Five Things Everyone Should Know About Weight Loss

The issue of weight loss is omnipresent in public debate, where it is often reduced to a question of personal willpower . But after nearly fifteen years of research in health and nutrition, I have noticed that the problem of weight is not treated in the same way as most other health issues.

People are routinely blamed for their weight, even though there is strong evidence that it results from a complex combination of genetic, biological, environmental, and socioeconomic factors.

Limited access to healthy and affordable food, a lack of opportunities to exercise, particularly due to a lack of suitable venues, long workdays and chronic stress – all more common in disadvantaged areas – can make maintaining a healthy weight significantly more difficult.

Here are five things I wish more people understood about weight loss.

1. It goes against our biology

Obesity has been recognized as a national health priority in England since the 1990s, and numerous policies have been put in place to address it. Yet obesity rates have not declined —in France, the prevalence of excess weight (including both overweight and obesity) in 2020 was 47.3%, with 17% of subjects being obese. This suggests that current approaches, which tend to emphasize individual responsibility, are not working.

Even when weight loss methods are effective, the results are often not sustainable . Studies show that most people who lose weight eventually gain it back, and the chances of an obese person reaching and maintaining a "normal" weight are very low .

This is partly because our bodies react differently when we lose weight, a biological mechanism rooted in our evolutionary past: they fight back. This process is called metabolic adaptation : when we reduce our calorie intake and lose weight, our metabolism adjusts its energy expenditure , and hunger hormones like ghrelin increase, prompting us to eat more and regain the lost weight.

This biological response made perfect sense in our hunter-gatherer past, marked by alternating periods of abundance and famine. But today, in a world where ultra-processed, high-calorie foods are cheap and accessible, these same mechanisms actually promote weight gain and prevent weight loss.

If you're having trouble losing weight or keeping it off, it's not a personal failure, but a predictable physiological response.

2. It's not a question of willpower

Some people manage to maintain their weight with relative ease, while others struggle. The difference isn't just a matter of willpower.

Body weight is determined by a multitude of factors. Genetics plays a major role, for example, by influencing how quickly we burn calories, how hungry we feel, and how full we feel after eating. Some people are genetically predisposed to feeling hungrier or craving energy-dense foods, which makes weight loss even more difficult.

Environmental and social factors also play a role. Having sufficient time and financial resources to prepare balanced meals, engage in regular physical activity, and sleep well all make a real difference. However, these resources are not accessible to everyone.

Ignoring these complex factors and viewing weight solely as a matter of willpower fuels stigma. Yet, stigma can lead people to feel judged, ashamed, or excluded, which, paradoxically, increases stress, lowers self-esteem, and makes it even harder to adopt healthy habits.

Counting calories is often the default strategy for weight loss. And while creating a calorie deficit is theoretically essential for weight loss, in practice, it's much more complicated.

For starters, nutritional information on foods is only an estimate , and our energy needs vary from day to day. Even the amount of energy we absorb from food can vary depending on how it's cooked, digested, and the composition of our gut bacteria.

There's also a persistent misconception that "a calorie is a calorie," but our bodies don't process all calories the same. A cookie and a boiled egg may contain the same number of calories, but they have very different effects on our hunger, digestion, and energy levels. A cookie may cause a rapid spike in blood sugar, followed by a sharp drop, while an egg provides a longer-lasting feeling of satiety (fullness) and higher nutritional value.

These misconceptions have contributed to the popularity of fad diets, such as protein shake diets or those that eliminate certain food groups. While they can lead to short-term weight loss by creating a calorie deficit, these diets are rarely sustainable and often lack essential nutrients.

A more realistic and balanced approach is to focus on long-term changes: eating more whole foods, cutting down on takeout, reducing alcohol consumption, and adopting habits that promote overall well-being.

4. Exercise is great for your health, but not necessarily for weight loss.

Many people believe that the more they exercise, the more weight they lose. But science shows us that the reality is more complex.

Our bodies are very good at conserving energy. After an intense workout, we may unconsciously move less for the rest of the day, or feel hungrier and eat more, which compensates for the calories burned.

In fact, research shows that total daily energy expenditure does not increase with increased physical activity. Instead, the body adapts by becoming more efficient and reducing its energy consumption elsewhere, making weight loss through exercise alone more difficult than many people think.

That said, exercise still offers a multitude of benefits : it improves cardiovascular health, mental well-being, maintains muscle mass, strengthens metabolism, strengthens bones, and reduces the risk of chronic diseases.

Even if the number on the scale doesn't go down, physical activity remains one of the most powerful tools to improve our health and quality of life.

You don't have to lose weight to be healthier.

While intentional weight loss can reduce the risk of diseases, such as heart disease and certain cancers , studies also show that eating a better diet and moving more can significantly improve health indicators, such as cholesterol, blood pressure, blood sugar, and insulin sensitivity, even if your weight stays the same.

If the scale doesn't reflect a significant change, it may be better to take a different approach. Rather than focusing on a number, you can choose a more holistic approach: a suitable diet, regular and enjoyable physical activity, attention to sleep quality, and better stress management.

Weight is just one piece of the puzzle, and health is much more than that.