Dietary factors might affect the risk of atrial fibrillation (AF), but available studies have provided inconsistent results. A review of published observational studies and randomized trials identified 4 dietary exposures that had been investigated regarding AF risk: alcohol, fish-derived n-3 polyunsaturated fatty acids, caffeine, and ascorbic acid. Though studies were highly heterogeneous in their design and results, they showed a consistently increased risk of AF in heavy alcohol drinkers, but no risk associated with moderate alcohol intake. High coffee intake was not clearly associated with an increased risk of AF, and a potential U-shaped association (lower AF risk in moderate drinkers) could exist. High intake of fish-derived n-3 polyunsaturated fatty acids from diet or supplements might prevent AF episodes following cardiovascular events, but no consistent evidence supports an effect in primary prevention. Additional large, well-conducted randomized experiments are necessary to address the role of diet in AF prevention. (Circ J 2010; 74: 2029-2038)