Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Nonalcoholic Steatohepatitis ?
    ### Response:
    Although NASH has become more common, its underlying cause is still not clear. It most often occurs in persons who are middle-aged and overweight or obese. Many patients with NASH have elevated blood lipids, such as cholesterol and triglycerides, and many have diabetes or prediabetes, but not every obese person or every patient with diabetes has NASH.
    