Kim Painter

Special for USA TODAY

A diet full of fried foods isn't good for anyone, but it may result in more weight gain for people at a high genetic risk of obesity, a new study suggests.

The study, published Tuesday in the journal BMJ, is the latest evidence that life isn't fair when it comes to navigating a world of french fries, soda and comfy sofas — because some people are genetically predisposed to become fatter than others indulging in the same bad habits.

It's a "groundbreaking concept" that could lead to more individualized prescriptions for weight control, says lead author Lu Qi, an assistant professor of nutrition at the Harvard School of Public Health.

Qi and colleagues used data from 37,000 middle-age and older adults of European descent. Participants, who were part of three larger studies, gave blood for genetic testing and, over several years, reported whether they ate fried foods less than once a week, one to three times a week or at least four times a week. Researchers also kept track of each person's body mass index (BMI), a measure of weight relative to height.

As expected, they found higher BMIs in people who most frequently ate fried foods and in those at high genetic risk, as determined by 32 genetic variations previously linked to high BMI.

But they found the highest BMIs in people who had both risk factors — suggesting genes and fried foods can "amplify each other" to add pounds, Qi says.

In previous studies, researchers found same apparent synergy between genes and two other factors: sweetened beverages and physical inactivity.

While the studies do not prove cause-and-effect relationships, they do help build the case that genes and environment are both to blame for the world's obesity problems, experts say.

"In Westernized societies, we are all exposed to calorie-dense food, sedentary lives, stress and sleep deficit. Some people seem relatively insensitive to these environmental pressures, while others are severely affected and become obese," says an editorial accompanying the study, written by Alexandra Blakemore, a professor of human molecular genetics, and Jessica Buxton, a research associate, at Imperial College in London.

People with strong genetic susceptibilities may need more than standard lifestyle advice to control weight, they write.

But the findings don't mean that people with favorable genes can eat anything they want, live a life of sloth and never suffer the consequences.

"At this point I think we should strongly recommend that everybody reduce their fried food consumption," Qi says.

In any case, testing for obesity genes wouldn't tell individuals much right now, Qi says. That's because the genes discovered so far explain just a fraction of the differences among people.

Unknown: what, exactly, these genes might do to boost weight gain. One theory is that some affect appetite — meaning one person who gets four plates of french fries a week eats them all while another throws half away. But the new study found no association between high genetic risk and increased calorie intake. That hints that the problem might be in how quickly people burn calories, even when at rest, Qi says.

"Body weight is still determined by calories in and calories out," says Christopher Ochner, an assistant professor of pediatrics at Icahn School of Medicine at Mount Sinai, New York. "If genetic makeup is not associated with eating more, the only thing left is burning fewer calories."

Ochner, who studies obesity in adolescents, says the study is a warning that some people may pay a higher price than others for poor eating habits. Most of us "don't need fancy genetic testing," to figure out if we are in that group, he says: "Just look at your mom and dad."