It would be like studying an intensive exercise program — including long runs, calisthenics and strenuous sports — among sedentary volunteers for just six days. The investigators might find that the program made the volunteers sore, tired and weak. However, a six-month trial, allowing adequate time to adapt to the new regimen, would reach the opposite conclusion, revealing the real benefits of physical activity.
Despite their greater difficulties, diet trials receive far less funding than drug trials, especially considering that poor diet is the leading risk factor for premature death. Few big companies stand to profit directly from dietary treatments for chronic diseases. Consequently, typical diet trials must get by on shoestring budgets, rarely exceeding a few hundred thousand dollars, compared with drug trials that may cost several hundred million dollars. Without adequate support, quality inevitably suffers. Diet trials of adequate size, duration and intervention strength rarely get done.
This problem has special relevance now, as the Dietary Guidelines Advisory Committee reviews the science in preparation for new Department of Agriculture recommendations to the public in 2020. Among thousands of scientific articles initially screened, only a small proportion so far have passed strict quality criteria for inclusion in committee deliberations. And ultimately, recommendations to the public can be no stronger than the science on which they rely.
Which doesn’t mean that all nutrition research is unreliable. High-quality observational studies and clinical trials provide strong evidence for the benefits of whole carbohydrates (nonstarchy vegetables, fruits, legumes, minimally processed intact grains) over highly processed, fast-digesting carbohydrates (refined grains, potato products and added sugar). We also know that nuts, olive oil and avocado protect against chronic disease, contrary to dietary recommendations during the low-fat diet era, as embodied by the 1992 Food Guide Pyramid.
We need a sort of Manhattan Project to find definitive answers to the epidemics of diet-related disease. Nutrition research to prevent disease must have the same quality and rigor as pharmaceutical research to treat disease. Building the necessary scientific infrastructure will require sustained investment by government and philanthropic organizations, but the amounts involved would total a fraction of a cent for every dollar spent treating diet-related conditions like obesity, Type 2 diabetes and cardiovascular disease.
Study authors and the media can help by avoiding the tendency to overstate the results of weak research, contributing to public confusion. And the public has a critical role to play, not only demanding government action but also volunteering for diet studies.
No other factor approaches the importance of diet for public health. To reduce the human toll of chronic disease, we must upgrade the quality of nutrition research. The financial investment required will yield huge returns in medical cost savings.