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Evidence for the American Heart Association's diet is....a single clinical trial
Scientific review showing slim evidence is then deep-sixed
The American Heart Association (AHA) considers its diet the ‘gold standard’ for fighting heart disease. But exactly how much gold lies in the vault to back up that ideal? This question came up in my last column, in which I examined a recent AHA “Scientific Statement” that ranked popular diets according to how well each one matched up with the AHA’s own diet plan. This system works only if AHA nutrition advice is, in fact, the most effective and most evidence-based. The last time the AHA published a formal “Guideline” on nutrition, in 2019,I remember witnessing the scientific evidence review for the guideline vanish in real time from the internet. I contacted various AHA officials and could not get any satisfactory answers. Why would the AHA deep-six its own evidence?
The AHA has long been the leading group in the fight against heart disease, going back to its founding in 1948. In 1955, after the AHA was credited for helping President Dwight Eisenhower recover from a heart attack, the group enjoyed staunch White House support for decades to come. Presidents launched nation-wide AHA fundraisers from the White House and handed out AHA awards direct from the Oval Office, while their wives served as Honorary Chairmen.The AHA’s extraordinary relationship with Presidential power continued through the Nixon era. Yet even as these prestigious connections waned, the group retained its influence with the National Institutes of Health and federal agencies in charge of the nation’s top nutrition policy, the Dietary Guidelines for Americans. For 40-plus years, these government guidelines have followed in lockstep with AHA dietary advice. Thus, with regard to nutrition guidelines, there’s arguably never been a group more influential than the AHA.
Here are the group’s current recommendations, from its website, on what to eat to avoid heart disease.
Note that this advice reflects some major reversals since the AHA’s original dietary guidelines, in 1961.
First, the low-fat diet is gone. This happened quietly, in the mid-2000s, with the words “low-fat” simply disappearing from the AHA’s website. Confusingly, however, the group still considers you better off eating low-fat potato chips over the regular version. This would seem to reflect the principles of a low-fat diet, but the AHA will no longer say that overtly. (By contrast, lean meat and low-fat dairy continue to be encouraged due to their lower saturated-fat content, not total fat.)
Second, the AHA dropped its longtime cap on dietary cholesterol. This was historically set at 300 mg per day and was the reason that for decades, we avoided eggs. You probably don’t know the cholesterol limit has now been vamoosed, since the AHA made no effort to communicate this major policy reversal to the public. Still, according to the AHA’s own 2013 evidence review (p.18), there is “insufficient evidence” to tell people to reduce their dietary cholesterol in order to fight heart disease. (“Insufficient evidence” was also the conclusion of two scientific reviews by the government for its Dietary Guidelines, in 2015 and 2020.) From the AHA paper:
Thus, although the AHA itself hasn’t adjusted to this new cholesterol reality by adding eggs to its recommended food list, you can certainly add a dozen-plus to yours.
What about the rest of the AHA diet? The group’s 2019 evidence review—which is, again, its most recent and was undertaken together with the American College of Cardiology (ACC)—examined the evidence available for each piece of dietary advice, with results shown in the table below. Only recommendation #1, it turns out, was found to be supported by “strong” evidence, as represented by the green box and the letter “I.”
(ASCVD means atherosclerotic cardiovascular disease or, basically, heart disease.)
The yellow-boxed “IIa” recommendations are supported only by “moderate” evidence. Surprisingly, these include even the longstanding alarm about saturated fat.
What do “strong” vs. “moderate” even mean? Roughly speaking, these are grades assigned to the overall quality and quantity of evidence. The AHA/ACC explain how these grades determine how much a recommendation can (or cannot) be urged upon the public. Only “strong” evidence can use language of certainty for the general population.
Some public health groups in recent years have become more assertive about dispensing advice to the public despite being apparently unhinged from the quality of the underlying evidence. The AHA turns out to be no different. As one can see on the AHA’s own website (above), the group firmly recommends to the entire adult population a list of nutrition tips, despite quite a few of them being supported by only “moderate” evidence. These recommendations are a violation of the group’s own standards on guidelines.
Yet perhaps we shouldn’t be surprised. A 2019 review in the Journal of the American Heart Association found that only 8.5% of AHA guidelines were backed by “strong” evidence, down from 11% in 2009.
Key recommendations by the AHA/ACC got middling grades, because the evidence was not of high quality. “Quality” refers to the quantity of rigorous studies (clinical trials) and meta-analyses of those studies that support a piece of advice. In the first illustration above, you can see in the blue boxes that the AHA recommendations are supported by only “B-R” or “B-NR” levels of evidence (LOE). This means that none of the AHA recommendations are supported by “high-quality” evidence.
(“RCT” means randomized, controlled clinical trial, which is the highest-quality trial.)
In sum, only a single part of the AHA/ACC diet, its ‘dietary pattern’ of fruits, veg, legumes, nuts, whole grains, and fish, is supported by “strong” evidence. And even that evidence was of only moderate quality. The rest of the AHA/ACC diet doesn’t even meet the AHA’s own standards for population-wide recommendations.
But let’s just pause here to observe that not a single news organization or even the medical press, to my knowledge, published an article questioning the strength or quality of this evidence when the AHA/ACC guideline came out in 2019, even though all these helpful graphics were in the paper for any reporter to see. Every article I can find trumpets the AHA/ACC ‘lifestyle guidelines’ as the unassailable truth. This tells you that health and nutrition reporters are either asleep at the wheel or too afraid to challenge conventional wisdom. Either way, it’s a sobering reality.
AHA buries its own evidence review
I was impressed, actually, that the AHA/ACC initially set out on the high road when launching their scientific review process for the Guideline—but then clearly fell off a cliff when the results turned out so squarely not in their favor.
The AHA/ACC began with a rigorous ‘systematic evidence review,’ outsourced to the Pacific Northwest Evidence-based Practice Center (EPC) at Oregon Health and Science University. Systematic reviews when conducted according to internationally recognized standards, as EPC apparently follows, are the best tool we have to try to ensure that a body of scientific literature is evaluated in a way that is objective, transparent, and reproducible—all essential for good science.
When the AHA/ACC first released their Guideline, the paper linked to the review on EPC’s website. I remember poring over the results and noting, to my surprise, that a single trial was cited to justify the AHA/ACC’s ‘dietary pattern.’ That trial, called PREDIMED, was a test of the Mediterranean diet, conducted in Spain.
A single trial, as we’ve seen, is insufficient for granting a rating of “strong” to a body of evidence, according to not just the AHA but the vast majority of guidelines standards. Also, this trial was published in 2013, so what was the evidence for the AHA diet for the 52 years before then?
PREDIMED is also problematic, because although it tested a diet that does resemble the AHA/ACC advice in some ways, by including more fruits, vegetables, nuts, legumes, and fish (plus shellfish), it did not reduce saturated fat, red meat, or emphasize whole grains (In fact, subjects were advised to eat 60 grams/day of whole grains vs. altogether 110 grams of refined cereals & potatoes, plus pastries, cakes or sweets).Further, PREDIMED recommended copious amounts of olive oil, which is not at all the same as vegetable oil, per the AHA/ACC diet (olive oil is a monounsaturated fat, whereas vegetable oils are polyunsaturated). Overall, PREDIMED was unlike the AHA/ACC advice in important aspects which very well could have influenced the outcomes.
Worse, PREDIMED was actually retracted in 2018 due to serious protocol deviations including questions about whether it was properly randomized. The study was republished, yet scientists including Stanford’s world-famous evidence-based medicine expert John Ioannidis expressed strong lingering concerns about PREDIMED’s basic scientific rigor.
In any case, the fact of having only a single trial to support the AHA/ACC’s main dietary advice was presumably embarrassing, because the whole review disappeared from the EPC website, and the AHA/ACC then “corrected” its paper to erase even a mention of EPC’s name.
I can’t find the systematic review anywhere. What’s missing are a detailed methodology with specific protocols, lists of studies that were included/excluded, and crucially, the studies deemed supportive for each piece of dietary advice. The AHA put out “Supplemental Materials” (see below), but these do not appear to include any of the specifics I mention. Responding to a query I sent in 2019, an AHA rep told me that the methodology is explained in the main paper (section 1.1), but this is just a generalized description of the fact that a methodology was followed. It’s a little like a recipe for fruitcake saying, ‘A recipe for fruitcake, in all its proper details, was followed.’ Trust the fruitcake makers!
So our conclusion is, sadly, that the 2019 ACC/AHA Lifestyle Guideline, which (again) is the last time these two well-respected groups engaged in a serious review of the scientific literature on diet and health, came up with extremely meagre results. This is not at all what one might expect from the AHA, a 75-year-old organization that has been dispensing dietary advice for more than 60 years now. The moral of the story is that if you’re following this group’s advice, dedicating yourself to a diet of fruits, whole grains, nuts, and fish while restricting saturated fat and red meat, you are resting your hopes on a single, once-retracted medical trial that didn’t even test the diet you’re following. Diet-wise, you’re wandering in the dark.
If you’re seeking some answers, here’s a clue: As I was writing this post, results were published from a RCT comparing DASH to Keto. DASH is a reduced sodium diet designed to lower blood pressure that’s long been favored by the AHA. In fact just last month, the AHA rated it the #1 best diet for heart disease, while ranking keto the worst. However, in this trial of 94 adults with obesity/overweight, pre diabetes/type 2 diabetes, or hypertension, here were the results after 4 months:
What you might conclude from this trial along with this entire post is that if the AHA/DASH dietary advice are the gold standard, then hopefully we are living in early 1933, just before its demise.
Sources and notes:
2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines.
Lists of studies (simply listed, without information about how studies were graded to support each recommendation.)
Literature search: Broken link? Doesn’t work for me. Let me know if its’ fixed.
Authors conflicts of interest statement (Note this list only includes the “Writing Committee” and not the conflicts of interest of the 17 members of the ACC/AHA Task Force who also participated in the review process.)
Other web materials, not relevant to the evidence review
Earlier published versions of the Guideline:
Sept. 10, 2019 “version of record” (No mention of EFP Oregon review)
March 17, 2019 first version (Mentions EFP Oregon review)
What remains of the evidence review is a narrative write-up of the review (pp. 18-19 of the Guideline paper). Here, we can see that PREDIMED is the sole clinical trial mentioned. Pictured here is the entire section explaining the evidence for the AHA/ACC dietary pattern.
Note: observational studies are a weak form of evidence that can show associations (‘X is linked to Y’) but cannot demonstrate cause-and-effect relationships (‘X causes Y’). Only clinical trial data can show an intervention (e.g., a diet or pill) causes an outcome, such as obesity or heart disease.
Also note in the above screenshot that PREDIMED was found mainly to reduce stroke, not heart attacks or other cardiovascular events, and did not show a reduction in mortality.
As always, please let me know of any errors you spot, and I will promptly correct.
Note: Since 2019, there’s been a subsequent, 2021 AHA “Scientific Statement” on diet, but this was not a formal AHA “Guideline” paper and as such, was not supported by a formal systematic review of the science. Studies are instead cited in an ad hoc, non-systematic manner.
Moore, William W., Fighting for Life: A History of the American Heart Association 1911-1975, American Heart Association, 1983.
Teicholz, N. The Big Fat Surprise, Simon & Schuster: New York, NY, 2014., pp. 69-70.