Nutritional research and policies have been criticized for relying on observational evidence, using self-report diet assessment methods, and supposedly being unable to present a consensus on what constitutes a healthy diet. In particular, it is often asserted that for progress to occur in nutrition science, large, simple trials, which have worked well in evaluating the efficacy of drugs, need to replace most observational research and small trials in nutrition. However, this idea is infeasible, and is unlikely to advance nutritional sciences or improve policies. This article addresses some commonly held and unfounded "myths" surrounding dietary assessments, effect sizes, and confounding, demonstrating how carefully conducted observational studies can provide reliable and reproducible evidence on diet and health. Also, there is a strong consensus among nutritional researchers and practitioners about the basic elements of a healthy diet. To move forward, we should continue to improve study design and diet assessment methodologies, reduce measurement errors, and leverage new technologies. Advances in the field lie in coalescing evidence from multiple study designs, methodologies, and technologies, and translating what we already know into policy and practice, so we can improve diet quality and enhance health in an equitable and sustainable manner across the world.