Very. In the MedicineNet.com article by Medical Author, Dennis Lee, MD and Medical Editor, Jay W. Marks, MD, Body Fat, the Silent Killer, they report that nonalcoholic fatty liver disease is currently the most common liver disease in the US and worldwide. All stages of Nonalcoholic fatty liver disease are now believed to be due to insulin resistance, a condition closely associated with obesity. As a matter of fact, tests show in people with liver problems, the greater a person’s BMI (Body Mass Index), the greater the liver damage. It is now widely accepted that all stages of Nonalcoholic Fatty Liver Diseases (NAFLD) are due to insulin resistance, a condition closely associated with obesity.
One of our greatest concerns in this country is obesity in children. And wouldn’t you know it, so is childhood NAFLD (Nonalcoholic Fatty Liver Disease).
When Fatty Liver is left untreated, it develops into steatohepatitis, a condition where not only fat is accumulated in the liver, but there is inflammation (hepatitis) and liver cell die (necrosis) and scarring (fibrosis) occur. Fibrosis of the liver can then progress to cirrhosis of the liver, which is the last stage of nonalcoholic fatty liver disease.
Liver Health Weblog 
Obesity is such an accepted part of so many lives. I talk to people every day who have given up on trying to lose weight – often because they’d tried many many times before and had not been successful in keeping the weight off. Theres more that goes into weight loss then just food – it really takes the right motivation. I hope people with fatty liver don’t give up – there’s help and HOPE out there.