A new study has challenged common theories about why poor children are more likely to be overweight than children from wealthier families. Previous studies have suggested that children from poor families might not have access to nutritious food, forcing them instead to fill up on cheaper, unhealthy junk food. Other studies have argued that poorer children eat when money is available, and skip meals when it is not, which could affect their metabolism and cause them to gain weight.

However, researchers at Iowa State University have determined that a lack of food isn’t necessarily behind the weight differences. Their study examined data on about 1,031 children living in low-income households. Through interviews with the children’s mothers, the researchers determined that children who didn’t get enough food were not more likely to be overweight. Though they do not have a clear explanation for why so many children living in poorer households are overweight, the researchers hope that their study encourages more research into the issue.