Endothelial dysfunction is an early precursor to atherosclerosis. Lifestyle interventions, including diet, have been shown to affect endothelial function. High-fat diets have been shown to impair endothelial function, and diets such as the Mediterranean diet have been associated with improved endothelial function. This review discusses the effects of diet, dietary supplements such as folic acid, polyphenols, and antioxidant vitamins on endothelial function. We provide a summary of the current data linking diet with endothelial function and explore controversies within this field.