Complex sentence: Campbell disagreed with its conclusion that increased consumption of animal protein is associated with decreased risk of ischemic heart disease and criticized the homogeneity of the study population and its high-animal-protein diet, and criticized the application of pharmaceutical-style analysis of individual nutrients.
Split into simpler sentences: Campbell disagreed with its conclusion that increased consumption of animal protein is associated with decreased risk of ischemic heart disease and criticized the homogeneity of the study population and its high-animal-protein diet. Campbell further criticized the application of pharmaceutical-style analysis of individual nutrients.