Quick! What’s the cause of obesity — a lack of exercise or overeating?

Your answer might be a reflection of your current body shape.

Researchers from the Ross School of Business at the University of Michigan and Hong Kong University of Science and Technology found that people who believe diet is most implicated in obesity have a lower BMI (body mass index, one screening tool used by health professionals to determine possible weight problems). Those who believe lack of exercise is behind obesity tended to have a higher BMI.

BMI is a slightly controversial screening tool, as it doesn’t take into account actual body fat readings, but instead relies on height and weight to determine a person’s risk. To find your BMI, click here.  A lower BMI generally means a lower body weight.

The study, published in Psychological Science (the journal of the Association for Psychological Science), found that data from those surveyed in the United States, Korea and France showed the same patterns — if study participants believed diet was the culprit of being overweight, they tended to weigh less than those who believed exercise was key.

The study authors said that surveyed Canadians who thought exercise played the major role in weight ate significantly more chocolates than those who linked obesity to diet, as did those from Hong Kong.

As a personal trainer, I often struggle to help clients realize they can’t exercise away a poor diet. They kill it in the gym and get fitter, but unless they change their eating patterns the scale doesn’t budge much. Exercise helps people lose weight — and, importantly, maintain their weight — but real weight-loss results come with dietary changes.