How legitimate is the common corporate criticism of the scientific nutrition literature that the credibility of observational studies is questionable? While randomized controlled trials are highly reliable in assessing interventions like drugs, they’re harder to do with diet. Dietary diseases can take decades to develop. People can’t eat placebo food, and it’s difficult to get them to stick to assigned diets, especially for the years it would take to observe effects on hard endpoints like cancer or heart disease. That’s why we have to use observational studies of large numbers of people and th...