Every year, new diets appear, promising to solve all my weight and health problems. The global weight loss diet market is estimated at more than $200 billion. However, scientific studies provide a nuanced, sometimes surprising assessment: the vast majority of restrictive diets fail in the long term, and some can even harm your health. Taking stock of what the research really says about the main diets is essential to navigating this nutritional jungle with lucidity.
1. Why most diets fail in the long term
Before analyzing specific diets, it is essential to understand why, in general, they do not work sustainably. The data is edifying:
- ●A meta-analysis published in The American Psychologist (2007) covering 31 studies concluded that low-calorie diets allow short-term weight loss, but that 1 to 2/3 of people who followed a diet regain more weight than they had lost in the following 4 to 5 years.
- ●The rebound phenomenon (yo-yo effect) is documented: severe caloric restriction triggers biological adaptation mechanisms - slowing down of basic metabolism, increase in ghrellin (hunger hormone), reduction in leptin (satiety hormone) - which make weight regain almost inevitable.
- ●Cognitive restriction, that is to say the constant monitoring of one's diet, is associated with an increased risk of eating disorders and food anxiety.
This reality does not mean that it is impossible to lose weight or improve your health through diet. It means that the approach makes all the difference: lasting changes in eating habits consistently outperform temporary restrictive diets in long-term studies.
| Diet | Principle | Evidence of effectiveness | Risks and limitations |
|---|---|---|---|
| Mediterranean diet | Rich in vegetables, fish, olive oil and legumes. Red meat limited. | The best documented scientifically. A 30% reduction in cardiovascular risk (PREDIMED study, NEJM 2013). Protection against type 2 diabetes, some cancers and depression. | No identified risk. Harder to sustain outside a Mediterranean food culture. |
| Ketogenic diet | Very low in carbohydrates (under 50 g a day), high in fat. Induces metabolic ketosis. | Effective in the short term for weight loss and blood sugar control in type 2 diabetes. Established benefits in drug-resistant epilepsy. | Hard to sustain. Risk of fibre and micronutrient deficiencies. Impact on the microbiota. Contraindicated in kidney or liver disease. |
| Intermittent fasting (16:8, 5:2) | Alternating periods of eating and fasting. The 16:8 pattern limits the eating window to 8 hours. | Effective for weight loss and insulin sensitivity in the short term. Results comparable to continuous calorie restriction according to the NEJM (2019). | May encourage compulsive eating behaviour in predisposed individuals. Not advised for pregnant women, elite athletes or people with diabetes on treatment. |
| DASH diet | Rich in fruit, vegetables, low-fat dairy and wholegrains. Low in salt and saturated fat. | High level of evidence for lowering blood pressure. Recommended by the WHO and cardiology societies. | Few risks. Requires disciplined meal organisation. |
| Gluten-free diet | Complete elimination of gluten (wheat, barley, rye). | Essential in coeliac disease and confirmed sensitivities. No proven benefit in non-coeliac individuals according to a Cochrane review (2017). | Risk of fibre, iron and B vitamin deficiencies. Industrial gluten-free products are often higher in sugar and less nutritious. |
| Detoxes and juices | Periods of consuming only fruit and vegetable juices. | No scientific evidence of a detoxifying effect. The liver and kidneys perform this function continuously. | No protein intake, risk of deficiencies, muscle loss. Can foster an unhealthy relationship with food. |
3. The Mediterranean diet: the only one with a strong scientific consensus
Among all the diets studied, the Mediterranean diet is by far the one that benefits from the highest level of evidence and the broadest scientific consensus. The famous PREDIMED study, published in the New England Journal of Medicine in 2013 and involving more than 7,000 participants, showed a 30% reduction in major cardiovascular events in the group following a Mediterranean diet supplemented with olive oil or nuts, compared to the control group on a low-fat diet.
What sets the Mediterranean diet apart from others:
- ●It is not a restrictive diet: it does not prohibit anything, it hierarchizes. The emphasis is on abundance of beneficial foods rather than cutting out harmful foods.
- ●It is holistic: it includes cultural and social dimensions - eating together, taking meal time - which independently contribute to well-being.
- ●It is sustainable: unlike restrictive diets, it can be maintained indefinitely without feeling deprivation.
- ●Its benefits are multiple: cardiovascular protection, reduction in the risk of T2 diabetes, cognitive protection, reduction of systemic inflammation, benefits on the intestinal microbiota.
4. What all effective diets have in common
Beyond their differences, a cross-sectional analysis of diets that show positive long-term results revealed several common points:
- ●They favor unprocessed or minimally processed foods: whatever the diet - ketogenic, Mediterranean, DASH, vegetarian - whole and minimally processed foods are favored.
- ●They reduce ultra-processed foods: the reduction of ultra-processed products is the common denominator of all dietary approaches beneficial to health, regardless of macronutrition.
- ●They increase the consumption of plants: more fruits, vegetables, legumes and whole grains is a recommendation that cuts across all effective approaches.
- ●They are part of an overall lifestyle change: studies show that diets work better when they are accompanied by regular physical activity, better quality of sleep and stress management.
5. The weight question: what science really says
The relationship between diet, weight and health is more complex than the simple calculation of calories in / calories out. Some scientifically established points to remember:
- ●Body weight is influenced by genetic (estimated at 40-70% according to twin studies), hormonal, microbiomic and psychological factors, not just diet.
- ●Body mass index (BMI) is an imperfect indicator of metabolic health: you can have a normal BMI with a poor metabolic profile, and vice versa.
- ●Metabolic health - fasting blood sugar, blood pressure, triglycerides, HDL-cholesterol, waist circumference - is a more relevant indicator than weight alone for assessing cardiovascular and metabolic risk.
- ●Several studies, including one published in JAMA (2005), show that slightly overweight people (BMI 25-30) have all-cause mortality comparable to, or even lower than, people of normal weight. Diet quality and physical activity level are more robust predictors of health than weight.
💡 tips to remember
- Most restrictive diets fail in the long term: 2/3 of people regain more weight than they lost within 5 years. The problem is not me, it's the approach.
- The Mediterranean diet is the only one with a strong scientific consensus: reduction of cardiovascular risk by 30%, protection against diabetes, depression and cognitive decline. And it doesn't prohibit anything.
- All effective diets have one thing in common: they favor unprocessed foods and reduce ultra-processed foods, regardless of their macronutrition.
- Detox cures have no scientific basis: my liver and my kidneys ensure permanent detoxification without the need for juice.
- Weight is not not the only indicator of health: blood sugar, blood pressure, triglycerides and waist circumference are more relevant markers of metabolic risk. It is not suitable for all profiles.
- The best approach is the one that I can maintain indefinitely with pleasure: lasting changes in habits always outperform temporary diets.
