A recent study, published in the Journal of the Academy of Nutrition and Dietetics, suggests that energy-dense diets may increase the risk of obesity-related cancers in women, even among those of normal weight. There is strong scientific evidence that having obesity can cause at least 12 types of cancer.
Dietary energy density is the ratio of a food’s calories to its weight. “It provides a measure of overall dietary quality,” says Cynthia Thomson, Ph.D., RDN, FTOS, a professor of Health Promotion Sciences at the University of Arizona in Tucson, and the lead author on the study. Energy-dense diets include significant amounts of foods such as desserts, deep-fried foods, creamy sauces, and cheese. Low energy density diets predominantly include foods such as fruits, vegetables, fish, and legumes.
The study was framed within the Women’s Health Initiative, or WHI, an ongoing, prospective cohort investigation that focuses on strategies for preventing disease, including cancer. It involved more than 92,000 postmenopausal women between the ages of 50 and 79 years at the time of enrollment and took place over a period of approximately 15 years.
Thomson and her colleagues originally hypothesized that high dietary energy density would increase the risk of developing obesity-related cancers, especially among women who had obesity at the time of enrollment, suggesting that the impact of dietary energy density would be mediated through obesity.
At the beginning of the WHI, each of the women completed a food frequency questionnaire that estimated the calories, nutrients, and weights of the foods that they consumed regularly. The researchers calculated the women’s dietary energy density by dividing their daily caloric intake from foods (in kilocalories) by the weight of those foods (in grams). Then they categorized the women into five groups according to their dietary energy density, ranging from lowest to highest.
Twice a year during the 15-year period, the women were asked whether they had developed cancer. Reports of cancer were confirmed with medical records. Of particular interest were the 12 obesity-related cancers, as detailed in AICR’s diet and cancer report, including breast (post-menopausal), colorectal, ovarian, endometrial, renal, gallbladder, esophageal, and pancreatic cancers.
Participants also provided information about their age, race, socioeconomic status, alcohol consumption, medical history, use of medications or tobacco, physical activity, and whether their weight had changed during adulthood. The researchers calculated the women’s body mass index, or BMI, based on clinical measures of their height and weight.
During the 15-year period, 9,565 women developed one or more types of obesity-related cancers, for a total of 9,934 cases reported. The most common cancers were those of the breast, with 5,565 cases reported.
Statistical analysis revealed that women whose diets were most energy-dense had a 10 percent greater risk of developing obesity-related cancer compared to those whose diets had the lowest energy density. However, when the researchers ranked the participants according to their BMIs, they noted that the risk of obesity-related cancers associated with energy-dense diets was actually higher among women who were normal weight compared to those who had obesity.
When it comes to predicting cancer risk, we really need to look more carefully at a person’s metabolic health,” says Thomson.
Eating a diet that is low in energy density is consistent with AICR’s cancer prevention guidelines. “These data reinforce the importance of eating a predominantly plant-based diet,” says Thomson. They also suggest that while maintaining a healthy weight is important, evaluating diet quality is, too. “The impact of diet and cancer risk reduction seems to be more complex than simply controlling your body weight.”
Thomson, Cynthia A., 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 118.4 (2018): 617-626.