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Updated on 05/08/2016

Weight-loss diets

Risks related to dietary weight-loss practices

Keywords : Nutrition, Weight-loss diets

Overweight and obesity are major public health problems among adults in France. Affected individuals may need to follow set diets as part of medical care provided by healthcare professionals. However, these weight-loss diets are often followed by people who are not overweight or without a medical justification, primarily for aesthetic reasons. ANSES received a formal request from the health authorities to carry out an assessment of the health risks related to dietary weight-loss practices.

Overweight and obesity are major public health problems, affecting respectively 32% and 15% of people over 18 years of age in France. These diseases, which are real public health issues, need to be managed by a healthcare professional and may warrant a weight-loss diet with medical follow-up. However, in many cases, dietary weight-loss practices are adopted by individuals who are not overweight or without medical justification, primarily for aesthetic reasons.

As part of the National Health and Nutrition Programme (PNNS) and its subsequent updates, ANSES received a formal request from the Ministry of Health to assess the risks related to weight-loss practices, in the context of the wider issue of “body image”.

The focus was to provide the health authorities with objective indicators to better identify the potential harmful consequences of weight-loss diets when they are followed without being recommended or monitored by a specialist, with the aim of assisting the health authorities in proposing prevention policies as part of the future PNNS 3 programme. 


Expert appraisal process

Further to a collective expert appraisal procedure, a report was issued by a working group comprising scientists and experts in nutrition. It was validated by the ANSES Expert Committee (CES) on Human nutrition, and published in November 2010. 

Several hearings were conducted during the drafting process of this report, but given the importance, complexity and sensitivity of the subject, ANSES felt that further consultation was needed. Interested stakeholders including members of the scientific and medical community, representatives of associations, and leaders of professional organisations were therefore informed of the expert appraisal. The subject was opened to consultation for a period ending on 15 January 2011. 

The contributions received and the clarifications (lien sur le texte à revoir) provided by ANSES were made public. This information was analysed and resulted in an ANSES Opinion presenting recommendations and final conclusions, which was validated by the Expert Committee (CES) on Human nutrition and published in May 2011.

The weight-loss diets studied by ANSES were chosen based on their popularity, i.e. those that are cited most frequently on the internet or those that are dealt with in best-selling press or internet publications. Fifteen different diets were selected in this way (1).

The diets in question differ in terms of nutritient composition. Depending on the case, they recommend removal of one or several categories of food, consumption of only one category of food, or even total removal of  some foods.

The expert appraisal carried out by ANSES focused on two areas:

  • identification and characterisation of weight-loss diets to determine their impact on nutritient intake, specifically in terms of inadequate nutrition;
  • analysis of available literature data to identify:
    • the biological consequences of weight-loss diets; this analysis included identification of nutritional imbalances in macronutrients, and insufficient intake of vitamins and minerals;
    • the pathophysiological and psycho-behavioural consequences of weight-loss diets.

Specific assessments were also conducted for certain population groups with specific physiological characteristics or particular susceptibility, such as children, adolescents, pregnant and breast-feeding women, the elderly, and athletes or individuals engaged in physical activities.


Risks identified

Some weight-loss diets may result in nutritional imbalances, specifically: excess protein and salt intake, insufficient intake of fibre, iron, magnesium and vitamin D. 

These imbalances can lead to health problems:

  • depression and loss of self-esteem are common psychological consequences of repeated failures of dieting; 
  • weight loss does not only involve loss of body fat alone, but rapidly leads to loss of muscle and bone mass, regardless of the level of protein intake;
  • some diets that involve consumption almost exclusively of meat, fish, eggs, and dairy products result in very high protein intakes (hypocaloric-hyperprotein diets), and may be harmful to the kidneys, bone and heart;
  • one of the major recurring effects of food deprivation and exclusion, irrespective of the diet, is paradoxically weight regain, or even overweight: the more an individual diets, the greater the propensity for weight regain, leading to a yo-yo effect, particularly if the person is not physically active.
  • energy restrictions during pregnancy and the corresponding nutritional deficiencies involve risks for the course of pregnancy, slow foetal development and growth, and may have an impact on the child’s health later on, even in adulthood;
  • in children and adolescents, calorie restriction, whether or not associated with protein restrictions, can result in slower pubertal growth and development.
  • All changes in diet that aim to introduce an energy imbalance for the purpose of weight loss, with or without an imbalance in intake of macronutrients (carbohydrates, fats, proteins), may involve serious health risks. As such, all weight-loss diets, whether they have a specific name or not, should be avoided, unless they are monitored by a healthcare professional.

It is important to note that physical activity is an essential factor in stabilising weight. 


Conclusions and recommendations 

The ANSES appraisal demonstrated that weight-loss diets involve risks for health of varying degrees of severity. 

Attempts to lose weight by dieting are only justified if motivated by health reasons and these practices must only be followed under specialist medical monitoring by a nutritionist or dietician, medical practitioners who are able to determine which diet is best suited to the specific characteristics of each patient. 

ANSES also draws attention to the fact that in terms of health, nothing can replace a balanced, varied diet ensuring that the daily energy intake does not exceed requirements. Moreover, to reduce the risks of weight gain, changes in eating habits should be accompanied by regular physical activity.

(1)The Atkins Diet, the Sonoma Diet (Dr Guttersen), the Lemon Detox Diet, the Chrononutrition Diet (Dr Delabos), the 1st Personal Diet (Dr Cohen), the Dukan Diet, the High Speed Diet (Dr Fricker), the Mayo Clinic Diet, the South Beach Diet (Dr Agatston), the Montignac Diet, the Ornish Diet, the Scarsdale Diet (Dr Tarnower), the Cabbage Soup Diet, the WeightWatchers Diet, the Zone Diet (Dr Sears).