What are the main causes of a fatty liver?

Many causes. I would also add that there are a number of medications (such as Methotrexate & glucocorticoids) and toxins (such as phosphorus or mushroom poisoning) that can cause fatty liver changes. Infections can also cause fatty liver, such as hepatitis c & HIV infection.
Various. Though the exact cause is unknown, it is associated with conditions such as alcoholism, diabetes, overweight status and a poor diet.
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