Belly fat may release more of a protein that can cause a non-cancerous cell to turn into a cancerous one, new research has found.
Obesity has been linked to several types of cancers including that of the breast, colon, prostate, uterus or kidney, but the new study, published in the journal Oncogene, indicated that just being overweight is not necessarily the best way to determine risk.
"Our study suggests that body mass index, or BMI, may not be the best indicator," said lead author Jamie Bernard, Assistant Professor at Michigan State University in the US.
"It's abdominal obesity and, even more specifically, levels of a protein called fibroblast growth factor-2 that may be a better indicator of the risk of cells becoming cancerous," Bernard added.
There are two layers of belly fat. The top layer, known as subcutaneous fat, lies right under the skin. The layer under that, called visceral fat, is the one she found to be more harmful.
Bernard and her co-author Debrup Chakraborty, a postdoctoral student in her lab, studied mice that were fed a high-fat diet and discovered that this higher-risk layer of fat produced larger amounts of the fibroblast growth factor-2, or FGF2, protein when compared to the subcutaneous fat.
They found that FGF2 stimulated certain cells that were already vulnerable to the protein and caused them to grow into tumours.
Bernard also collected visceral fat tissue from women undergoing hysterectomies and found that when the fat secretions had more of the FGF2 protein, more of the cells formed cancerous tumours when transferred into mice.
"This would indicate that fat from both mice and humans can make a non-tumorigenic cell malignantly transform into a tumorigenic cell," Bernard said.
There are several other factors released from fat, including the hormone estrogen, that could influence cancer risk, but many of those studies have only been able to show an association and not a direct cause of cancer, Bernard said.
Genetics too play a role, she added.