The lost illusion of diets

IRENE MARGARITIS Professeur de physiologie - Chef of the Unité d'évaluation des risques liés à la nutrition à l'Anses, Agence nationale de sécurité sanitaire de l'alimentation, de l'environnement et du travail (Anses)

With the arrival of sunny days, the desire to leave the sweaters and warm clothes come back. A desire that is accompanied –under social pressure– by the idea of ​​showing a body, if not perfect, at least compatible with the norm that is exhibited in magazines and where the slim figure reigns.

The purpose here is not to return to this observation, its causes and its physiological or psychological damage, supported by a large number of publications for several decades, but rather to specify the health risks of weight loss diets, induced by great physiological stress. –in turn followed or accompanied by psychological stress– and, ultimately, by weight regain in almost all cases.

Indeed, the subjective representation of body image most often presides over the choice of a diet and the objective is not necessarily consistent with maintaining the state of health: according to a French national survey, 45% of women who are not overweight, of which 15% were thin (BMI < 22), had dieted in that year. This is highlighted in a 2011 report by the French Agency for Food, Environment and Occupational Health Safety (ANSES) based on a national study on food consumption.

how the diet works

Weight loss strategies involve creating an energy imbalance by restricting the diet to release fatty acids from adipose tissue. However, rarely does everything go according to plan.

The first illusion is the initial weight loss observed, which is only linked to the use of liver and muscle glycogen (in this case our rapidly available energy reserve in the form of carbohydrates) and the elimination of water linked to it (9 grams per gram of glycogen).

In a second phase, the desired effect is produced: fat reserves are mobilized. But what is generally less well known is that our body establishes strategies to resist this weight loss.

With fewer readily available energy reserves (the ones we lost first), our body will go into economy mode (with a drop in resting metabolism): this translates into fatigue and feeling cold – thermogenesis (heat production) is reduced – which will be installed permanently if the restriction persists.

Preserve muscle mass

Another unpleasant surprise is the loss of muscle. Although the diet is qualitatively balanced, the loss of fat mass (75%) is accompanied by a loss of muscle mass (25%).

However, muscle mass is a key factor in resting energy expenditure, as it contributes significantly to thermogenesis and thus to resting energy expenditure. If there is less muscle, resting energy expenditure is de facto reduced.

To maintain long-term weight loss, it would be necessary to further reduce food intake or increase energy expenditure. This is where physical activity plays an important role, well beyond its effect on energy expenditure during exercise.

Physical activity beyond calories

Beyond the number of calories expended, the physiological effects of physical activity are at the origin of a virtuous circle: it will maintain muscle mass to a great extent. In fact, the more physically active we are, the greater the heat dissipation, even at idle. It also helps regulate blood sugar levels and hormonal and energy metabolism.

And although the hypothesis of its anorexigenic effect (appetite suppressant) is currently being explored, its role as a regulator of food intake is beginning to be well documented: by acting as a regulator of mood and stress response, it would act on feeding behavior partly under the influence of these two factors.

The practice of sport, by favoring energy expenditure and therefore caloric balance, maintaining muscle mass, helps control weight in the long term. /

Jacek Chabraszewski/Shutterstock

Health risks of diets

In 2011, for the first time in the history of health risk assessment in this field, 15 diets were studied by ANSES. They all had common consequences: energy restriction by controlling food intake and eliminating at least one food category leads to deficiencies in certain minerals, vitamins, fibers or excesses in protein, sodium, psychobehavioral, biological, pathophysiological, muscle mass, hormonal balance, bone status, kidney and liver functions.

All restrictive diets, by their very purpose, lead to nutritional imbalances.

In addition, there is a paradox: the sometimes spectacular short-term effect of these diets masks the main health risk, the almost systematic regain of weight, which is observed in 80% of cases one year after the diet and in 95% of cases in five years. This observation makes it a public health issue that remains relevant in 2022.

It is without a doubt because the slimming diet is lived as a transitory measure. It becomes a parenthesis, despite the fact that it could be the path towards a dietary behavior that supports the return to nutritional balance or even that aims to improve metabolic, cardiovascular and psychological parameters.

However, the limitations generate psychological and physiological stress that few are able to withstand in the long term. It is in this context where physical activity and a reasoned nutritional approach acquire all their importance. They are necessary for long-term health maintenance and the prevention of sudden weight gain.

Understand the origin to give support

When being overweight is real, its origin can be found in dietary errors, lifestyle, stress, physical inactivity, age, metabolic or hormonal disorders, etc. As soon as triggering or maintenance factors are not identified, the fight against excess weight begins.

Therefore, diagnosis and individualized follow-up by a health professional –nutritionist, dietitian– are essential to understand the origin and control the health consequences of nutritional imbalances.

A restrictive diet cannot fit thousands of people. If the initiative is individual, the support must also be individualized. Dietary practices, lifestyle adequacy and personal history are crucial points to support the demand for weight loss which, to be truly satisfied, must have long-term mental and physical health as its primary goal.

Under normal circumstances, when energy reserves are depleted, the brain responds by emitting hunger signals. The restriction and control of food intake then come into conflict with physiological needs: permanent control will end up permanently disturbing the emission and interpretation of the signals of hunger and satiety that regulate eating behavior.

The harmony between nutritional needs and food intake is permanently and in some cases permanently disrupted. This alteration is at the origin of eating disorders and at the origin of weight gain after dieting, already documented for several decades.

If restrictive diets are carried out without having previously identified the causes of overweight, the loss of kilos will be followed by their recovery. With the restriction-induced decrease in energy metabolism, eating will then lead to weight gain beyond the initial weight, which in turn leads to repeat dieting.

This phenomenon is at the origin of the yo-yo effect, which increases after each episode. These restrictive diets that are sold to lose weight are at the very origin of weight gain. So to prevent it from happening, a very good solution is physical activity, which will act as a regulator in many aspects through the well-documented physiological and psychological role it can play.

This article has been published in '
The conversation'.

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