Conventional wisdom says you need to worry about your diet only if you’re overweight, but new research finds that eating too many energy-dense foods, such as hamburgers and pizza, can still raise your cancer risk, regardless of your body mass index (BMI). This study comes on the heels of recent research that indicates even thin people can be metabolically unhealthy if they consume a high-calorie diet.

Eating large quantities of these foods was associated with a 10 percent increase in obesity-related cancers among postmenopausal women who were a normal weight. According to lead investigator Cynthia A. Thompson in a recent statement, this suggests that weight control and management may not be enough to protect against obesity-related illnesses and cancer if women are eating the wrong types of food.

"Among normal-weight women, higher DED [dietary energy density] may be a contributing factor for obesity-related cancers," explained Dr. Thomson. "Importantly, DED is a modifiable risk factor. Nutrition interventions targeting energy density as well as other diet-related cancer preventive approaches are warranted to reduce cancer burden among postmenopausal women."

Being overweight or obese has long been recognized as a major risk factor for several types of cancer. According to the Centers for Disease Control and Prevention, about 3.5 percent of new cases of cancer in men, and 9.5 percent of new cancer cases in women, were to due to overweight or obesity in 2012. This percentage varied depending on the type of cancer; for example, about 54 percent of female gallbladder cancer cases in 2012 were attributed to being overweight or obese.

Although it's not clear why obesity is linked to so many different types of cancer, researchers believe it may be due, in part, to the chronic state of inflammation obesity causes throughout the body. This disturbs the normal production of certain hormones, which can, in turn, increase cancer risk.

However, this new research suggests that eating poorly, without being overweight or obese, can still lead to certain cancer risk increases. For the study, the team of researchers used data on 90,000 postmenopausal women from the Women's Health Initiative, including their diet and any diagnosis of cancer. Based on these results, the study hypothesizes that weight gain alone may not be responsible for increased cancer risk. Instead, the types of foods eaten, which can lead to weight problems, may cause a disruption in metabolism that is responsible for increased cancer risk.

There are a number of limitations to this study, as it used data only from postmenopausal women. We can't say how these energy-dense foods may affect other healthy weight demographics. Still, the results suggest that postmenopausal women may want to look after their diet, even if they are already a health weight.

Source: Thomson CA, Crane TE, Garcia DO, et al. Association between Dietary Energy Density and Obesity-Associated Cancer: Results from the Women's Health Initiative. Journal of the Academy of Nutrition and Dietetics . 2017