NEW YORK (GenomeWeb) – People who are at higher genetic risk of becoming obese may benefit the most from sticking to a healthy diet, according to a new study.
The number of people who are obese has tripled since 1975 and about 671 million adults worldwide are affected. Researchers from Tulane University and elsewhere examined genetic, diet, and body mass data from two large longitudinal studies in the US to determine how those factors interact with one another. As they reported in the BMJ yesterday, the researchers found that people at increased genetic risk of becoming obese who started to follow a healthy diet lost weight and lowered their body mass index — more so than people who didn't have a high genetic risk of obesity.
"Our findings highlight the importance of improving adherence to a healthy diet in the prevention of weight gain, particularly in people genetically predisposed to obesity," Tulane's Lu Qi and his colleagues wrote in their paper.
However, the researchers also cautioned that their study was observational and could be influenced by unmeasured confounding factors.
For their study, Qi and his colleagues drew upon data collected by the Nurses' Health Study and the Health Professionals Follow-Up Study on 8,828 women and 5,218 men of European ancestry for whom genotyping data was available. At baseline, none of the participants had diabetes, cancer, or cardiovascular disease.
Every four years, participants provided their weight, which was used to calculate their BMI using the height they gave at enrollment. They also answered questionnaires about the foods they ate.
To determine participants' genetic predisposition to obesity, the researchers generated a genetic risk score based on 77 SNPs that have been associated with BMI among Europeans. They weighted the contribution of each SNP to the risk score by its relative effect size on BMI.
Overall, the researchers noted that participants' genetic risk score was associated with increases in their BMI and weight over the study period. In particular, they found that each additional 10 risk alleles was associated with a 0.02 increase in BMI and 0.11 pound increase in weight.
At the same time, Qi and his colleagues assessed the participants' diets using three measures of healthy eating: the Alternation Healthy Eating Index 2010, the Dietary Approach to Stop Hypertension, and the Alternate Mediterranean Diet scores. The scores broadly focused on participants' intake of vegetables, fruit, and whole grains.
The association that the researchers found between genetic risk scores and BMI or weight was attenuated by hewing to AHEI-2010 or DASH diets. For instance, those in the lowest third of participant AHEI-2010 scores had a 0.07 increase in BMI per 10 risk alleles, while those in the highest third of AHEI-2010 scores had a 0.01 decrease in BMI per 10 risk alleles. That, the researchers noted, works out to a 0.35-pound increase in weight versus a 0.04-pound decrease in weight. A similar pattern was seen for DASH diet scores, though not for AMED scores.
Improving how well people stick to a healthy diet could modify their genetic risk of becoming obese, Qi and his colleagues said.
They noted, though, that this was an observational study with a number of limitations. For instance, the biological mechanisms that underlie what they observed are not yet known, confounding factors such as physical activity could also have a role, and participants were of European descent.
Further, in an accompanying editorial in the BMJ, University Hospitals of Geneva's Nathalie Farpour-Lambert and her colleagues noted that the effect of genetic predisposition was small. "However, the findings provide encouraging new evidence that although a better diet can improve weight loss, the effect may be greatest in those with the highest genetic predisposition for obesity," they added.