PROFESSIONAL ARTICLE

The metabolic set point theory
By: Dr. Joana Menezes - Endocrinology

We all know someone who lost weight and regained it, or even gained more. And we all hear the same old clichés: “they didn't have the willpower,” “look at the state they got into,” or worse, “it was my fault,” “I lost control and ended up back where I started.”

NO! It is time to change the narrative and remove this stigma from people living with obesity. Because NO! It is NOT their fault, nor is it a lack of willpower or laziness. It is a NORMAL biological, metabolic response, as normal as sweating in a sauna, shivering from the cold in icy water, or not being able to focus when you have ADHD. But how?

When it comes to weight, the human body behaves like a thermostat. It does not defend an exact number, down to the decimal, but rather a weight range, and it works actively to stay within it. This is what is called the metabolic set point, or defended weight. When we drop below that range, the body does not remain indifferent: it reacts (just as it reacts to sweat inside a sauna). And it reacts in a very specific way. Energy expenditure decreases more than would be expected by the mass that was lost - the body starts to function on less fuel than someone of the same size who had never lost weight would have to burn (a decrease in basal metabolic rate). At the same time, the hormones that regulate appetite change their stance: leptin, which signals satiety, drops; ghrelin, which triggers hunger, rises. The result is feeling hungrier, experiencing more cravings, and burning less energy (even if you maintain muscle mass and healthy lifestyle habits).

The best-known study followed contestants from a weight loss television show (The Biggest Loser) for six years. Most regained the weight, but the lasting takeaway was different: their metabolism remained reduced years later, even in those who had returned to their starting point. The body maintained its defense long after the diet had ended.

Seen in this light, regaining weight is no longer a moral failure and becomes what it actually is: a predictable biological response.
This does not absolve anyone of responsibility, but it changes the question, the paradigm, and the stigma. The issue is not why the person failed to keep the weight off. It is why we expect anyone to defeat, through willpower and indefinitely, a system that evolution has fine-tuned over millennia to protect us against scarcity - yes, this is a biological inheritance from our ancestors; it is an adaptive, evolutionary advantage.

This leads to the next question: can the defended set point change? The answer seems to be yes, although it is slow and we do not know the timeframes or time limits. Treatments that act on the actual hormonal pathways of appetite regulation - metabolic surgery and the latest medications - do not just make you lose weight; they fight against the biological response of increased hunger and cravings and seem to lower the threshold that the body defends. This is also why, when treatment is suspended, the weight tends to return. It is not the medication that fails; it is the defended set point returning to what it was. It makes more sense to think of this like blood pressure than like an antibiotic.

It is fair to say that the theory is not consensual in its most rigid form. There are researchers who advocate for more flexible models, in which the environment, the availability of food, and habits shift this point over the course of a lifetime. But the core is accepted: there is an active biological regulation, and it does not turn off by choice.

In practice, here is what we should all take away: NO, it is not your fault; your body is NOT against you - it is doing what it was built to do.

The 5 pillars of lifestyle medicine: healthy eating, regular physical activity, sleep health, good stress management, avoidance of substances harmful to health.

Demystifying healthy eating: no, the culprit is not potato soup or breakfast bread. A healthy diet, nowadays, is the Mediterranean diet; in very simple terms, our traditional “food wheel” from primary school. The issue lies in the combination and quantities. Prioritize micronutrients (vitamins and minerals found, for example, in vegetables and fruits) and eat macronutrients (slow-release carbohydrates, proteins, and fats—ideally the healthy ones) in appropriate proportions.

It should be noted that for people in the process of losing weight, protein intake should be increased so as not to compromise muscle mass.

And without a doubt, never skip follow-ups, even if it is just annually, with your doctor, because the problem is not losing the weight, but rather keeping the lost weight off.