Hold the gym membership: Those who blame a lack of exercise for weight gain are at GREATER risk of piling on the pounds Overweight people are more likely to think lack of exercise causes obesity Those who are a healthy weight tend to believe diet causes weight gain Researchers say findings show link between people's beliefs and their size If you believe that exercise is the key to losing weight rather than your diet, you may want to think again. A new study has found the majority of overweight people believe lack of exercise is to blame for them piling on the pounds instead of overeating. But in sharp contrast, people who are slim or have a healthy weight think diet is the main cause of obesity. Researchers say the findings show that people's belief on what causes obesity has a direct impact on their weight - claiming they can even predict body mass index (BMI) by their views. Researchers believe they have found a link between people's beliefs about what causes obesity and the size of their waistlines - with those who think lack of exercise is to blame generally being more overweight and having poorer diets than those who thought diet was the main cause People who believe lack of exercise is the main cause of obesity are generally more overweight and eat far more chocolate than those who believe the opposite. Researchers Doctor Brent McFerran, of the Ross School of Business at the University of Michigan, and Doctor Anirban Mukhopadhyay, of Hong Kong University of Science and Technology, wondered whether individual beliefs might play a role in these trends. From an initial online survey, they discovered that people seem to subscribe to one of two major beliefs about the primary cause of obesity - that lack of exercise or overeating was to blame. Dr McFerran said: 'There was a clear demarcation - some people overwhelmingly implicated poor diet, and a roughly equal number implicated lack of exercise. Genetics, to our surprise, was a far distant third. All in the mind: Overweight people tend to believe exercise is the most important factor when losing weight They conducted a further series of studies across five countries on three continents to see if they could discover a link between people's beliefs and their weight. Data from participants in Korea, the U.S. and France showed the same overall pattern - people who implicated diet as the primary cause of obesity actually had lower BMIs than those who implicated lack of exercise. Dr McFerran said: 'What surprised me the most was the fact that we found lay theories to have an effect on BMI over and above other known factors, such as socio-economic status, age, education, various medical conditions, and sleep habits.' The researchers hypothesised that the link between people's beliefs and their BMI might be linked to how much they eat. A study with Canadian participants revealed that participants who linked obesity to lack of exercise ate significantly more chocolates than those who linked obesity to diet. And a study with participants in Hong Kong showed that participants who were primed to think about the importance of exercise ate more chocolate than those primed to contemplate diet. The research team said their findings provide evidence that our everyday beliefs about obesity may actually influence our eating habits - and our weight. Dr Mukhopadhyay added: 'This is the first research that has drawn a link between people's beliefs and the obesity crisis, which is growing as fast as people's waistlines are.' He said the new findings suggest that, in order to be effective, public health campaigns may need to target people's beliefs just as much as they target their behaviour. The results were published in the journal Psychological Science.