Time to be lean as new studies show all forms of obesity increase cancer risk

New studies reveal that both the metabolically healthy and unhealthy ‘forms’ of oesity are linked to an increased risk of several obesity-related cancers, with the association being more potent in metabolically unhealthy obesity. The studies were published in the Journal of the National Cancer Institute. Dr. Ming Sun, of Lund University in Malmo, Sweden, and colleagues conducted the study.

There aren’t many studies on the connection between obesity and cancer, either healthy obesity or obesity with metabolic issues (often referred to as metabolically unhealthy obesity). In this new study, the scientists examined the relationship between metabolic health status and body mass index (BMI, normal weight/overweight/obesity) concerning obesity-related cancer risk (n=23,630) in 797,193 European people.

Statistical modelling was employed to determine any association between a metabolic score that included blood pressure, plasma glucose, and triglycerides (blood fats) to identify metabolically healthy and unhealthy conditions.

The participants thus were put into six different categories – metabolically unhealthy obesity (6.8 per cent of participants); metabolically healthy obesity (3.4 per cent), metabolically unhealthy overweight (15.4 per cent), metabolically healthy overweight (19.8 per cent), metabolically unhealthy normal weight (12.5 per cent), metabolically healthy normal weight (42.0 per cent).

Metabolically unhealthy obesity, was, compared to metabolically healthy normal weight, associated with an increased relative risk of any obesity-related cancer and colon, rectal, pancreas, endometrial, liver, gallbladder, and renal cell cancer, with the highest risk estimates for endometrial, liver, and renal cell cancer (2.5 to 3.0 times increased risk).

In women, compared to metabolically healthy women of normal weight, metabolically unhealthy women with obesity had a 21 per cent increased risk of colon cancer, a 3-times increased risk of endometrial cancer, and 2.5 times increased risk of kidney cancer. Metabolically healthy women with obesity had 2.4 times increased risk of endometrial cancer and an 80 per cent increased risk of kidney cancer – but the relationship with colon cancer was no longer statistically significant.

In men, compared to metabolically healthy men of normal weight, metabolically unhealthy men with obesity had 2.6 times increased risk of kidney cancer, an 85% increased risk of colon cancer, and a 32 per cent increased risk of both pancreatic and rectal cancer. Metabolically healthy men with obesity had a 67 per cent increased risk of kidney cancer, and a 42% increased risk of colon cancer, but the relationship with both pancreatic cancer and rectal cancer was no longer statistically significant. In an unusual finding, both metabolically healthy and unhealthy men with overweight (not obesity) had around a 50 per cent increased risk of the blood cancer multiple myeloma – yet neither metabolically healthy or unhealthy men with obesity had an increased risk of this cancer.

The authors say that, among men only, the data suggest that obesity jointly with metabolic complications increases the risk of these obesity-related cancers more than expected from the sum of either risk factor individually. They say: “This has important public health implications, suggesting that a significant number of cancer cases could potentially be prevented by targeting the co-existence of metabolic problems and obesity, in particular for obesity-related cancers among men.”

The authors conclude: “This study highlights that the type of metabolic obesity phenotype is important when assessing obesity-related cancer risk. In general, being metabolically unhealthy further increased the obesity-related cancer risk, suggesting that both obesity and metabolic conditions are useful targets for the prevention of obesity-related cancers.”