How much fat builds up in the body and where it is distributed can be linked to different risks of cancer for men and women, new research suggests.
The obesity-related risks also vary across cancer types, like bowel, oesophageal, and liver cancer.
While obesity has been previously linked to an increased risk of cancer, most studies have not differentiated the risks between male and female patients, researchers say.
However, the new study suggests that both overall fat accumulation and fat distribution in different parts of the body confer different cancer risks depending on sex.
The findings also indicated a difference in the effect of obesity on cancer risk between post- and pre-menopausal women.
An important aspect of obesity-associated disease risk is the distribution of fat in different compartments of the body— Asa Johansson, Uppsala University
First author Mathias Rask-Andersen, a researcher at Uppsala University in Sweden, said: “Doctors and scientists are aware that obesity increases cancer risk, but this connection is less well known to members of the public.
“These observations are important for risk assessment and to gain a deeper understanding of adiposity-related disease risks.”
Senior author Asa Johansson, also of Uppsala University, said: “An important aspect of obesity-associated disease risk is the distribution of fat in different compartments of the body.
“Fat stored in the abdomen is considered more pathogenic compared to subcutaneous fat.
“In addition, the amount of fat stored in different compartments, as well as the rates of most cancers, is known to differ between females and males.
“These facts motivated a careful sex-stratified analysis of adiposity-related cancer risk.”
According to the study, in women the strongest links between overall fat accumulation and cancer were in gallbladder cancer, endometrial cancer, and oesophageal adenocarcinoma.
In men the strongest links between overall fat accumulation and cancer were in breast cancer, hepatocellular carcinoma – a type of liver cancer – and renal cell carcinoma.
In terms of fat accumulation and distribution, there were differences between the sexes for colorectal (bowel), oesophageal, and liver cancer.
The study, published in the Cancer Cell journal, suggests that a larger proportion of fat stored in the abdomen is associated with oesophageal squamous cell carcinoma in females but not in males, while body fat accumulation is associated with a high risk for hepatocellular carcinoma in males, an effect that is not present in females.
Ms Johansson added: “We were surprised to see that there appeared to be a difference in the effect of obesity on cancer risk, not only between males and females, but also between post- and pre-menopausal females.
Obesity is only a risk factor for breast cancer after menopause, probably due to the change in oestrogen production in association with menopause— Asa Johansson, Uppsala University
“Most remarkable, obesity is only a risk factor for breast cancer after menopause, probably due to the change in oestrogen production in association with menopause.”
The investigators used data from the UK Biobank, a cross-sectional cohort of 500,000 UK residents aged between 37 and 73 who were recruited between 2006 and 2010.
They were followed for an average period of 13.4 years.
Among the data collected were details about the distribution of fat in their bodies and whether they developed cancer.
A separate study, published in Nature Metabolism, looked at the link between obesity and how the brain responds to nutrients.
It found that the brain’s responses to specific nutrients are diminished in obese people, and do not improve after weight loss.
The findings suggest that long-lasting brain changes may take place in people with obesity, which could affect eating behaviour.
In the study, researchers Mireille Serlie, from Yale University School of Medicine in the US, and colleagues infused specific nutrients directly into the stomachs of 30 people with a healthy bodyweight, or 30 people with obesity (a BMI of 30 kg/m2 or above).
Their brain activity was measured at the same time.
The researchers found that those with a healthy bodyweight displayed specific patterns of brain activity and dopamine release after nutrient infusion.
However, these responses were blunted in people with obesity.
Additionally the study found that a 10% body weight loss (following a 12-week diet) was not sufficient to restore these responses in people with obesity.
The researchers say this suggests long-lasting brain changes occur in the context of obesity and remain even after weight loss is achieved.
