How are we to determine whether dietary interventions do more good than harm to hypertensive patients?

This paper categorizes studies of dietary interventions in hypertensive patients into five categories based on the levels of evidence: level I, randomized trials with low false-positive (alpha) and low false-negative (beta) errors (high power); level II, randomized trials with high false-positive (alpha) and (or) high false-negative (beta) errors (low power); level III, nonrandomized concurrent cohort comparisons between contemporaneous patients who did and did not receive a nutritional intervention; level IV, nonrandomized historical cohort comparisons between current patients who did receive a nutritional intervention and former patients (from the same institution or from the literature) who did not; level V, case series without controls.