Overweight and obesity are known risk factors for several types of cancer, including those affecting the breast, bowel and liver.
But new research suggests that, for some obesity-related cancers, where fat is carried on the body may be as important as how much of it there is.
The researchers propose that a better understanding of how fat distribution across the body affects cancer risk could help identify those most at risk of developing many cancers.
For many years, body mass index (BMI) has been used as a measure of overweight and obesity. Because several cancers are linked to excess weight, physicians use BMI to help them assess a person’s cancer risk.
Now, however, a study proposes that BMI may be too crude a measure for assessing cancer risk. It suggests that where excess fat is carried on the body may be equally important in increasing or decreasing a person’s risk of developing several types of cancers.
The study, published in the Journal of the National Cancer Institute, examined the relationship between fat in five different areas of the body — the abdomen (belly), visceral fat (around organs inside the abdomen), fat on the buttocks and thighs, liver fat and pancreas fat — and risk of 12 obesity-related cancers.
Abdominal fat was linked to higher risk of three cancers, while fat on the hips and thighs was linked to a decreased risk of breast cancer and meningioma, a type of brain tumor.
Daniel Landau, MD, board-certified oncologist, hematologist and expert contributor for The Mesothelioma Center at Asbestos, who was not involved in this study, commented to Medical News Today that:
“It seems that not only does obesity matter but obesity location matters. Other studies have supported this as well. Central obesity has been an independent risk factor for issues such as diabetes, heart disease, and cancer. It is believed that central obesity in particular is associated with the worst dietary habits and with the highest risk of inflammation which are pro cancerous risks.”
To evaluate causal effects of different types of adiposity (fat) distribution with risks of obesity-related cancers, the researchers used two-sample Mendelian randomization.
This approach uses genetic instruments as proxies to investigate causal relationships. The data they used came from the UK Biobank and FinnGen.
Anton Bilchik, MD, PhD, surgical oncologist, chief of medicine and Director of the Gastrointestinal and Hepatobiliary Program at Providence Saint John’s Cancer Institute in Santa Monica, CA, not involved in this study, explained for MNT that:
“The methodology is extremely complex, using genetic tools to evaluate adiposity distribution, potential mechanisms and the relationship to different obesity related cancers.”
The five fat distribution traits investigated in the study were:
abdominal subcutaneous adipose tissue (ASAT, or belly fat)
visceral adipose tissue (VAT, the fat within the abdomen surrounding organs such as the liver, intestine and pancreas)
gluteofemoral adipose tissue (GFAT, fat in the buttocks and thighs)
liver fat
and pancreas fat.
They used the technique to evaluate how the five adiposity distribution traits:
affected the risk of 12 obesity-related cancers
affected cancer-related molecular traits, and how these affected cancer risk
and how the effects of adiposity distribution traits might be mediated by the molecular traits.
The relationship between fat distribution and cancer risk was not clear cut, but the researchers did find some causal effects.
Belly fat had the most effect on cancer risk, increasing the risk of three of the 12 cancer types investigated — endometrial cancer, esophageal cancer, and liver cancer. However, it also appeared to give protection against some types of breast cancer.
Apart from belly fat, liver fat and visceral fat increased liver cancer risk, and buttock and thigh fat reduced breast cancer and meningioma risks.
Bilchik was surprised by the reduced breast cancer risk from excess gluteofermoral fat, noting that “this is a very unexpected, intriguing finding that suggests that these cells may have anti-cancer effect through hormones such as estrogen.”
Although previous research has shown clear relationships between fat distribution and cardiovascular health, the researchers state that the “relationship is not as straightforward for cancer outcomes, with causal effects varying for the different adiposity distribution traits by cancer type.”
Landau advised that physicians should not rely on BMI.
“I think the other thing this study confirms is that BMI is not the best marker of health. I consider BMI to be ‘quick and dirty.’ It gives someone a very quick and basic idea of their health, but obesity location matters,” he told us.
The National Cancer Institute suggests several mechanisms by which excess weight may increase cancer risk, including:
adipose tissue produces estrogen, high levels of which are associated with many cancer types
people with obesity often have higher levels of insulin, which is associated with many cancers
chronic inflammation, which promotes tumor growth, is common in people with obesity
fat cells produce hormones called adipokines that can stimulate cell growth.
Losing weight can reduce a person’s risk of developing cancer. One study involving almost 60,000 post-menopausal women found that those who lost at least 5% of their body weight had a reduced risk of obesity-related cancers.
And a 2020 review, while calling for further studies, suggested that weight loss could be a powerful cancer-prevention tool.