US researchers have discovered that some people who are overweight have hidden fat inside their bones that could make them weak and prone to fractures.
The Harvard Medical School team in Boston did body scans on 106 obese but healthy men and women.
The findings are published in the journal Radiology.
The scans reveal some people carry fat in hidden places like the liver, muscles and bone marrow as well as their belly, hips or thighs.
Dr Miriam Bredella, who carried out the work, says apple-shaped people who carry weight around their waist may be at greatest risk.
The bone marrow is where the cells responsible for new bone formation – osteoblast cells – live.
Dr Bredella reasons that if more of the marrow is taken over by fat cells then this will weaken the bones.
She said: “If you have a spine that’s filled with fat, it’s not going to be as strong.
“Obesity was once thought to be protective against bone loss. We have found that this is not true.”