With commentary by Susan Carnell, PhD, assistant professor of psychiatry and behavioral sciences, Johns Hopkins University School of Medicine, and Martin Binks, PhD, spokesperson, The Obesity Society.
Talking about high-calorie foods such as a hot fudge sundae, chocolate spread, or chocolate chip cookies can cause nearly everyone to want that food. However, obese men and women, compared to those of normal weight, have a stronger brain response to that high-calorie food talk. People who are obese are more likely to overeat when stressed after hearing those food cues, according to new research presented at Obesity Week 2015 in Los Angeles.
"We looked at neural responses to food words," said Susan Carnell, PhD, assistant professor of psychiatry and behavioral sciences at Johns Hopkins University, who presented the study. Besides mentioning the chocolate, high-fat foods, the researchers mentioned low-fat foods, such as black cherries, watermelon, green beans, and celery sticks, as well as non-food words.
As they did so, the researchers recorded brain activity as the 17 obese participants and 12 normal weight subjects were scanned using functional MRI (fMRI) imaging. "Then we stressed them out," Dr. Carnell said, instructing them to place their hand in icy cold water while they heard the words again. They also put their hands in warm water, the non-stressed condition, and listened to the words again. "Regardless of the stress [or lack of it], obese people responded differently to food cues than lean people," she said.
The brain scans showed that in obese participants there was less activity in brain regions involving self-regulation. And while both lean and obese people responded to the cues for high-calorie foods when stressed, the obese people but not the lean people ate more at a meal following that. They could eat as much as they wanted at the meal. The obese ate to excess, while the lean people did not.
Both the obese and lean people's brains showed slightly different responses when hearing food compared to non-food words and high-calorie versus low-calorie food words on the stressor day compared to the control non-stressed day. This suggests that the stress could alter responses to food cues, Dr. Carnell said. "But to my mind," Dr. Carnell said, "the far larger brain effect was the group difference between obese and lean individuals' responses to food versus non-food and high-calorie versus low-calorie food words, whether measured on either the stress day or the non-stress day.''
The study didn't test whether those who reacted strongly to the cues had more physical reactions such as reporting more watering of the mouth or feeling like they could almost taste the food.
What Dr. Carnell can't say with certainty is which came first, the obesity or the cueing that drove food consumption. In other words, was their brain ''hardwired'' for obesity due to its tendency to respond strongly to food cues, or did the brain start reacting that way as weight was gained? Further research is needed.
In a related study of teens, Carnell wanted to research predisposition to obesity. She found that lean teens who have obese or overweight moms did show less activation to food words in a neural circuit associated with self regulation.
For now, the take-home message is awareness, Dr. Carnell said. "If you can see that pattern happening in yourself, when you see it happening, look for an alternative activity."
The research advances understanding of how food cues, especially when combined with stress, may prompt overeating, said Martin Binks, PhD, a spokesperson for The Obesity Society. The findings may trigger further research to help people avoid overeating. "It may be possible to train our brains to react differently to certain food cues," Dr. Binks said.