Although drugs are routinely subjected to testing by clinical trials before they are approved and recommended, diets typically have very weak evidence behind them even though they likely have a strong influence on health and disease.
"People who choose to eat more fish are more likely to eat heart healthier diets and engage in more physical activity, " and studies testing the benefit of supplements may not be able to completely adjust for differences like these, said Alice Lichtenstein, director of the cardiovascular nutrition lab at Tufts University in Boston.