It has become known why the brain resists maintaining lost weight

For decades, people have been told that losing weight is a matter of willpower: eat less, move more. However, modern science shows that this is not the case, researchers explained.

This was reported by The Conversation portal.

For ancient human ancestors, fat reserves were key to survival: too little fat threatened starvation, too much slowed them down. Over thousands of years, the body learned to reliably protect its energy reserves through complex biological mechanisms hardwired into the brain. The problem is that in the modern world, with an abundance of food and minimal movement, the very same systems that once helped with survival now hinder weight loss.

When a person loses weight, the body reacts as if it were a threat to survival: hunger hormone production increases, food cravings intensify, and energy expenditure decreases. The brain has powerful mechanisms for defending body weight — it is capable of "remembering" the weight a person previously had and strives to return precisely to that level.

For ancient ancestors, this meant that after times of hunger, the body could restore its usual weight during a more prosperous period. But in modern humans, the same mechanism means that the brain perceives any excess weight gained as a new norm that needs to be defended. This is precisely why so many people regain weight after dieting — and it is not about a lack of discipline, but rather that biology is working exactly as evolution intended.

Hope comes from weight-loss medications such as semaglutide and tirzepatide: they mimic gut hormones that signal the brain to reduce appetite. However, they are not suitable for everyone — in some people the medications cause side effects, while in others they do not lead to weight loss at all; after discontinuing treatment, biology often takes its course, and the weight returns.

Researchers emphasize that good health is not the same as having the "right" weight: sleep, nutrition, and physical activity improve heart function and metabolism, even if the number on the scale barely changes. Scientists pay particular attention to the early period of life — from pregnancy to approximately age seven — when a child's weight regulation system is especially malleable and is shaped by the parents' diet.