Washington D.C: Obese people pile on the kilos because they never grow out of their childhood sweet tooth, suggests a recent study.

As young people reach adulthood, their preferences for sweet foods typically decline. But for people with obesity, new research suggests that the drop-off may not be as steep and that the brain's reward system operates differently in obese people than in thinner people, which may play a role in this phenomenon.

"We believe we may have identified a new abnormality in the relationship between reward response to food and dopamine in the brains of individuals with obesity," said first author M. Yanina Pepino.

Pepino added, "In general, people grow less fond of sweet things as they move from adolescence into adulthood. Also, as we age, we have fewer dopamine receptors in a brain structure, called the striatum, that is critical to the reward system. We find that both younger age and fewer dopamine receptors are associated with a higher preference for sweets in those of normal weight. However, in people with obesity, that was not the case in our study."

The researchers studied 20 subjects with healthy weights and compared them with 24 people considered obese, each of whom had a body mass index of 30 or higher. The study volunteers were 20 to 40 years old.

"We found disparities in preference for sweets between individuals, and we also found individual variations in dopamine receptors, some people have high levels and some low, but when we looked at how those things go together, the general trend in people of normal weight was that having fewer dopamine receptors was associated with a higher preference for sweets," said co-investigator Tamara Hershey.

But that wasn't true in the obese subjects. The relationship between their ages, sweetness preferences and dopamine receptors didn't follow the pattern seen in people who weighed less.

Pepino and Hershey explained that it's possible that insulin resistance or some other metabolic change linked to obesity could contribute to the absence of those associations in the obese group. Although none of the obese study participants had diabetes, some had higher blood glucose and insulin concentrations, and some were becoming resistant to insulin. The researchers believe those factors could have altered the brain's response to sweet things.

The new findings are published online in the journal Diabetes.