The science of nutrition is a disaster. For a variety of very good reasons it is nearly impossible to perform high quality, long term randomized controlled trials to provide satisfactory answers to most of the pressing questions of the day.
But many experts are convinced they do know the answer to many of these questions. The problem, of course, is that these experts hardly ever agree with each other.
You wouldn’t know about all the confusion by reading the recently published updated US Dietary Guidelines (USDG). It appears to represent the consensus of a significant portion of the nutrition establishment. But, as if to highlight the complete lack of a genuine consensus, these guidelines are coming under fierce attacks from other, equally distinguished experts representing a wide range of differing views. There is no consensus among these critics regarding the specific details of how the guidelines went wrong or how they should be fixed. But there is widespread agreement that the guidelines are seriously deficient in that they lack strong scientific support.
The most recent assault on the USDG is contained in a commentary by Steve Nissen (Cleveland Clinic) in Annals of Internal Medicine. Nissen writes that the lack of genuine evidence “has left dietary advice to cult-like advocates, often with opposite recommendations. One group advises virtually complete elimination of carbohydrates from the diet, whereas others promote a virtually fat-free diet.” Nissen concludes that “it is time to transition from the current evidence-free zone to an era where dietary recommendations are based on the same quality evidence that we demand in other fields of medicine.”
Nissen’s article focuses largely on the recommendations about dietary fat and cholesterol. Although early in 2015 a preliminary draft of the guideline stated that “cholesterol is not a nutrient of concern for over-consumption” Nissen writes that “incredibly, in the final 2015 report, this statement has been removed, instead suggesting that ‘individuals should eat as little dietary cholesterol as possible.’ Which version should we believe? How can the same committee arrive at diametrically opposite conclusions?”
Bad dietary advice has serious consequences. Nissen reminds readers that as a result of previous guidelines and campaigns that demonized fat, Americans “binged on carbohydrates and became increasingly obese. Type 2 diabetes grew into an epidemic that is now threatening to reverse decades of progress in reducing coronary heart disease incidence.”
Nissen appears to side with critics who oppose the continued recommendations to reduce dietary cholesterol and saturated fat. “The best available evidence does not clearly support the widely held belief that Americans should limit saturated fat and cholesterol in the diet,” he writes.
A leading figure in the fight against the guidelines has been Nina Teicholz, author of The Big Fat Surprise and a controversial BMJ investigation presenting a very detailed case against the guidelines. Teicholz says that Nissen’s piece “confirms much of what” she wrote in the BMJ. “These ideas are challenging to the nutrition establishment, which has long defended a diet low in fat and saturated fat, but the science on those recommendations has never been strong and is now being challenged by a growing number of researchers.”
The Circular Firing Squad of Nutrition Experts
The sheer number and variety of attacks against the new guidelines is bewildering, since no two critics seem able to reach agreement or disagreement on most major points.
In an article labelled an “authoritative review” by the editors of Circulation, one expert, Dariush Mozaffarian (Tufts University), points out the weak scientific evidence underlying much of the new guidelines, but then proceeds to offer his own personal interpretation that in many cases closely mirrors the USDG. Mozaffarian, who is himself a well-regarded member of the nutrition establishment, rejects the scientific basis for the guideline recommendations that saturated fat be restricted to 10% of all calories in the diet and that favor vegetable oil over butter. On the other hand, Mozaffarian appears to give broad support to the low sodium position adopted by the committee, though this has also provoked strong scientific criticism.
Another frontal assault on the guidelines appears in the Mayo Clinic Proceedings. The authors write that “in the 2015 DGAC report, the distinction between correlation and causation is either ignored or dismissed. For example, the words association, associated, and relationship are used more than 900 times in the 571-page DGAC text, whereas the words causal and causality are used fewer than 30 times and not once to describe an actual causal diet-health relationship.” They conclude that the guidelines committee “generates national public health policy recommendations via mere statistical associations from physiologically implausible data while ignoring established causal factors for the development of chronic noncommunicable diseases.”
However, it is important to note that these authors have themselves been the target for intense attacks over the past year. Two of the authors, Edward Archer (University of Alabama at Birmingham) and Carl Lavie (Ochsner Clinic), were criticized for receiving research funds from Coca Cola.
Another often-quoted obesity expert, David Katz, calls the guidelines a “national embarrassment,” but for very different reasons. He doesn’t appear to object to the science behind the guidelines but, instead, “the political adulterations of the excellent work of scientists.” Katz endorses the committee’s recommendations regarding dietary fats and cholesterol. In fact, if I understand him correctly he believes the committee, subjected to pressure from industry and other sources, didn’t go far enough.
You may also want to read: Why Guidelines Are Bad For Science