Too much sugar can lead to weight gain. But for certain people, poor production of the hormone dopamine in their brain might also promote overeating, pushing them toward diabetes and obesity. The finding complements the latest understanding of how foods high in sugar and fat can hijack the brain’s reward system, motivating people to overeat.

A study published in June 2013 compared individuals whose cells process insulin normally with other subjects whose cells resist insulin. Insulin controls how glucose is delivered into cells, giving them energy. Subjects who were insulin-resistant produced a lower amount of dopamine after drinking a sugary beverage than individuals who process insulin normally. Brain scans showed that both groups of people had similar numbers of dopamine receptors in cells in their brain reward centers, which ruled out lower uptake of dopamine as a potential factor.

The reward centers help motivate people to seek foods high in sugar and fat. Insulin resistance in association with less dopamine in those reward centers might cause people to overeat, to compensate for obtaining a lesser sense of satisfaction from eating sugary food, according to the study’s lead researcher, Gene-Jack Wang, professor of radiology at Stony Brook University and a researcher at Brookhaven National Laboratory in Upton, N.Y.

Medical complications can arise when cells resist the uptake of insulin; in response, the body produces more insulin while glucose levels are high in the blood stream. That pairing is a major contributor to metabolic syndrome, a precursor to diabetes that also often accompanies obesity.

Previous studies have shown similar effects in mice, but Wang says his study is the first to reveal them in humans. Only 19 people participated in his trial, but if larger studies confirm the mechanism, Wang says medication could possibly be developed to help insulin-resistant people counteract their low output of dopamine.