New research shows that brain responses to written food words differ between lean individuals and those with obesity, and suggests that both stress and genetics could influence excess eating.
The pair of studies led by Susan Carnell, PhD, member of The Obesity Society (TOS) and Assistant Professor of Psychiatry and Behavioral Sciences at Johns Hopkins University School of Medicine, reinforces the need to better understand how the external food environment interacts with our biology, and may aid the development of behavioral interventions to help individuals with obesity or those at high risk for the disease. The findings will be unveiled during an oral presentation on Nov. 3, and a poster presentation on Nov. 4, at The Obesity Society Annual Meeting at ObesityWeekSM 2015 in Los Angeles, CA.
In recent years, obesity researchers have greatly enhanced our understanding of "food cues," which are internal or external environmental factors that influence the desire to eat. They come in many forms including emotions, images, smells, tastes and even food words. Food words could be considered a relatively minimal food cue compared with images or smells; however, because they are ubiquitous in advertising and other contexts they have significant potential to impact eating behavior.
In one study, the research team found that individuals with obesity were more likely to consume energy-dense foods (foods high in calories per unit of weight) compared to those of normal weight after experiencing stress. As seen in brain imaging scans, neural responses to high-calorie compared with low-calorie food words was also increased for individuals with obesity under both stressed and non-stressed conditions. To conduct the study, seventeen participants with obesity and 12 at normal weight underwent a functional magnetic resonance imaging (fMRI) scan during which they viewed words describing high-calorie foods, low-calorie foods and non-foods, and rated how much they wanted to eat each food item.
"Our study found that individuals with obesity had a stronger response to words associated with high-calorie foods -- such as chocolate spread and chicken wings -- in a widespread neural circuit spanning multiple areas of the brain," said Dr. Carnell. "When we subjected individuals to a combined social and physiological stressor, both individuals with obesity and those of normal weight showed slightly altered responses to high-calorie food words, but only those with obesity ate more at a subsequent meal. This suggests that people with obesity show a consistently different response to mere words describing foods than lean individuals. This could contribute to excess intake of energy-dense foods in both stressful and non-stressful environments."
In the second study, the research team identified an association between higher genetic obesity risk in teenagers based on several known obesity-associated genetic variants and subjective responses to food words. In addition, one specific genetic variant, MC4R, was associated with greater intake of high-calorie foods during a laboratory test meal, while another, FTO, was associated with lower scores on a questionnaire measuring self-regulation of food intake.
A genetic variant is a genetic difference that makes one individual or population different from another.
"We all have tiny differences in our genome that affect how we interact with the surrounding environment," says Carnell. "While some of the genetic variants we see may have helped people maintain a healthy body weight in the past, they could now be working against us, making certain populations more susceptible to obesity and diabetes."
To conduct the study, the research team genotyped 35 adolescents between 14 and 19 years old with varying familial risk for obesity. Subjective appetite responses to food and non-food words were measured using a computer paradigm, and food consumption was measured in a laboratory meal that followed. Participants also filled out a questionnaire measuring habitual self-regulation of intake.
"While we know that certain genetic variants are tied to obesity, our study provides additional insight into how these particular obesity-associated genetic variants may be working -- by increasing appetite and food intake," said Leora Benson, MS, research coordinator for the study. "The fact that many of these genetic variants act through eating behavior is exciting because behavior can be changed," adds Carnell. "This research tells us that there may be ways we can help prevent individuals with these variants from developing obesity."
The new understandings gleaned from these two studies could help the clinical research community identify behavioral treatment strategies based on reducing the impact of food cues, particularly for those at high risk for obesity.
"It may be possible to train our brains to react differently to certain food cues," said Martin Binks, PhD, FTOS, Secretary Treasurer of and spokesperson for The Obesity Society. "This research is a step toward better understanding how food words -- relatively minimal food cues -- may influence food consumption and how other common experiences like stress may interact with associated food cues to influence eating behavior. These types of studies may eventually lead to more effective behavioral strategies."
The Obesity Society calls for more research into neurohormonal regulation of eating behavior.
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