"I exercise, so why am I not losing weight?"

I see people who run, cycle, go to the gym three or four times a week. Some even take part in endurance races. And yet, some of them remain overweight or carry a significant amount of abdominal fat.

So they say to me: 'Doctor, I don't understand. I exercise a huge amount and I'm not losing weight.' And my answer is usually the same: because exercising and losing fat are two different things.

Exercise is probably one of the best medicines we have for our health. But its value absolutely cannot be reduced to the calories it burns. And above all: you cannot ask your training to indefinitely compensate for what you eat and drink.

1. To lose fat, you need to create an energy deficit

Let's start with the most fundamental physiology. Our body obeys the laws of thermodynamics. To sustainably lose energy reserves — particularly fat — the body must ultimately expend more energy than it receives. This is what we call an energy deficit.

Exercise can contribute to this deficit. But contributing does not necessarily mean creating it.

Let's take a deliberately simplified example. You complete a training session and burn a few hundred extra kilocalories. Very good. But after your session, you have a sugary energy drink, an energy bar, a high-calorie protein bar, a smoothie, or simply a much larger meal because you feel you have 'earned' the right to eat more.

You can very quickly recover a large portion of the energy you have just expended. Sometimes even more. And your deficit disappears.

2. We massively overestimate how much we burn

This is probably one of the most common mistakes. After 45 minutes of exercise, we sometimes have the impression of having achieved an enormous energy expenditure. Physiologically, for the average person, that is generally not the case.

A professional athlete capable of sustaining an extremely high output for several hours is obviously a different situation. But that is not the reality for the majority of the population.

For someone doing a standard gym session, cycling, running, or cardiovascular training, the additional expenditure remains relatively limited compared to how easily we can consume energy.

And this is where our modern food environment becomes formidable. It is far easier to eat 500 calories than to burn 500. A few minutes can be enough to consume them; burning them can require a long period of physical activity.

3. The trap of 'sports' drinks

This is something I see regularly. A person completes a fairly moderate session… and during or after training, they drink an energy drink containing carbohydrates. Why? Because they are doing sport.

For certain prolonged training sessions or specific sporting situations, carbohydrate intake during exercise can be genuinely justified. But for someone whose primary goal is to lose body fat and who is completing a relatively short or moderate session, this deserves to be individualized.

If you are expending energy during your workout only to immediately reintroduce a significant amount in liquid form, you are simply reducing or cancelling out part of the deficit you were trying to create. And liquid calories have a particular characteristic: they are extremely easy to consume.

4. "I can eat that — I worked out"

Here is another trap. Sport sometimes gives us a kind of psychological permission. "I went for a run this morning," so I can have dessert. "I went to the gym," so I can have that bar. "I cycled for an hour," so I can eat more tonight.

The problem is that our brain does not necessarily calculate both sides of the equation correctly. We can overestimate the calories burned and underestimate those we consume. A workout then unconsciously becomes a justification for eating more. And the energy deficit we thought we had created no longer exists.

5. Even more interesting: energy compensation

Our body is not a simple calculator. Imagine: "I burn an extra 400 calories by exercising, so my total daily energy expenditure automatically increases by 400 calories." In reality, it can be more complicated than that.

The body has various adaptive mechanisms. After a training session, some people will, for example, move less spontaneously for the rest of the day. They will sit more. They will be more tired. They will walk less. Their NEAT — that is, all the spontaneous physical activity that is not sport — can decrease.

There are also physiological mechanisms that adapt energy expenditure. This means that the increase in total daily expenditure is not necessarily exactly equal to the calories theoretically burned during training. Our body can compensate for part of it, and this compensation varies enormously from one person to another.

This is, incidentally, the idea behind the so-called constrained total energy expenditure model: total expenditure does not always rise in a strictly additive way with each calorie spent in activity. This hypothesis remains debated, but it was the subject of a new scientific review in 2026.

6. And what about appetite?

Here again, things are interesting. Exercise can have complex effects on hunger and satiety. An acute session can even temporarily reduce the sensation of hunger in some people.

But over the long term, the body also seeks to maintain its energy balance. Some people will therefore spontaneously increase their food intake. Not necessarily by a great deal, but enough to offset part of the deficit created by exercise. And a few hundred extra calories each day can completely change the outcome over several months.

7. This is why you can be athletic and still carry abdominal fat

This is perfectly possible. Being physically active does not automatically mean being in an energy deficit. You can run several times a week and consume enough energy to maintain your weight. You can cycle every weekend and consume more than you expend. You can have an excellent cardiorespiratory capacity and still carry a significant amount of body fat.

You can even develop good athletic performance while remaining overweight. Athletic performance and body composition are not the same thing. And conversely, being slim absolutely does not mean being in good physical condition.

A word of caution, however: the overweight athlete is not scientific 'proof' — they simply illustrate the principle that a high level of physical activity does not necessarily imply a low body fat mass. The ACSM now emphasises the role of exercise in weight management, preservation of lean mass, metabolic health, and long-term maintenance, rather than viewing it merely as a machine for shedding kilograms.

8. So what is the point of exercise, if it is not primarily about losing weight?

This is where I want to completely change the way you think about exercise. Do not exercise simply to burn calories: that would be reducing it to one of its least interesting effects.

Exercise to improve your cardiovascular system, to increase your cardiorespiratory capacity, to preserve and develop your muscle mass, to improve your insulin sensitivity, to improve your endothelial function, to stimulate mitochondrial adaptations, to maintain your functional capacities, to protect your bones, to preserve your independence as you age, to improve your metabolic health, and to contribute to your longevity.

That is why I want you to exercise. Not simply because a treadmill tells you that you have 'burned 327 calories'.

9. Muscle also changes the equation

When you lose weight solely by reducing your food intake, you also risk losing part of your lean mass. This is precisely where exercise — and resistance training in particular — becomes fundamental.

The goal is not simply to lose weight. The goal is more accurately to lose fat while preserving as much muscle as possible. Because your muscle mass contributes to your metabolic health, your insulin sensitivity, your functional capacity, and your future independence.

Two people can therefore lose exactly five kilograms with very different effects on their body composition. Body composition matters far more than the simple number displayed on the scale.

10. So, does that mean you have to stop exercising in order to lose weight?

Obviously not. That would be exactly the opposite of the message I want to convey. Exercise is part of an overall strategy for managing overweight and obesity. It helps improve body composition, it contributes to preserving lean mass, it dramatically improves a great many metabolic parameters, and it becomes particularly important for maintaining weight loss over the long term.

But we must assign it the right role. Diet more readily creates the energy deficit. Exercise helps build and preserve a metabolically healthier body. And the two work together.

11. Don't automatically 'eat back' your workout

This is probably my most practical piece of advice. After your session, don't automatically think: 'Now I've earned the right to eat more.' First, ask yourself what your goal was.

If you are an endurance athlete training for several hours at a time, your nutritional needs are specific. If you are preparing for a competition, the situation is different again. But if you are overweight, your goal is to lose fat, and you have just completed 40 minutes of moderate activity, you do not necessarily need a sugary drink, an energy bar, and a food reward in order to 'recover.'

Stay hydrated. Eat normally. Consume enough protein. Favour minimally processed, filling foods. And adjust your intake to reflect your true level of activity.

If I had to sum all of this up in a single sentence: don't try to run off the calories you eat — eat well to lose fat, and train your body to build health.