“Our findings indicate that traditional metrics, such as the body mass index (BMI), may underestimate the risk of excess body fat and that only by utilizing more precise tools can we uncover a higher proportion of breast cancer cases linked to excess fat,” states study author Verónica Dávila Batista, a physician and doctoral candidate at the University of Las Palmas de Gran Canaria (Canary Islands).
According to scientists, obesity, traditionally determined by BMI, is associated with approximately 10 percent of breast cancer cases in postmenopausal women.
However, the body mass index may not be the most accurate method for assessing excess fat and obesity, as it only takes height and weight into account, explains Dr. Dávila Batista.
In this study, researchers aimed to determine if a more accurate assessment tool could better predict the increased risk of hormone-positive breast cancer.
Similar to BMI calculations, this tool uses height and weight, but it also considers age and sex, which are crucial for calculating body fat levels. Numerous studies have shown that this tool, the Body Adiposity Estimator developed at the University of Navarra Clinic (Clínica Universidad de Navarra–Body Adiposity Estimator, CUN-BAE), better predicts metabolic and cardiovascular risks; however, this is the first study where it has been applied to assess cancer risk.
The study included 1,033 women diagnosed with breast cancer and 1,143 postmenopausal women without breast cancer (the control group).
Researchers controlled for several factors that might influence the risk of breast cancer, such as diet, alcohol consumption, smoking, and medical and reproductive history.
When researchers used BMI to predict breast cancer risk, obesity accounted for 19.9 percent of postmenopausal breast cancer cases, but when using the CUN-BAE tool, this figure rose to 41.9%.
Researchers found that as the percentage of body fat increased, the associated risk also rose.
If women had 35-39.9% body fat, the risk of developing breast cancer increased by about 50% compared to women with a low percentage of body fat; among women with more than 40% body fat, the risk more than doubled.
Why does excess fat increase the risk of breast cancer? Before menopause, the ovaries are the primary source of estrogen in the body. After menopause, peripheral tissues—primarily fat—become the main source of estrogen.
Excess body fat can lead to low-level chronic inflammation and cause metabolic changes in adipose tissue, which increases estrogen production and may contribute to the development of cancer.
“As a result, higher levels of body fat create conditions that increase the likelihood of developing breast cancer, especially after menopause,” explains the researcher.
The findings suggest that traditional metrics such as BMI may significantly underestimate the oncological burden linked to obesity, particularly in cases of hormone receptor-positive breast cancer.