Scientists have found a gene that makes us crave sweet and fatty foods and pile on the pounds when under stress.
The 'comfort eating gene' has also been linked to type 2 diabetes - the form of the disease that usually occurs in middle-age and is related to obesity.
It is hoped that studying the gene will lead to new diabetes drugs as well as weight loss pills.
But it seems finding time to relax could also do us the power of good.
Researcher Dr Alon Chen set out to find out why so many people reach for the biscuit tin when under pressure at home or at work.
In studies on mice, he pinpointed a gene that pumps out a protein called Ucn3 at times of stress.
Produced in the brain, the protein has profound effects throughout the body, affecting organs including the heart, muscles, liver and pancreas.
It increases appetite and affects how full we feel as well as the way the body uses insulin, a hormone crucial in the processing of sugar into energy.
Mice that were made to make more Ucn3 than usual began to show the first signs of diabetes, the journal Proceedings of the National Academy of Sciences reports.
Ucn3 also seems to trigger a taste for sugary and fatty foods - providing the body and brain with extra fuel when under extreme stress.
But when the system is constantly activated by everyday stresses and strains, we can become fat and ill.
Dr Chen, of the Weizmann Institute-in Israel, said: 'Stress is good when you have to cope with an event, like when you meet a lion.
'Your metabolism is changing, you consume more sugars and more glucose goes to the muscles to help you escape the lion.
'But the stress response needs to be a tightly-regulated system.
The genes need to kick in at the right time. If they are not working properly it can lead to psychiatric and metabolic disorders.'
Drugs that target the 'comfort eating gene' or the Ucn3 protein could help prevent diabetes and keep weight down.
Previous work by British researchers has shown that almost two-thirds of people in the UK carry other 'junk food genes' that cause them to crave fatty and sugary foods.
Those with the genetic flaw eat 100 calories more at each meal - the equivalent of a Kit Kat or a bag of Wotsits.
Over the course of a week, that amounts to an extra 2,100 calories - or an extra day's food.
The findings, by researchers at Dundee University, help explain why some people find it hard to resist fast food - and why some diets are doomed to fail.
Britons are also the world's worst junk food addicts, beating even the Americans in their appetite for fat and sugar-laden snacks.
Figures show the average adult in this country eats just over three portions of fruit and vegetables a day and will get through 22,000 ready-meals, sandwiches and sweet snacks in a lifetime - little short of one a day." According to DAILYMAIL reports.