For decades, we’ve been told that losing weight is just a matter of willpower: eat less and move more. But modern science has proven that this is not the case. This will be discussed later. But first, let’s go back a few hundred thousand years to look at our early human ancestors. Because much of the difficulties we face today in losing weight can be attributed to them – perhaps the greatest example of “blame the parents.”
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For our ancestors, body fat was a matter of survival: too little could mean starvation, too much could leave them inactive. Over time, the human body has become very effective at protecting its energy reserves through complex biological defences, commanded by the brain. But in a world where food is plentiful and movement is optional, these same systems that once helped us survive now make it difficult to lose weight.
When someone loses weight, the body reacts as if it poses a threat to survival. Hunger hormones increase, food cravings increase, and energy expenditure decreases. These adaptations have evolved to improve energy storage and use in environments where access to food is diverse. But today, with easy access to cheap, high-calorie, highly processed foods, coupled with a sedentary lifestyle, these same adaptations that once protected us are now working against us.
As we have pointed out in recent research, the brain also has powerful mechanisms to defend body weight and can, to some extent, “remember” how much it weighed previously. For our ancestors, this meant that if they lost weight during difficult times, their bodies would be able to “return” to their usual weight in better times.
But for us modern humans, this means that our brains and bodies remember excess weight as if our survival depended on it. In practical terms, once a body becomes heavier, the brain treats this higher weight as the new normal, a level it feels compelled to defend.
The fact that the body has this ability to “remember” its previous weight helps explain why so many people regain the weight they lost after dieting. As science shows, this weight regain is not a lack of discipline, it is simply the body doing what it evolved to do: defending itself against weight loss.
This is where weight loss drugs like Wegovy and Mounjaro offer new hope. They work by mimicking gut hormones that tell your brain to control your appetite.
But not everyone responds well to these medications. For some, side effects may make it difficult to adhere to treatment, and for others, medications do not seem to lead to weight loss. It is also common that after stopping treatment, the body begins to move again and the lost weight returns.
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Advances in research into obesity and metabolism may mean that treatments may in the future be able to suppress these signals that cause the body to return to its original weight, even after a period of treatment.
Research also shows that good health is not the same as a “healthy weight.” In other words, physical exercise, good sleep, a balanced diet and mental health can improve cardiovascular and metabolic health, even if the number on the scale practically does not change.
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A whole-of-society approach
Of course, obesity is not just an individual problem – addressing it effectively requires a collective approach. Research suggests that several preventative measures can make a difference: investing in healthy school meals, limiting fast food advertising to children, designing neighborhoods that prioritize walking and cycling over cars, and standardizing portion sizes served in restaurants.
Scientists are also interested in critical stages early in life, from pregnancy until about age seven, when a child’s weight regulation system is particularly flexible.
In fact, studies show that factors such as parental nutrition, the way a child feeds and lifestyle habits in childhood can shape the way the brain controls appetite and fat storage for many years.
If you want to lose weight, there’s still a lot of work to do, especially by focusing less on crash diets and more on sustainable habits that support overall health. Prioritizing sleep helps regulate your appetite, for example, while regular physical activity, even simple walking, improves blood sugar levels and cardiovascular health.
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In short, obesity is not a personal failure, but rather a biological condition shaped by our brains, our genes, and the environments in which we live. The good news is that advances in neuroscience and pharmacology provide new opportunities for treatment, while prevention strategies could change the landscape for generations to come.
So, if you’re having trouble losing weight and keeping it off, know that you’re not alone and it’s not your fault. The brain is a formidable opponent. But with smarter science, medicine and politics, we are beginning to change the rules of the game.
* Waldemar Bremnes Engemann Johansen is a PhD fellow at the Faculty of Health Sciences and Medicine at the University of Copenhagen, Denmark.
* Christopher Clemmensen is Associate Professor and Group Leader at the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen, Denmark.
*This article is republished from The Conversation under a Creative Commons license. Read the original text.
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