To determine which specific dietary component may account for the blood pressure-lowering effect produced by vegetarian diets, numerous studies have examined individual micronutrients, macronutrients, and fiber. A large majority of cross-cultural and observational studies have shown a significant inverse association of blood pressure with the micronutrients, potassium, calcium, and magnesium, while the evidence linking dietary fiber to lower blood pressure comes primarily from studies on vegetarian and other high fiber diets. However, only a few of numerous clinical trials found that potassium or calcium supplements lower blood pressure. Randomized trials of magnesium supplementation generally have not shown a significant reduction in blood pressure. The few intervention studies of fiber supplements likewise generally have not demonstrated significant lowering of blood pressure. Pooled estimates from meta-analyses of potassium and calcium trials have reported small but significant reductions in systolic (potassium and calcium) and diastolic (potassium) blood pressure. All of these results are compatible with small effects of individual dietary components.