Fatty liver disease - a condition characterized by a build-up of fat in the liver - affects a quarter of the world's population. Although it commonly develops in overweight and obese people, many individuals with a body-mass index of less than 25kg/m2 will develop the disease, and tend to have worse outcomes compared to obese patients.
Professor Jacob George, the co-lead researcher of the study, said, "Cases of lean fatty liver disease are considered a bit of a mystery, as we don't know how and why the disease develops and progresses.
"Our research team compared the metabolism, gut bacteria, and genetic profiles of patients with lean and non-lean fatty liver disease to determine factors that contribute to disease development and progression.
"Interestingly, lean fatty liver patients have a very distinct metabolism compared to non-lean ones, which can explain some of the differences we see in disease progression.
"Compared to non-lean patients, lean patients had higher levels of bile acids, which play a role in the digestion of fats, and a protein called fibroblast growth factor 19 (FGF19). Bile acids and FGF19 increase energy expenditure, which can explain why lean individuals with fatty liver disease stay lean. This suggests that lean patients with a fatty liver may have an 'obesity-resistant' profile and better adaptation to an excess intake of calories."
Associate Professor Mohammed Eslam, the co-lead researcher, added, "Importantly, the favorable profile of lean patients did not protect them from liver fat accumulation.
"We also identified changes in particular gut bacteria and novel genes that can influence the development of fatty liver disease in lean patients. For example, we identified that a variant in the gene TM6SF2, previously linked to fatty liver disease, is more common in lean patients."
Without treatment, fatty liver disease can result in liver scarring, liver cirrhosis, and, in severe cases, liver failure.
Associate Professor Mohammed Eslam said, "The adaptive metabolic mechanisms in lean fatty liver disease tend to be lost in the late stages of the disease. This could explain why these patients have worse disease outcomes compared to their obese counterparts."
"Now that we know more about the metabolic profile and processes behind the fatty liver disease in lean people, we can work towards more targeted treatments for these patients."
Professor George concluded, "Our research is now focused on understanding more about the condition so that we can prevent its progression, and develop more personalized treatment regimens."