What diet works best to prevent obesity, diabetes, cardiovascular disease, cancer and Alzheimer’s? This question has gained special significance, with increasing attention to the epidemics of diet-related chronic diseases. However, answers remain elusive.
A new paper in The BMJ, British Medical Journal by DBEI and CHIBE faculty member Mary E. Putt, PhD, ScD, and Harvard researchers David S. Ludwig MD, PhD and Walter C. Willett, MD, DrPH finds that that the problem may be rooted in poorly designed nutrition research.
The authors reviewed trials utilizing the 2-by-2 cross-over design, an increasingly common method in the field. They found that most of these trials were at risk of substantial bias because the wash-out periods were too short to eliminate carry-over effects.
In addition, although short-term dietary trials are less expensive and logistically simpler, the results of these trials should not be extrapolated to long-term dietary impacts on chronic disease. As the authors conclude, short-term trials are no substitute for definitive long-term trials.
In an associated opinion piece in STAT News, Professors Putt and Ludwig argue that short-term dietary trials – such as those in the $170M Nutrition for Precision Health initiative of the NIH – not only waste money, but could also distort the evidence base upon which future national nutrition guidelines are based.