Is fasting good for your health, yes or no?

It increases life expectancy, helps fight cancer and eliminates toxins. These are some of the benefits of fasting, according to the sacrosanct Google. And this is only the tip of the iceberg because, nowadays, a fashion effect lends almost all the virtues to the diet. Reduction of cardiovascular diseases, renewed tone, boost of the immune system… For a few, we would not be surprised to read that this age-old practice allows, among other miracles, to boost hair regrowth. This shows that fasting today crystallizes all fantasies.

But basically, what do the followers say? And above all: what does science think? After all, we could well be dealing with a vast hoax. Reason why with his documentary Fasting, at the crossroads (2019), Fabien Moine, who presents himself as a “naturopath-hygienist” and “health educator”, goes to meet doctors and amateur “fasters”. The objective? Take stock of our knowledge on the therapeutic scope of the diet. But with an approach whose impartiality leaves one wondering, in view of the professional activity of the director: his personal site sells online training courses, including one entitled “How to succeed in your fast” for the sum of 199 euros. Focus.

“Even if there is fatigue and some dizziness, after stopping eating for several days I felt good, really good even”enthuses a faster. Which, through its practice, is part of a surprisingly old tradition. After all, already in the 5th century BCE, the famous Ancient physician Hippocrates recommended fasting in place of medication. On a more spiritual than medical level, Buddhism also prescribes fasting. As well as the Christian (Lent), Judaic (Ykippur) and Muslim (Ramadan) religions.

In short, as counterintuitive as it may seem, the idea of ​​forbidding yourself to eat to feel better is quite old school. But what are we talking about, exactly? As a result of the trend, fasting today comes in all flavors. For the sake of summary, let us simply cite the dry version (no food or drink), water (no food, but liquids are allowed) and intermittent (no ingestion, but only part of the day). “The objective is to activate the body’s compensation mechanisms”asks an intervening doctor. Before unrolling: “The glucose we ingest functions as a brain nutrient. So when we fast, the body must find it elsewhere. In the liver first, then by making it from fatty and amino acids”. The diet becomes dangerous when the metabolism falls so short of glucose that it is forced to melt muscle mass. Creepy?

Concerning vigilant and supervised fasting, the speaker wants to be rather reassuring. By emphasizing, in particular, that “the human body is used to food fluctuations”. After all, our “ability to overcome periods of scarcity played a role in the survival of the species”she recalls. Certainly. But, concretely: why knowingly push our metabolism towards these extremes? What's the key?

In turn, several followers parade in the documentary, weaving the laurels of what appears to be a panacea. For some, fasting has helped slow down the invasion of multiple sclerosis. Others mention the cure of invasive sinusitis, or even… the pregnancy of supposedly sterile women. Exciting testimonies, but which have not “no evidence value” underlines the author of the documentary.

In fact, all the professional doctors appearing on screen, as passionate as they are about fasting, recognize it bluntly: there is to date no scientific proof which would make it possible to establish with certainty the therapeutic interest of fasting. fasting, as confirmed by an Inserm study from 2024. But certain “healers” nevertheless recommend it, in order to treat chronic illnesses. Concerning cancer for example: we can find numerous resources indicating that the diet would “starve” cancer cells… and therefore participate in healing. But no definitive clinical study supports this lead. Worse yet: restrictive diets can potentially worsen weight loss, as well as muscle wasting. Two factors harmful to the medical treatment process for the disease, as recalled by the National Cancer Institute.

Should we therefore abandon the path of therapeutic fasting? According to Christian Tal Schaller, a trained general practitioner (now stripped of his right to practice), this would be a huge mistake. Quite simply because in the eyes of this fervent defender of unconventional medicine, which is a curious casting choice, given his conspiratorial positions towards vaccination which he compares to “a real holocaust” and the climate crisis – a “scam” in his eyes – the diet would have virtues “regenerative” that animals themselves use. In fact, many sites mention the “instinctive” use of fasting by certain species in cases of illness… but without ever citing serious scientific sources.

In a word: studies are lacking. A gap which Doctor Patrick Baqué, surgeon currently serving as dean of the Nice Faculty of Medicine, hopes to overcome. “I thought that the university needed to open up to non-conventional medicines (…) to on the one hand promote them if they are effective, but above all to fight against charlatanism which can endanger the lives of people. patients (…). This is why I want to set up a clinical study, which would consist of bringing together doctors in training so that they can evaluate the impact of an eight-day fast on themselves.”. A small-scale investigation project, therefore, which would obviously not make it possible to definitively establish proof (or counter-proof, for that matter…) of the relevance of medical fasting.

But a first step nonetheless, towards the exploration of a therapeutic path that other countries are already taking. In Russia, Germany and the United States, fasting is prescribed in a medical setting. And in parallel with this supervised mode of care, some, in their corner, devote themselves to intermittent young people in the hope of… extending their life expectancy. With the idea that a body accustomed to deprivation would be “prepared” as well as possible to face the trials of age. Good. Let the convinced be warned: those practicing a sixteen-hour-a-day diet have a 91% greater risk of dying from cardiovascular disease, according to a report from the American Heart Association, published last March.

Generally speaking, the popular and media enthusiasm surrounding fasting worries health professionals, whether in the form of a “detox cure” or for therapeutic purposes. In a press release dated March 2024, the French Association of Dietitian Nutritionists declared that they had “recently reported and alerted (…) the Ministry of Health. In particular on the problems caused by the absence in the law of the offense of “illegal practice of dietetics and nutrition” to protect users against “pseudo-nutritionists” with deviant and unfounded practices”. Conclusion of the association: “Today, the existence of the sole offense of “illegal practice of medicine” is not sufficient and effective to protect the French against this scourge (medical disinformation editor’s note) at work everywhere”.