Why Nutrition Is A "Soft Science"

"Of course, this type of clinical trial isn't suited to most nutritional research. Simply altering intake of one food or another doesn't take into account the rest of the diet, and again, accurate quantities are hard to come by. A well-controlled study of intake on a metabolic ward (a hospital or clinic where participants in a study might live or get all their foods), for example, involves actually weighing the foods, whose composition has been scientifically determined, given to participants. Any foods a person doesn't eat are weighed again, and the amount actually consumed can be determined by the difference. Obviously, this isn't conducive to learning what free-living people really eat.

"Unless and until we develop solid means of determining what people really eat, I'm afraid we're bound to continue to find contradictions in nutrition research."

Reliability of Nutrition Research Questioned