BACKGROUND The effects of caffeine on fatty liver induced by high-fat (low-carbohydrate) diets were examined in the presence or absence of alcohol consumption by rats. METHODS For periods ranging from two to twelve weeks, male Long-Evans rats were given alcohol-free or alcohol-containing liquid diets balanced for energy content, but varying in fat and carbohydrate. In addition, several of the groups were given 0.05% caffeine as a constituent of the liquid diet. At the end of the experiments, trunk blood was collected for blood glucose and plasma leptin, epididymal fat pads were weighed, and liver was taken for analysis of glycogen, glucose, and fat. RESULTS Ethanol-containing diets increased liver fat and depleted liver glycogen and glucose as compared to the corresponding ethanol-free diets, but these effects were less severe in rats given high-carbohydrate diets as compared to those maintained on the high-fat diet. The inclusion of 0.05% caffeine in the diet increased the motor activity of animals with access to a running wheel, yet had no protective effect against ethanol-induced depletion of liver glucose and induction of fatty liver. In fact, caffeine appears to exacerbate the effect of ethanol to deplete liver glycogen, decrease epididymal fat pad weight and lower serum leptin. CONCLUSIONS Since liver glycogen stores can be depleted by treatments such as caffeine which do not exacerbate ethanol-related liver fat accumulation, the depletion of liver glycogen following chronic ethanol is not the single causal determinant of the resulting fatty liver. Other aspects of carbohydrate metabolism, including accumulations of endogenous regulatory intermediates or ethanol-derived compounds, might be more directly influenced by chronic alcohol ingestion.