Eating fried food more than four times a week may have twice as big an effect on body mass index (BMI) for those with the highest genetic risk of developing obesity, research indicates.
In other words, genetic makeup can inflate the effects of bad diet.
In a first such study, a team of US researchers analysed interactions between fried food consumption and genetic risk associated with obesity in over 37,000 men and women taking part in three large US health trials.
"Our findings emphasise the importance of reducing fried food consumption in the prevention of obesity, particularly in individuals genetically predisposed to adiposity (fatness)," said Lu Qi, assistant professor at Harvard School of Public Health.
The researchers used food frequency questionnaires to assess fried food consumption - both at home and away from home - and a genetic risk score based on 32 known genetic variants associated with BMI and obesity.
Three categories of fried food consumption were identified: less than once a week, one to three times a week, and four or more times a week.
Genetic risk scores ranged from 0 to 64 and those with a higher score had a higher BMI.
Height and body weight were assessed at the start of the trials, and weight was requested at each follow-up questionnaire. Lifestyle information, such as physical activity and smoking, was also collected.
The researchers found consistent interactions between fried food consumption and genetic risk scores on BMI.
However, the association between fried food consumption and adiposity may vary according to differences in genetic predisposition among people.
"This work provides formal proof of interaction between a combined genetic risk score and environment in obesity," wrote professor Alexandra Blakemore and Jessica Buxton at Imperial College London in an editorial.