Compounds formed when food high in protein and fat is cooked at high temperature - such as barbecued meats - could be a key factor in the progression of liver disease, a Melbourne researcher has found. Chris Leung, a liver specialist at the Austin Hospital, found that a diet high in the compounds - known as advanced glycosylation end-products - accelerated liver inflammation and scarring in animal studies. A high number of the compounds are created when protein and fats react to sugars at high heat, for example when barbecuing or caramelising meat. Boiling or steaming foods results in low levels of the compounds, which can also be avoided by eating fresh fruit and vegetables. Dr Leung said fatty liver disease was a ''silent epidemic'', affecting between 30 and 50 per cent of the population. The incidence rose to up to 70 per cent for patients with diabetes and high cholesterol. Patients with the disease, which can progress to liver inflammation, scarring and ultimately cancer, are currently told to exercise regularly and eat a balanced, low-fat diet high in fruit and vegetables. But Dr Leung said he wondered if advanced glycosylation end-products - previously found in elevated levels in the blood of patients with liver cancer - could be part of the problem. ''The way we process foods and the foods we eat have changed over time. There is no doubt that our consumption of fried fatty foods has increased, and they contain a lot of these compounds,'' he said. More research is planned to see if a diet low in the compounds could slow the progression of fatty liver disease in humans. The finding could also lead to the development of drugs to block their effect.