WIN Wyoming and WIN the Rockies

Thought Bullets
for 
 January 2004

Genetic/Environment Interactions and Obesity

How much of our body weight is determined by genetics, and how much is determined by our environment? The International Society for Behavioral Nutrition and Physical Activity (ISBNPA) wrestled with the answer to that question at its annual convention this summer in Quebec, Canada. The society gathered together some of the leading researchers on the subject and asked them to share some of their findings. For this month’s thought bullets, I share a few of the highlights of those findings with you.

• Luigi Bouchard presented the results from the Genome-Wide Analysis of Eating Behaviors in the Quebec Family Study. He stated, "We now have good evidence that differences in eating between normal weight and obese subjects are not only explained by environmental and cultural factors, but also by genetic factors." The group of researchers tried to identify genes influencing eating behaviors by using a genome scanning analysis procedure. The procedure allowed researchers to identify five chromosomal regions linked to disinhibition with eating and susceptibility to hunger. The scan analysis did not uncover any evidence of a genetic linkage to restraint and eating. Although the exact genes influencing eating behaviors have not yet been identified, researchers stated the findings from this study show promise for understanding the exact genetic mechanisms that influence the regulation of food intake.

• Claude Bouchard also presented at the conference. Bouchard is the Director of the Pennington Biomedical Research Center at Louisiana State University. He has helped to write over 500 papers on the genetic and molecular basis of obesity, including the genetic influence on physical activity. Bouchard told conference participants the influence of environment and genetics on body weight would be easy to study if both occurred separately. Unfortunately, they occur simultaneously. The interactions of genetic and environment factors produce widely varying findings in research. Highlights from Bouchard’s presentation included the following:
  • A gene has been identified in the fruit fly that determines if the fly is a "rover" or a "sitter."
  • Results from the HERITAGE Family Study demonstrated a wide variety in the maximal oxygen uptake (VO₂max) response to physical activity training. The responses aggregated by families, indicating a genetic component for the measurement.
    
    
• A third presenter at the conference was Angelo Tremblay. Tremblay is on the faculty of Medicine at the University Laval in Quebec City, Canada. During his presentation, Tremblay pointed out the genotypes in populations have not changed significantly over the last few centuries. Lifestyles have changed significantly, even within the last few decades. Tremblay defined obesity as the "genetically-determined susceptibility to environmental factors." A recent study conducted by Tremblay found adolescent girls who had a certain genotype at baseline, were significantly more likely to have increased subcutaneous adiposity over a 12-year follow-up period when compared to the girls who did not have that genotype. Adjusting for factors such as dietary fat consumption, alcohol consumption and physical activity did not influence the results. Stress-related factors did impact the results. These findings led Tremblay to hypothesize that energy uptake of food may be a result of an interaction of genotype with environmental factors, with the genetic/environmental interaction being influenced by stress.

Source: International Society for Behavioral Nutrition and Physical Activity, ISBNPA newsletter, Volume 2, Issue 1, October 15, 2003.

Compiled by Betty Holmes, MS, RD

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