Given the following passage  "Nutritionism is the view that excessive reliance on food science and the study of nutrition can lead to poor nutrition and to ill health. It was originally credited to Gyorgy Scrinis, and was popularized by Michael Pollan. Since nutrients are invisible, policy makers rely on nutrition experts to advise on food choices. Because science has an incomplete understanding of how food affects the human body, Pollan argues, nutritionism can be blamed for many of the health problems relating to diet in the Western World today.",  answer the following question. Note that the answer is present within the text.  Question: What makes it hard to evaluate food values?
The answer to this question is:
science has an incomplete understanding of how food affects the human body