Studies show that metabolism is such a complex system that it cannot be modeled with simple tricks. Knowing how it works allows you to improve strategies to avoid gaining weight or losing kilos.

Interest in fitness and body weight has led to an obsession with counting calories and controlling metabolism. Books and magazines offer all kinds of tips and advice, but they are not effective because they start from serious misunderstandings about the actual functioning of the metabolism. As a consequence, neither diet nor exercise as proposed usually serve to achieve the desired objectives.

“Diet and exercise are vitally important to our health, but they do not work in the way we are generally taught. Our bodies are a complex and dynamic metabolic system meticulously shaped by evolution for survival and reproduction,” Herman explains. Pontzer of Duke University in North Carolina in New Scientist.


It’s the fundamental belief of almost every exercise routine that appears in the magazines: exercising more means burning more calories. In the short term, that’s right: you burn energy while you exercise, and adding a new exercise routine will burn more calories. But this only happens at the beginning.

Studies show that people with very different levels of physical activity burn almost the same calories. Our bodies work to keep the daily amount of calories burned within a narrow range, regardless of our lifestyle.

When we start a new exercise routine, we certainly burn more calories but this expense is corrected as time goes by. In a few months we will be burning the same calories as before we started exercising.

Therefore, the amount of calories that are burned through exercise is not enough to lose weight in a lasting way. A recent review of 61 studies with a total of more than 900 participants shows that weight loss occurs at the beginning of a new exercise regimen, but fades over time.

In one of the longest trials, men and women burned 2,000 calories per week for 16 months. By nine months, the men had lost about 5 kg and then the weight stabilized. The women were unable to lose weight after 16 months.

The study authors explain that if we exercise more, we also get hungrier and eat more (without realizing it). As a result, the amount of weight that can be expected to lose from exercise alone over the course of a year is 2 kg or less.


The goal of exercising is not to lose weight. Biological evolution over more than 2 million years has meant that we need to exercise to stay healthy, not to lose weight. Exercise reduces inflammation, prevents heart disease and diabetes, benefits the heart, muscles, and brain, but it doesn’t help much to lose pounds.

Research indicates that metabolic adjustments that thwart weight loss are one of the main reasons exercise is so good for us. For example, exercise calms down the immune system, reducing inflammation and the intensity of allergic and autoimmune disorders.

Exercise also decreases the production of stress hormones such as cortisol and adrenaline. Even reproductive hormones are regulated: estrogen and progesterone levels are lower in physically active people, which is associated with a lower risk of prostate, ovarian and breast cancers.

Exercise seems to hone in on all the invisible tasks our bodies do throughout the day, helping us protect ourselves from heart disease, diabetes, and cancer.


The main cause of overweight and obesity is clearly diet. We gain weight because we eat too much. However, it is often said that counting calories is not the important thing. Maybe not count them, but take them into account, yes. At the end of the day, what matters is selecting healthy foods and consuming them in adequate amounts.

It is not true that if you adopt a certain diet it is not necessary to count calories. If we follow a ketogenic diet, for example, we will gain weight if we eat more calories than before.

It is true that few people know how to calculate the calories in what they eat. According to studies, men who think they eat 2,000 calories actually get 3,000. Women are wrong for less: they take 2,300.

The fact that we do not know how to count calories does not mean that they are not important, but that we have to adopt another method to control them. For example, follow the photos of recommended portions and dishes so as not to overdo the calories.

If you are trying to lose weight, the trick is to find a low calorie diet that you can maintain without suffering. Crash diets that promise weight loss in a short time and then return to our usual diet do not work because our body, in the face of scarcity, reduces daily energy expenditure. Anything that is lost is later recovered in spades.

Each person has to find the diet that helps them lose weight and that they like. In general, it is recommended that any diet be composed of natural and whole foods, without ultra-processed.


The amount of energy burned in a day varies from person to person. The daily energy expenditure of two people of the same age and sex, and with the same lifestyle, can easily differ by 500 calories or more, but that variation in energy use does not predict a person’s weight.

People with obesity have the same daily energy expenditure, on average, as thin people. Weight gain and obesity are not the result of a slow metabolism. So why do some people find it easy to stay in shape while others have a hard time?

Although there is probably no single answer to this question, the key seems to lie in the brain. Obese people suffer, so to speak, a small error in their regulation of energy intake. As a consequence, they gain weight over the years.

This error may have to do with the neural reward system that controls food intake and is overwhelmed by the abundance of attractive, caloric foods available. The brains of these people are involuntarily inclined to excess consumption.


The battle against obesity is often posed as a challenge for the individual willpower of the affected person, who must discipline himself to do physical exercise and at the same time control the portions, especially of certain foods, putting aside all gluttony. However, the science of metabolism says other things.

The problem is not so much in each individual person, but in that we are all surrounded by hyper caloric, refined and ultra- processed food products.

Recent work at the National Institutes of Health in the United States has shown that eating ultra-processed foods leads to weight gain, which accounts for up to half of the food consumed in the richest countries.

Obesity is, therefore, a largely cultural and social problem. However, each person can take individual measures. The most effective is to reject ultra-processed foods. We can’t wait for the health and political authorities to ban them.


Please enter your comment!
Please enter your name here