For a long time, it was believed that losing weight was a matter of willpower: one simply had to eat less and move more. However, an international team of scientists has discovered that things are much more complicated. The human brain actively resists weight loss, perceiving it as a threat to survival. The respective study was published in the journal Cell.

For our ancestors, fat was a vitally important energy reserve. If there was too little of it, one could die of hunger; if there was too much, mobility would decrease and the ability to resist external threats would weaken.

Over hundreds of thousands of years of evolution, the human body has developed powerful biological mechanisms to protect stored reserves. But in a world where food is available at any moment and movement has become an optional activity, those same systems now prevent weight reduction.

When a person starts losing weight, the body responds as if it were under threat: hunger increases, appetite hormones rise, and metabolism slows down. The body tries to conserve energy — a behavior that once ensured survival, but now hinders weight loss.

The brain remembers the higher weight and strives to maintain it even if a person has slimmed down. This explains why it is difficult for many people to keep the results after dieting — the body simply returns the weight to its previous level, considering it safe.

“Weight gain activates brain systems that perceive this level as normal. After weight reduction, the body tries with all its might to return to it — this is not weakness, but biology, honed by millions of years of evolution,” the study’s authors noted.

Modern weight-loss drugs work by mimicking intestinal hormones that signal the brain about satiety. They help bypass the body’s natural weight-preserving mechanisms, but their effect is not universal. Some patients face side effects, or fail to achieve the expected results. After stopping the therapy, the weight often returns.

“If you find it difficult to lose weight and maintain the result, know this: you are not alone — and it's not your fault. Your brain is simply doing what it has always done — protecting you,” the researchers concluded.

They believe that further advances in neurobiology and metabolism research will help develop methods capable of “reprogramming” the brain’s signals and stabilizing weight even after the weight-loss process is over.