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French Agency for Food, Environmental and Occupational Health & Safety

Weight-loss diets are not without risk

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News of 08/06/2012

8 June 2012

For many people the arrival of summer is traditionally synonymous with the pursuit of slimness, and during this period a variety of regimes are promoted in the media. At the end of 2010, ANSES published an expert assessment emphasising the fact that weight-loss diets followed without the recommendation or supervision of a specialist could be a source of health risks. Here is an update on the issue with Irène Margaritis, head of the Nutritional risk assessment unit at ANSES.

Overweight and obesity are on the rise throughout the world. Why study the risks of dieting?
Overweight and obesity are real public health problems that require treatment by a healthcare professional and for which dieting may be warranted. But we are faced with a paradox. An increasing number of people attempt to lose weight on their own without any medical indications, essentially for aesthetic reasons. The Internet has made it especially easy to gain direct access to a variety of diets, and this encourages certain people to undertake dieting alone.
The INCA 2 (1) study showed that over 30% of "normal-weight" women surveyed and 15% of "thin" women were either on a diet at the time of the survey or had been on a diet in the year preceding the survey. Recently, the Nutrinet study showed that close to two out of three normal-weight women dieted and 27% of normal-weight men expressed their desire to lose weight. This pursuit of slimness and the proliferation of diets that can be followed alone, without medical supervision, have prompted the authorities to question the risks related to these practices.

What is ANSES's work on the topic all about?
Our assessment work examined the impact of diets in general. Basically, we sought to identify the diets that are the most widely available to the public, both through traditional marketing and on the Internet. Fifteen diets were selected based on their popularity. We wanted to ascertain whether following these diets required adopting a nutritionally imbalanced regimen.
We calculated the nutritional intake for each of them, and based on our findings we analysed the available scientific data to determine their biological impact, in terms of nutritional imbalances or insufficient vitamin or mineral intakes. We also examined whether these diets might have any pathological psycho-behavioural effects.

The main conclusion of your 2010 report was that following weight-loss diets exposes people to certain risks. Can you discuss this point further?
Our primary conclusion is that choosing to restrict ones diet, in some cases drastically, in order to lose weight is not a trivial act. The expert assessment that we conducted provided scientific proof of this. Our work revealed a number of harmful effects for the bones, heart and kidneys in particular, as well as psychological disturbances, including severe behavioural eating disorders (anorexia, bulimia, etc.). And when losing weight, muscle is also lost. Since muscle produces heat, this means that less heat is produced by the body when dieting, so more calories are stored... An analysis of the scientific data also showed that dieting can cause profound changes in energy metabolism. These modifications are often the starting point of a vicious cycle of weight regain, which may even be exacerbated in the medium or long term. It's what is commonly called the "yo-yo effect".
So, regardless of the diet selected, one of the principal recurrent consequences of the restrictions and exclusions of dieting is paradoxically that the weight is often regained, and the dieter may even become overweight. The more diets you go on, the higher the chances of gaining back the weight you initially lost.

Does that mean that one should never diet at all?
Certain situations (obesity, overweight, severe weight gain) may require making the effort to lose weight. But in all cases, it is necessary to make a precise diagnosis of the causes of the weight gain. A weight-loss plan must be undertaken with the help of a health professional who can analyse the context of the weight gain and its repercussions. Only with this support is it possible to determine whether weight loss is necessary or not and to set goals and the means of implementing them in order to succeed. A cautious and well-adapted weight-loss plan should be devised in advance (in order to deal with the factors at the origin of excess weight) and followed by a stabilisation period based on appropriate methods which strives to preserve the physical and psychological health of the individual in both the medium and long term.

What would you recommend to people who want to lose weight?
When excess weight is not an issue, weight-loss diets pose a risk to health. Therefore, in situations where weight loss is not medically warranted, dieting is not recommended, especially when it involves eating a poorly-balanced diet or one that lacks variety.
It's quite simple, when it comes to health, nothing can replace eating a well-balanced diet which includes a variety of different foods. The key to not gaining or regaining weight is to monitor daily caloric intake to ensure the energy consumed does not exceed individual requirements. In other words, avoid eating if you're not hungry, and when eating a meal, be sure to stop as soon as you feel full. In order to do this, you need to be aware of your body's hunger and satiety signals. And finally, to reduce the risks of gaining weight, it is important to not only monitor your eating habits, but also to make sure you get sufficient exercise by walking or biking more, reducing periods of inactivity, and if you are not yet doing so, participating in physical activities that are pleasurable so that they will become a regular part of your lifestyle.

(1) The INCA (French Individual Survey on Food Consumption) studies are national surveys carried out by ANSES every six years. They involve recording the eating habits of a sample group of people living in metropolitan France for a period of seven days; the second INCA study was conducted in 2006-2007.

Find out more

> Our close-up
> The Opinion dated 4 May 2011 "Opinion of ANSES concerning the request to evaluate the risks related to dietary weight-loss practices"
> The report entitled "Report on the evaluation of the risks related to dietary weight-loss practices" (in French only)