A Fresh Look at Problem Areas in Research Methodology in Nutrition.

This paper makes a critical evaluation of several of the research methods used to investigate the relationship between diet, health, and disease. The two widely used methods are randomized controlled trials (RCTs) and prospective cohort studies. RCTs are widely viewed as being more reliable than cohort studies and for that reason are placed higher in the research hierarchy. However, RCTs have inherent flaws and, consequently, they may generate findings that are less reliable than those from cohort studies. The text presents a discussion of the errors that may occur as a result of confounding. This refers to the correlation of the exposure and the outcome with other variables and can mask the true association or produce false associations. Another source of error is reverse causation, which is most commonly associated with cross-sectional studies. These studies do not allow researchers to determine the temporal sequence of lifestyle and other inputs together with health-related outcomes. As a result, it may be unclear which is cause and which is effect. This may also occur with cohort studies and can be illustrated by the inverse association between alcohol intake and coronary heart disease. Mechanistic research refers to the investigation of the intricate details of body functioning in health and disease and this research strategy is widely used in biomedical science. The evidence presented here makes the case that most of our information of practical value in the field of nutrition and disease has come from epidemiological research, including RCTs, whereas mechanistic research has been of minor value.