Obesity Linked To Abnormal Response To Sweet Foods, Researchers Say

A new study has recently revealed that food preference change as age increases. Researchers found that age and receptor levels of reward-associated chemical dopamine influence preference for sweet foods among people of a healthy weight, but not for people who are obese.

According to an article in Medical News Today, first author M. Yanina Pepino, Ph.D., of the Washington University School of Medicine and colleagues' found from a small study of adults ages 20 to 40 years old showed that the brain's reward system functions differently in people who are obese compared to thinner people, which researchers believe may play a part in the 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," Pepino said. "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."

Science Daily reported that the subjects of the study were given drinks which contained different levels of sugar to determine the degree of sweetness each one liked. Then, the researchers conducted a PET scan to identify dopamine receptors linked to rewards in each person's brain. Dopamine is the chemical in the brain that makes people feel good.

The scans show that even though there was a direct relationship between the dopamine receptors, preference for sweet things and age in lean people, that pattern didn't hold true in the brains of obese people.

"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," says co-investigator Tamara Hershey, a professor of psychiatry, neurology, and radiology, futurity.org reported.

Pepino and Hershey said it's possible that insulin resistance or some other metabolic changes related to obesity could have contributed to the absence of those associations in the obese group. Though none of the obese study participants had diabetes, some had high glucose level in the blood as well as insulin concentrations, and some were developing resistance to insulin. The researchers think those factors could have changed the brain's response to sweet things.

"There is a relationship between insulin resistance and the brain's reward system, so that might have something to do with what we saw in obese subjects," Hershey says. "What's clear is that extra body fat can exert effects not only in how we metabolize food but how our brains perceive rewards when we eat that food, particularly when it's something sweet."