The body roundness index is a more accurate measure of visceral fat than BMI and is non-inferior in cancer incidence and mortality prediction, new research has found.
Obesity is a known risk factor for cancer, but BMI cannot quantify the role of obesity, especially visceral obesity, in cancer risk.
Consequently, the use of measures that better estimate visceral fat – such as waist circumference and the waist-to-hip ratio – have been explored as alternative indicators of obesity-related cancer risk.
But waist circumference and the waist-to-hip ratio are also not completely accurate measures of visceral fat, as they capture both visceral and subcutaneous adipose tissue around the waist. To address this shortcoming, a recent research study has explored the value of the body roundness index.
The BRI is calculated from an elliptical body shape model to quantify how round an individual’s body is before using eccentricity to estimate the visceral fat and total body fat percentages.
“By moving beyond conventional measures of obesity, our findings provided further evidence that body fat distribution may offer complementary insights into obesity-related carcinogenesis and support greater consideration of visceral fat in future cancer prevention, risk stratification, and clinical assessments,” the Chinese research team wrote in the International Journal of Cancer.
As part of the study, researchers used data from 470,116 participants in the UK Biobank (253,458 females, median age of 57 years). The BRI was calculated at baseline – when participants first entered the Biobank – based on the following formula: 364.2 – 365.5 x √(1 – [waist circumference in centimetres/2π]2/[0.5 x height in metres]2).
A greater proportion of participants in the highest BRI tertile (i.e., the participants with a rounder body shape) were male, had a family history of cancer, and had type 2 diabetes. These participants were also from a lower socioeconomic status, were less physically active, had a higher BMI, and consumed more red and processed meats compared to participants in the lowest BRI tertile.
There were 63,135 incident cancer cases recorded across a median follow-up of 13.7 years. After accounting for the impact of age, sex, ethnicity, socioeconomic status, lifestyle factors, dietary habits, and medical history, there was an association between BRI and overall cancer risk (hazard ratio and 95% confidence interval 1.04, 1.03-1.04), where a higher BRI increased the likelihood of developing cancer.
Thirteen site-specific cancers also displayed a positive association with BRI and the risk of developing cancer: oesophageal cancer (1.14, 1.11-1.17), stomach cancer (1.13, 1.09-1.17), colorectal cancer (1.07, 1.05-1.08), liver cancer (1.20, 1.16-1.24), gallbladder cancer (1.11, 1.06-1.17), pancreatic cancer (1.09, 1.06-1.12), breast cancer (1.03, 1.02-1.05), uterine cancer (1.31, 1.28-1.34), kidney cancer (1.17, 1.14-1.20), bladder cancer (1.05, 1.03-1.08), thyroid cancer (1.10, 1.04-1.15), and Hodgkin’s lymphoma (1.12, 1.03-1.20).
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Increasing BRI was also associated with an increased likelihood of overall cancer mortality (1.04, 1.02-1.06) and all-cause mortality (1.07, 1.05-1.09). However, there was a smaller number of site-specific cancers that also displayed an association between BRI and cancer-specific mortality – only breast cancer (1.09, 1.04-1.14) and prostate cancer (1.21, 1.12-1.31).
Both BRI and BMI had good discriminatory ability for predicting the incidence of multiple types of cancer, including stomach, liver, lung, and bladder cancers. Similarly, both obesity measures were able to predict all-cause mortality. But when BRI and BMI were compared head-to-head in terms of predicting cancer incidence and mortality, no superior metric emerged.
“Despite its limited extra predictive value beyond BMI, BRI was consistently associated with the incidence and prognosis of multiple cancers, suggesting that visceral adiposity may represent an important yet overlooked determinant of cancer risk,” wrote the researchers.
“Previous studies have indicated a positive association between visceral fat and the risk of multiple cancers. This may be attributed to metabolic dysregulation caused by excessive visceral fat, which leads to increased lipid intermediates, elevated leptin levels and leptin resistance, insulin resistance, and reduced circulating adiponectin levels.
“These metabolic disturbances are associated with enhanced cell proliferation and migration, angiogenesis, and reduced apoptosis, all of which were linked to carcinogenic mechanisms. The accumulation of visceral fat is also associated with hyperinsulinemia, with evidence indicating that insulin upregulates cellular metabolic activity, potentially leading to oxidative stress and DNA damage, thereby facilitating tumour development.”
The researchers noted that their findings may not generalise to non-European populations due to the strict inclusion criteria for the UK Biobank. In addition, BRI levels were only measured at baseline, meaning the impact of potential changes in body shape throughout the follow-up period were not captured.
“These findings may offer clinicians new reference indicators for predicting and managing cancer risk and provide a scientific basis for developing public health policies aimed at obesity control,” the researchers concluded.
