Medical science has made enormous strides since the release of the first national Dietary Guidelines in 1980, but many would agree that the quality of the American diet appears inversely related to these health gains. We've added years to our lifespan and provided the safest, highest quality foods possible yet, as a nation, the quality of our diet has deteriorated. The Secretaries of Health and Human Services and of Agriculture will soon name the next DGAC to define the science base for the 2010 Guidelines. This is the place to fix the problem. We need to establish the new 2010 Guidelines as worthy of the trust Americans hope to place in them as an authoritative source of information about their food choices.
The Secretaries should consider carefully the critical importance of the selection criteria for Committee members. With obesity at historic levels and childhood obesity a near epidemic with grave long-term consequences for our nation, the need for policy guided by expert scientists is clear. No one could deny that the first six DGACs were composed of prominent medical and nutrition experts. There can be no quarrel with the professional, subject matter qualifications of past DGAC members. It's the paradigm that needs changing.
Committees of subject matter experts produce reports with expert opinion. That sounds better than it really is. In the hierarchy of "evidence-based" medicine, expert opinion is the lowest level of evidence. Rigorous data analysis trumps even well-informed opinion. To sort out public confusion and establish consensus authority, we need to move higher on the evidence-based hierarchy. We must do better for the nation. Evidence-based decision-making focuses less on the experts and more on the evidence. While as good they could be, because past DGACs have not followed the best discipline, their reports cannot claim the mantle of evidence-based reviews. We need to change the DGAC process, not just the people on the Committee.
Using a process like the one developed in the 1980s by the Cochrane Collaboration , inventors of "evidence-based medicine," will allow this new DGAC to take the next step in the process and set the standard and grade the evidence before considering the policy analysis. We need this different expertise on the DGAC in order to make the Guidelines reflect the science and become most relevant to Americans' health.
The federal government endorses an evidence-based approach to health policy and the U.S. Preventive Services Task Force (USPSTF) is the model for how the DGAC could adopt the discipline of evidence-based decision-making. Supported by the HHS Center for Outcomes and Evidence and a contracted Evidence-based Practice Center in Oregon which conducts systematic reviews of the evidence, the USPSF makes its recommendations on the basis of explicit criteria. The USPSTF reviews the evidence, estimates the magnitude of benefits and harms for each intervention, reaches consensus about the net benefit for each intervention, and issues a recommendation - from "A" (strongly recommends) to "I" (insufficient evidence to recommend for or against).
The USPSTF process would be the most appropriate and effective model for the DGAC. An evidence-based review will require an evidence-based process; this requires changing the concept of the DGAC which up until now has been compiling expert opinion instead of conducting an evidence-based review.
In a courtroom, judges rely on subject matter experts: witnesses attest to their observations and "expert witnesses" offer their professional opinion. Judges are not subject matter experts; they are process experts. They know what observations and opinions to admit into evidence. They discipline the process. The DGAC has been acting as an "expert witness" instead of a judge. We need a DGAC composed of "judges" - experts in the process of evidence-based decision-making. We need "judges" who have a proven dedication to dispassionate review of the evidence. And we need their report to reflect their conclusions about the quality of the evidence before the policy conclusions and recommendations.
How often have we heard the anti-salt advocates, the "so-called" experts, refer to the Intersalt study, and in particular the Yanomamo Indians of Brazil. These primitive hunter-gathering tribes are held out by these experts as prime examples of the benefits of low-salt consumption, because they do not experience any age-related increase in blood pressure.
Indeed, one of the main conclusions coming out of the study was that the Intersalt populations with low-sodium intakes had low median blood pressures, a low prevalence of hypertension and no increase in blood pressure with age. Disregarding any other factors, the experts stated that the low levels of hypertension among these tribes was the exclusive result of low-salt consumption.
Such conclusions reflects the dangers of commitment to a single focus approach to science - an approach that almost always manages to manipulate the interpretation of data in order to support a prejudged conclusion. And, not particularly surprising, all the "experts" continue to use the Yanomamo Indians as primary proof that reduced salt consumption results in an absence of hypertension.
Two out of the four low-sodium populations in the Intersalt study - the Yanomamo and Xingu Indians are of Amerindian origin. Both these populations have a complete absence or a very low frequency of the D/D genotype - a genotype that is closely associated with cardiovascular diseases and hypertension.
So, it's not low salt consumption that results in the lack of an age-related rise in blood pressure in the Yanomamo and Xingu Indians, it's their genetic makeup!
Studies in Mexican Americans suggest that diseases such as obesity, diabetes mellitus, cholesterol gall stones, and gall bladder carcinoma are more common in individuals with high Amerindian genetic background (1,2,3). On the other hand, these individuals present low risk for developing cardiovascular disease, in spite of data that show serum triglyceride concentrations to be slightly higher in this population than in Caucasians at any age (4,5). These data suggest that Amerindians are protected against developing cardiovascular diseases due to their genetic background.
An interesting fact is the different prevalence of hypertension in several states of Mexico. Thus, states with a high Amerindian genetic background, such as Puebla, Chiapas, and Oaxaca present a low prevalence of hypertension when compared to the northern states of the country Coahuila, Sonora, and Sinaloa with a low Amerindian genetic background.
These differences explain the low genetic susceptibility for cardiovascular diseases and hypertension in populations with high Amerindian background such as the Yanomamo and Xingu.
How many other myth-interpretations are the "experts" responsible for?
It is hoped the new Dietary Guidelines will not be a product of the four M's, Myth-information, Myth-interpretation, Myth-representation, and Myth-guided policies
1. Hanis, C.L., R.E. Ferrell, S.A. Barton et al., « Diabetes among Mexican Americans in Starr County, Texas," Am. J. Epidemiol, 118, 659-672, (1983). 2. Hanis, C.L., R. Chakraborty, R.E. Ferrell et al., "Individual admixture estimates: Disease associations and individual risk of diabetes and gallbladder disease among Mexican-Americans in Starr County, Texas," Am. J. Phys. Anthropol, 70, 433-441, (1986). 3. Haffner, S.M., A.K. Diehl, M.P Stern et al., "Central adiposity and gallbladder disease in Mexican Americans," Am. J. Epidemiol, 129, 587-595, (1989). 4. Weiss, K.M., R.E. Ferrell, and C.L. Hants, "A New World syndrome of metabolic diseases with a genetic and evolutionary basis," Yearbook Phys. Anthropol, 27, 153-178, (1984). 5. Mitchell, B.D., M.P. Stern, S.M. Haffner et al., "Risk factors for cardiovascular mortality in Mexican Americans and non-Hispanic whites. The San Antonio Heart Study," Am. J. Epidemlol, 131, 423-433, (1990).
