We knew the high protein, Dash, acid-base or macrobiotic diets. Here is now the astro diet, which recommends eating according to the principles associated with your zodiac sign. The full moon diet, which is based on taking liquid foods on the nights when our satellite appears in its entirety. Or the DNA diet, which encourages you to choose your food according to your genes… When it comes to inventing dietary practices, the imagination of their promoters, recognized doctors or self-proclaimed experts, seems limitless. Their promises too: to lose weight of course, but also to prevent diseases, cure them or even prolong life. All these protocols, however, are not equal and some even turn out to be useless, even dangerous.
Faced with a plethoric offer, it can be difficult to disentangle the true from the far-fetched. This is the whole point of the book by nutritionist Jean-Michel Lecerf, 40 dieting misconceptions, to be published at the beginning of July (Quae). The medical director of the Longevity Health Prevention Center at the Institut Pasteur de Lille passes the 40 most popular diets through the sieve of (real) science, to help us see more clearly: “The latest fashionable diet n “It’s not necessarily the best. Some are based on beliefs, others on more rational bases, without always proving to be as promising as we are sold,” he summarizes.
Let’s first twist our necks with the many weight loss protocols. “None has proven its long-term effectiveness,” recalls Professor Lecerf. Whichever method is adopted, the loss of lean mass leads to “a reduction in basal metabolism and energy expenditure”, explains the nutritionist in his book. We will therefore regain weight more easily at the end of the diet. Rather than a substantial but time-limited deprivation of food, all the studies show that it is necessary to adopt changes step by step, by setting reasonable objectives, by durably reducing excess food and by practicing regular physical activity.
“A real business”
Messages that are difficult to get across to the general public. “The temptation is great to seek simple solutions to the complex problem of overweight or obesity. Hence the multiplication of these apparently attractive protocols, which represent a real business”, annoys the doctor. Books, consultations, food supplements and other protein powders: everything is good for shoeing the barge. Even home delivery offers for low-calorie meals, touted through advertising campaigns and television testimonials. “These ready-made menus can help raise awareness of bad eating habits, but they are generally not accompanied by any serious study”, warns Professor Lecerf.
Many of these diets claim to be based on scientific findings. What gives them an appearance of credibility. “There is often a grain of truth, but that is then diverted”, notes the nutritionist. This is the case, for example, with “low glycemic index” diets. If it can be interesting to favor foods that do not raise the blood sugar level too much after the meal, focusing on this criterion alone risks leading to aberrations. Like, in the extreme, to favor fries and croissants rather than boiled potatoes and bread, on the pretext that fats reduce the glycemic index of foods. Same with chrononutrition. Biological rhythms are certainly important: obviously, a good breakfast and a light dinner are better. But distributing the different categories of food according to the hours of the day is not necessarily a good idea: “This leads to food dissociations and restrictions through a roundabout approach”, underlines Professor Lecerf.
“Longevity” diets, gluten-free diet… and risks of quackery
“Healthy” diets are no exception to these shortcomings. Gluten-free? Often of little use in the general population. Worse still, the elimination of “fodmaps”, sugars that can cause embarrassing intestinal disorders: the list of foods that contain them is so long that it is impossible to exclude them without the help of a dietician. If the hunt for food intolerances is fashionable, this new obsession has paved the way for practices bordering on charlatanry. Therapists, most often from alternative medicine, recommend laboratory tests to look for immunoglobulins specific to different foods. “They see in the presence of these antibodies the sign that these products are not suitable for their patient, whereas in the state of knowledge, it is simply a marker linked to their consumption”, summarizes Professor Lecerf .
Another myth is that of “longevity” diets. In animals, studies have actually shown that caloric restriction prolongs lifespan. However, it is difficult to apply these conclusions to humans: “A restrictive diet experiment carried out on eight people for two years in the United States showed a drop in weight, but also in bone density, resistance to cold, libido, healing…” says Jean-Michel Lecerf. Uninviting, therefore. As for the “Okinawa regime”, named after this Japanese archipelago where there are many centenarians, it would be based on… an administrative error: “Serious studies have shown that the birth registers destroyed during the Second World War and reconstituted after the conflict have been distorted,” he said.
Whatever their methods and their motivations, all these diets pose another difficulty: the fact of opening the way to eating disorders. “For some practitioners, it’s sometimes like entering a religion. They cut themselves off from others, forbid any conviviality. We must certainly eat, but also preserve pleasure and sharing”, recalls the nutritionist. So what is good nutrition? A combination of products rich in fiber (whole grains, legumes, fruits and vegetables), raw rather than ultra-processed, fermented dairy products, animal proteins and fats in moderate quantities, no or few sugary drinks. In other words, a Mediterranean type diet. So far, scientists have found no better: large-scale studies have demonstrated its protective effects against metabolic diseases, age-related cognitive decline, and even breast cancer. “Other protocols have been developed: the Nordic diet, Dash against hypertension, the anti-inflammatory diet, or the portfolio diet against cholesterol. If you look at them closely, however, these are roughly the same recommendations, under different names”, jokes Professor Lecerf. But to hope to sell books, it is better to adorn yourself with the finery of novelty, if not to revolutionize nutrition…