Scientists who have traced the origins of so-called “bad” fat in the body say the discovery could help to understand and treat obesity.

A team from the Medical Research Council’s (MRC) human genetics unit at Edinburgh University discovered that visceral fat – which forms around vital organs such as the heart and intestines – originates in the embryo.

Although all fat carries health risks, hidden visceral fat is said to be a much bigger threat than subcutaneous fat, which sits under the skin.

It can increase the risk of cancer, type 2 diabetes, heart disease and Alzheimer’s disease.

In contrast, subcutaneous fat – sometimes referred to as “good” fat – can be beneficial because it provides energy, cushioning and insulation.

Professor Stephen Hill, chairman of the MRC’s molecular and cellular medicine board, said: “Visceral fat can be a silent killer because it’s possible to have a lot of it without looking fat on the outside.”

Tests on laboratory mice revealed that up to 80 per cent of visceral fat can be traced back to a single type of cell in the developing embryo.

Researchers discovered that these early fat cells express a gene called Wt1 but subcutaneous fat cells do not, suggesting that the two types of fat come from different sources. The cells were also found in the visceral fat of adult mice.

Understanding how to regulate them could lead to new opportunities for the prevention or treatment of “bad” fat around the organs, the study concludes.

Lead author You-Ying Chau said: “Determining the origins of good and bad fat has been one of the big unanswered questions in obesity research.”

The study is published in the journal Nature Cell Biology.