means abstaining from food, but duration is key to assessing risks. This uncertainty shapes the answer to: "Should we fear fasting?"
"There are two primary fasting approaches: intermittent fasting, limited to 24 hours and generally safe, and therapeutic fasting, which can last up to three weeks and requires strict medical oversight," explains Dr. Nicolas Zamaria, author of Your Health at the End of the Fork*. Intermittent fasting, or "fasting," involves skipping meals for 16 hours daily, such as omitting dinner or breakfast.
You might also eat normally six days a week and fast for 24 hours, stopping after lunch one day and resuming with lunch the next, as Dr. Zamaria describes. Longer fasts, spanning days or weeks, disrupt the body's balance significantly.
"Therapeutic fasting demands daily medical checks for blood pressure stability and side effects like headaches, nausea, fatigue, or irritability. Unqualified practitioners offering week-long cures is irresponsible—watch for anemia or thyroid issues," warns Dr. Zamaria.
Naturopaths are often criticized here. "Naturopathy training doesn't cover fasting supervision adequately; even specialists need medical backup for extended fasts," notes Paris naturopath Marc Le Quenven. He cautions against overhyped, expensive retreats promising miracles, which undermine credible practices. "One person's success isn't universal—beware overly optimistic claims," he adds. He favors intermittent fasting to give the digestive system a break in our overeating culture.
Short-term food restriction (never water) shows modest benefits in studies, but only with regularity and a healthy lifestyle. "Blood sugar and insulin sensitivity improve, aiding diabetes risk. Lipid profiles, immunity, and serotonin production benefit too," says Dr. Zamaria.
Therapeutic fasting's risk-benefit is murkier. Explored in Russia since the 1950s and used medically in Germany and Eastern Europe, it's not recognized in France. "Under controlled conditions, it may help skin issues, asthma, allergies, hypertension, or early diabetes, but small studies limit conclusions," Dr. Zamaria cautions.
Fasting for weight loss risks muscle loss over fat, with quick regain.
(*) Ed. Marco Pietteur, 28 euros. Royalties support Institut Pasteur research.
