In subjects in the highest third for genetic risk of obesity, the difference in body mass index (BMI) between those who consumed fried food four or more times a week versus one time a week was 1.0 in women and 0.7 in men, wrote Qibin Qi, PhD, of the Harvard School of Public Health in Boston, and his co-authors March 17 in BMJ.

For those in the lowest third of the genetic risk score, the corresponding differences were 0.5 and 0.4, they wrote.

The study included 9,623 women from the Nurses’ Health Study and 6,379 men from the Health Professionals Follow-up Study for whom genotype data and periodic dietary questionnaires existed.

In addition, 21,421 women from the Women’s Genome Health Study, for whom the same data was available, were included as a replication cohort. Genetic risk scores for both groups were based on 32 known BMI-associated variants.

In another analysis that combined the three cohorts, the differences in BMI per 10 risk alleles (P<0.001 for interaction) were: 1.1 for fried food less than once a week, 1.6 for fried food one to three times a week, and 2.2 for fried food more than three times a week.

In a third analysis looking at risk of obesity, the odds ratio for obesity per 10 risk alleles for the combined cohorts were:

• 1.61 (95% CI 1.40 to 1.87) for fried food less than once a week
• 2.12 (95% CI 1.73 to 2.59) for fried food one to three times a week
• 2.72 (95% CI 2.12 to 3.48) for fried food more than three times a week

“The variants in or near genes highly expressed or known to act in the central nervous system showed significant interactions with fried food consumption,” the authors said.

But it was the FTO (fat mass- and obesity-associated) variant that showed the strongest result (P<0.001 for interaction), they said. The genetic association between the FTO variant and BMI strengthened consistently across all three categories of fried food intake in all three cohorts, the authors said.

Previous studies have demonstrated that a diet heavy in fried foods is associated with obesity and chronic disease. But those studies did not, the authors said, take into account the potential modification of risk created by each individual’s genetic make-up.

These results are the first to suggest that people with a greater genetic predisposition to adiposity are more susceptible to the adverse influence of a surfeit of fried food.

The study “provides formal proof of interaction between a combined genetic risk score and environment in obesity,” said Alexandra Blakemore, PhD, and Jessica Buxton, PhD, both of Imperial College in London, in an editorial that accompanied the article.

Blakemore and Buxton said that the results of the study were unlikely to influence public health advice “because all of us should be eating less fried food,” but might herald an era of fewer one-size-fits-all approaches to treating people with obesity.

The authors of the study said that their results do suggest that it is possible to modify risk with behavioral change — particularly with regard to fried food.

“Our findings further emphasize the importance of reducing consumption of fried foods in the prevention of obesity,” in individuals known to be at genetic risk for adiposity, they said.

There were limitations in the study. Confounding by unknown factors might exist. Food frequency questionnaires might have contained errors. The authors said they were unable to test sex differences within each cohort because of the single-sex study design.

Some information regarding diet — whether fried food was consumed at home or at restaurants, the type of oil used, the type of frying and the temperature used for frying, and the number of times the oil had been reused — was not available. This could have limited the depth of analyses, the authors said.

Finally, given that the study participants were middle-age adults of European ancestry recruited in the U.S., it is unknown, said the authors, whether the results can be generalized to other demographic and ethnic groups.

• Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania

LAST UPDATED 03.19.2014