As many of you are now aware, U.S. News and World Reports (USNWR) has just issued their annual ratings of Best Diets for 2014. As per their 2011, 2012 and 2013 evaluations, the DASH diet was rated number one by a panel of nutritional and health “experts,” and The Paleo Diet again emerged last out of 32 diets which were considered. We have previously addressed the USNWR report as it relates to the Paleo Diet in extensive detail in the Original Rebuttal to the USNWR. I have a few additional important points which follow:
I would like to point out a number of crucial flaws in logic along with a total breakdown of the scientific method in these types of artificial, media-generated reports that invalidate any wide sweeping conclusions about diet reached by the popular press, by individual member of the USNWR panel or by USNWR itself.
The 2014 USNWR diet ratings represent nothing more than the subjective rankings of 32 popular diets by a group of professionals, ultimately hand-picked by the editorial infrastructure at USNWR. Notably lacking in the makeup of this panel are academic and medical professionals with a background and publication record in human evolution, ancestral human diets and the application of this diet within a clinical setting.
The USNWR ratings represent a purely subjective appraisal of 32 popular diets and accordingly has little or no objective value from a scientific perspective because of numerous and glaring flaws in the research design of this report. Let me give you an example.
Say you would like to experimentally test three different diets (Diet A, Diet B and Diet C) on a single outcome variable (perhaps, blood pressure) to determine which diet was most effective in lowering blood pressure. Such an experiment would require that you test Diet A to Diet B, Diet A to Diet C and Diet B to Diet C. Scientists then run statistical tests on these three trials (A to B, A to C and B to C) to determine the effectiveness (or lack thereof) of all three diets and all three possible comparisons.
If we would like to test four different diets (Diets A, B, C and D) against one another for their specific effectiveness on blood pressure, it would require 6 individual experiments (A to B; A to C; A to D; B to C; B to D and C to D). As more and more diets are tested against one another, the number of experiments required to evaluate one diet against the next rises exponentially (actually factorially).
To test 32 diets against one another, would require 538 individual experiments and at least 538 statistical comparisons!
These 538 experiments have never been conducted. In fact, very few of the 32 popular diets evaluated by the USNWR panel have ever been examined in the scientific literature or tested against one another statistically. Without objective data, ratings of popular diets by this or any panel of “experts” represent nothing more than pure subjective speculation by the members of the panel. Clearly another “expert” panel with an entirely different makeup could be convened whose dietary ratings may vary entirely from the USNWR panel.
Like it or not this is how science works. Hypotheses must be formulated and statistically tested. If the USNWR panel believes the DASH diet is superior to The Paleo Diet, it must be experimentally tested. You cannot say that one diet is more effective than another diet without testing it statistically with either experimental or epidemiological (population) studies. So, to say that the DASH rates number #1 among all 32 diets for either a single outcome variable (say blood pressure) or multiple outcome variables (weight loss, blood pressure, blood cholesterol levels, ease to follow, satiety, etc. ) is absolute nonsense from a scientific perspective.
I recognize a number of well-known and well published scientists on the USNWR panel. These scientists would be the first to tell you that the USNWR ratings are subjective in nature and not based upon factual comparisons found in the scientific literature testing each of the 32 diets against one another.
In contrast, The Paleo Diet has been frequently examined in the scientific literature and shown to be effective in facilitating weight loss, improving cardiovascular risk factors and satiety while being more nutrient dense for the 13 vitamins and minerals most lacking in the US diet when compared to the USDA Food Plate (formerly the Food Pyramid).
Loren Cordain, Ph.D., Professor Emeritus