There has been a shift from studying single nutrients to dietary patterns over the last several years. When doing these types of studies, some researchers measure adherence to each of the dietary patterns in their study. Why? 

If participants aren't adhering to the diet, the researchers can step in and help them make the necessary changes. 

They can only compensate participants who adhere to their study diets.

If participants were assigned to eat more of one nutrient and less of another but they didn't, drawing conclusions becomes challenging.