Understanding the environmental determinants of the increase of blood pressure with age (the underlying phenomenon for essential or primary hypertension) has substantially progressed during the past 3 decades (1). Increased understanding of mammalian physiology, animal models of disease, clinical observations, and epidemiologic studies have helped identify lifestyle factors that likely influence blood pressure in humans. Appropriately, randomized, clinical trials have been considered necessary to validate putative causal relationships. By the 1990s, the evidence was sufficiently robust to justify 4 recommendations for preventing and treating hypertension by lifestyle intervention: controlling body weight (or adiposity), reducing dietary salt (sodium chloride), increasing physical activity, and limiting alcohol use to no more than a moderate level (2). The evidence for increasing potassium intake was considered good but somewhat less conclusive than that for these 4 factors. Evidence for other nutritional factors was considered inconclusive. Nevertheless, research continued on potential dietary determinants of blood pressure, especially divalent cations (that is, magnesium and calcium), fiber, and macronutrients (including fats and protein) (3). Our editorial summarizes the results of several studies of protein, with a focus on He and colleagues' randomized trial published in this issue (4).