Scientists believe they have discovered what causes the middle-aged spread, and, more importantly, how to stop it.
Researchers found that signals in the brain which tell us to stop eating when full become less efficient with age.
Although it may only mean we eat a few more forkfuls of food, the extra calories soon add up to about 1lb of extra weight per year.
However, the signals can be reactivated through drugs that have already been developed to help obese people lose weight.
It means that medication could be given to people in their twenties or thirties to regulate appetite.
"It could be used as a preventative and stop the middle-aged spread altogether," said Professor Lora Heisler, chair in human nutrition at the University of Aberdeen, where the study was conducted.
A small set of cells in the brain are responsible for producing hormones called pro-opiomelanocortin (POMC) peptides which regulate appetite and body weight.
However, as people approach middle age those cells stop sending as many signals, and it is harder to feel full. The extra food and drink consumed could result in a normal person carrying an extra 20 to 30lb by middle age.
A new drug, lorcaserin, which is available in the US, can switch the signal back on fully, but it is not yet licensed in the UK or Europe.
"Many people wonder why the middle-aged spread happens. You think to yourself, 'I haven't changed anything but I am gaining weight," added Prof Heisler.
"More than half of people in the UK are overweight and one in four is clinically obese. And the fact of the matter is it is very hard to lose weight once it is there, so if we could help people before they get to that stage then that is obviously beneficial. The NHS could use this as part of a multiple strategy approach."
In the UK more than one third of men and women will be clinically obese by 2030, costing the NHS an extra pounds 19.2 billion a year.
Tam Fry of the National Obesity Foundation said the drugs could help overweight people but advised against giving them to young people before they gained weight.
"We're heading in the right direction and drugs like this could be the Holy Grail in fighting the obesity epidemic," he said.
"But the problem with the middle-aged spread is that it is caused by a number of factors. The real answer is that if you exercise and eat healthily then a lot of these problems will go away. People need to be self-controlled and not rely on medication."
— The study was published in the journal Endocrinology.