Many of my patients have decried the fact that they have had to battle obesity their entire lives, as have their parents, their siblings and most of their ancestors. I’ve been tempted to make light of their weight plight and reassure them by suggesting that they and their predecessors were at least genetically programmed to survive famine and pogroms whereas those of us who are thin, were in a Darwinian sense, not endowed with “survival” fat. Well, current research indeed shows that many of the families who are overweight, have a distinct genetic predisposition for their obesity. Although this may help make those who face genetic obesity feel vindicated, the hypothesis that this provided protection in the past, does not lessen their struggle to be healthy and fit into their clothes in the present. Obesity has increased to epidemic proportions and even if only some individuals have underlying genetic propensities, we should all be interested in the article that came out in the October 11 issue of JAMA titled “Sugar-Sweetened Beverages and Genetic Risks of Obesity”.
In the last few years, there have been many large-scale studies investigating the presence of loci or segments in our genes that are associated with body mass index (BMI). (Just a reminder, BMI is calculated based on weight in kilograms divided by the square of the height in meters. A BMI of 30 or higher is classified as obese.) A compilation or meta- analysis of many such studies of the genomes of individuals who are obese compared to those who are not, has found 32 gene loci that are significantly associated with BMI; in other words having some or all of these loci in your genome contributes to a genetic predisposition for obesity. And now that there is a known set of genetic “influencers” for obesity, investigators are studying the interaction between environmental factors and these genes
The study published in JAMA included 6934 women from the Nurses Health Study and 4423 men from the Health Professionals Follow-up Study as well as 21,740 women from the Women’s Genome Health Study. The investigators calculated the genetic- predisposition score of the study participants based on the presence of the 32 BMI associated loci and then examined the sugar-sweetened beverages that were consumed by these groups. They went on to calculate how, in the presence of high scores, these beverages affected BMI.
Just a few words about the group: The Nurses Health Study consists of a prospective study of 121,700 female registered nurses who were 30 to 50 years old at the inception of the study in 1976. The Health Professional Follow-up Study is a prospective study of 51,529 male health professionals in United States who were 42 to 75 years old at the inception of that study in 1986. (Don’t ask me why the former study had no male nurses and the latter no female health professionals, i.e. doctors!). The participants completed food frequency questionnaires every four years. The current analysis included initially healthy women and men of European ancestry in the first two groups for whom the necessary genotype data was available. The third study (the WGHS) is a prospective study of initially healthy US women who were 45 years of age or older and did not have any chronic diseases during the period from 1992 through 1995. These women had genotype data, and of course, responses to food frequency questionnaires.
Sugar-sweetened beverages in the study questionnaires included caffeinated colas, caffeine free colas, carbonated colas, soft drinks, and noncarbonated sugar sweetened beverages (fruit punches, lemonade, or other sugar sweetened fruit drinks). The 3 groups that were studied (called cohorts) had a similar intake of sugar sweetened beverages, between 0.33 and 0.26 servings per day. The baseline intake increased with BMI in all three cohorts. And, compared to participants with lower intake of sugar sweetened beverages those with a higher intake were younger, tended to have lower levels of alcohol consumption, physical activity, a greater intake of artificially sweetened beverages and a lower “healthy eating” score. The genetic predisposition score in the three groups ranged from 13 to 43 and averaged 29. (The score was based on how many of the predisposing obesity loci they had. This gets a little complicated but basically they selected 32 single – nuclear tide polymorphisms, called SNPs, that were part of the 32 loci; some of the SNP’s were more important or larger than others and hence the score didn’t go from 0 to 32 but went as high as 64. Obviously the higher the score the higher the risk of genetic predisposition to obesity.)
When the results were combined, the investigators found that the genetic association with BMI was stronger among participants with a higher intake of sugar -sweetened beverages than among those with a lower intake. The increase in BMI for an increment of 10 obesity risk loci was 1.0 for an intake of less than one serving per month (in other words, no increase in risk compared to those who had no sugar sweetened drinks), but 1.20 for 1 to 4 servings per month (20% higher), 1.37 for 2 to 6 servings per week (37% higher) and 1..85 for one or more servings a day (85% higher). Adjustments for dietary and lifestyle factors as well as total energy intake (calories) didn’t change the results. (In other words, they got heavier with consumption of more sugar sweetened drinks even if they exercised and dieted!)
Bottom line: Individuals with a greater genetic predisposition for obesity (look to your family) are more susceptible to the deleterious effects of sugar-sweetened beverages on their BMI. Just one or more servings of sugar-sweetened beverages per day in those with a genetic risk are almost twice as likely to increase weight when compared to less than one per month. It ‘s time to consider drinking water or even artificially sweetened drinks to quench your thirst if you are combating a ” genetic” weight problem, or perhaps any weight problem.