by Marion Nestle
Apr 27 2016

The fuss over previously unpublished data from the Minnesota Heart Study

A couple of weeks ago, I mentioned several new studies that elicited much media attention.  I am now getting around to them.

Let’s start with the article in the BMJ about newly discovered data from the Minnesota Heart Study purportedly casting doubt on the risks of saturated fat (here’s what the Washington Post said about it).

The BMJ article concluded:

Findings from the Minnesota Coronary Experiment add to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid.

I’ve been at this game long enough to guess that any statement suggesting that everything you thought you knew about nutrition is wrong ought to raise red flags and call for more than the usual degree of skepticism.

Here are some sensible and, yes, skeptical comments about this study:

From Julia Belluz of Vox

But there were a few major problems with the research. The study involved men and women of an average age of 52 who had been admitted to a nursing home and six state mental health hospitals because they were sick. The researchers who conducted the meta-analysis note the “results are not necessarily generalizable to populations without mental illnesses or living outside nursing homes.”

Another issue: The study followed 9,423 women and men, but only a quarter of the participants followed the diets for more than a year. Altering one’s diet for a short period of time — especially in old age — would not necessarily affect one’s long-term health risks….

…Some of the biggest controversies surround saturated fats. Scientists disagree about the extent to which saturated fats contribute to important health outcomes like heart disease, stroke, and cancer. The available research does suggest, however, that there are health benefits from replacing saturated fats with unsaturated fats in the diet, and that eating lots of nutrient-poor carbs (like sugary cereals, soda, and white bread) instead of fat is a bad idea.

From David Katz, to whom I am often grateful for taking on such things, writes that this study

tested something that nobody expert in nutrition is recommending: an extremely high dose of omega-6, linoleic acid…we already got the memo that this is a dubious proposition.

With all due respect to the BMJ authors, I personally found it a bit odd that they stated the following: “A key component of dietary guidelines has long been to replace saturated fat with oils rich in linoleic acid…” The current Dietary Guidelines for Americans, let alone the far better 2015 Dietary Guidelines Advisory Committee Report, make no such recommendation. Searching for any mention of linoleic acid, I found it only in the appendices in the context of descriptions and definitions, not in any of the actionable guidance. While the current Dietary Guidelines do recommend limiting saturated fat intake, the replacement encouraged is a balance of healthful oils, such as olive, and the fats found natively in, as noted, nuts, seeds, avocado, and fish.

From Martijn Katan, the Dutch lipid biochemist who did the original work demonstrating the cholesterol-raising effects of trans fats, writes in an e-mail:

I have not had time to study the BMJ article on the Minnesota Heart Study in detail. However, some of my colleagues did, and I think that their conclusions are correct:

  1. The randomized trial itself showed no effect on disease or death
  2. This was to be expected because most subjects were on the diet for less than 1 year. This was due to the change in regime for psychiatric patients that took place during that period, which essentially caused the trial to fail. Lowering cholesterol by 14% for one year does not noticably affect CVD risk.
  3. The relation of a larger fall in cholesterol with a larger risk of mortality did not emerge from the randomized study; subjects were not randomized to various levels of cholesterol lowering. It is an observational association. The question than arises which causes which. Various occult diseases, notably cancer, cause cholesterol to fall as the disease progresses. This also explains the association seen in observational studies between low cholesterol and cancer. That observation led me to think up in 1985 the technique now known as ‘Mendelian Randomization’ [1]. Application of that technique showed that the association of low cholesterol and cancer is indeed spurious [2].

The only new thing about the present study is that they revived the long disproved hypothesis that lowering cholesterol causes various diseases. Hundreds of thousands of patients in statin trials have proven this wrong….

[1] Katan, M.B., 1986. Apolipoprotein E isoforms, serum cholesterol, and cancer. Lancet 1, 507–8.

[2] Trompet, S.,et al ., 2009. Apolipoprotein E genotype, plasma cholesterol, and cancer: a Mendelian randomization study. Am J Epidemiol 170, 1415–21.

My bottom line on this one

It confirms the value of basic dietary advice: Eat a variety of relatively unprocessed foods, mostly plants (fruits, vegetables, grains, beans, nuts), balance calories, and enjoy what you eat!

Do this and food fatty acids will balance out too and you won’t need to give them another thought.

The moral

Whenever you read a headline suggesting that everything you know about nutrition is wrong, roll your eyes, eat something delicious, and wait for confirming studies to come along before deciding to ignore that basic advice.

  • Stephan Guyenet, PhD

    Hi Dr. Nestle,

    Respectfully, I think there are some important points these commentators left out:

    -This was one of only two double-blind fat modification studies with hard endpoints ever conducted (VA study was the other one).

    -You are aware of the mounting concerns over publication bias. We know that it can gravely distort the scientific record, often in favor of popular hypotheses. This paper was an effort to correct that.

    -While it’s true that most of the subjects didn’t remain in the study past one year, and yes that does substantially weaken the result, they did maintain the intervention in a portion of the cohort to 4.3 years, which is consistent with other fat modification RCTs that are commonly cited. Since the study was enormous, the remaining cohort was still substantial.

    -Many public health authorities, including the Harvard School of Public Health, recommended eating high-LA, low-n3 oils like corn oil for a long time. It’s disingenuous for folks to claim they knew the ineffectiveness of this all along, when they know it partially because of Ramsden’s work, and it is not entirely compatible with their previous position. Ramsden’s work has contributed to a growing awareness of the fact that high-LA oils without n3 is not necessarily going to reduce CVD risk, despite a decline in circulating cholesterol. This is a reversal of a prevailing hypothesis in the nutrition world, and as such should not be denigrated (in my opinion).

    -The paper did not claim to reverse everything we know about nutrition. Perhaps that’s how it was spun in the media, but that’s not what the paper itself said. Instead, what they did was the most rigorous thing possible: they took the new data and used them to update a meta-analysis of fat modification studies. The reality is that the addition of the new study didn’t have much impact on their previous conclusions– but there was no way to know this in advance– the study had to be done. The conclusion remains that high-LA oils without additional n3 do not reduce CVD endpoint risk, which again is a reversal of a previously popular hypothesis.

    In sum, the negative attitude that has been directed toward this study by nutrition authorities is unwarranted, particularly since most of them haven’t read the paper. Yes, it has major limitations (most notably the high dropout rate), but why dismiss it wholesale rather than recognizing the elements that are informative? And why not recognize its value in the larger narratives of fighting publication bias and supporting a more nuanced understanding of dietary fatty acids? It’s really difficult for me to understand this attitude.

  • FromPA

    Not to mention that this is a cornerstone of the whole “let’s eat unnatural seed oils” dietary guidelines. And it does not support that. Furthermore, Keys was involved and appeared to basically hide this information, since it did not agree with his pet theory (which became part of the guidelines), which was that seed oils were good and saturated fat was bad.

    Let’s call this study for what it is: it’s junk. It’s always been junk. And yet they used this to push ALL AMERICANS to eat seed oils. That’s is what is wrong with nutritional “science” — it’s not “science”, it’s “whoever happens to be in charge and can push whatever agenda they have”.

    It’s time we as Americans took back our nutrition from people pushing agendas. If it’s not supported by actual randomized controlled trials with enough people and for long enough to determine an outcome, STOP GIVING GUIDANCE. Just STOP.

    Women’s Health Initiative: A massive study of 59000 women split into two groups. The group under test ate more fruits and vegetables, less red meat, less fat, less saturated fat, fewer calories, everything you are supposed to do according to the guidelines, and at the end of 8 years and half a BILLION dollars, there was no difference between the group under test and the control group in heart disease, cancer, you name it. Given this, why do the guidelines still advocate low fat and reduced red meat? STOP GIVING GUIDANCE. America would be healthier.

  • George

    Dr Katz cannot have read the current dietary guidelines, or perhaps he does not have access to Google, because corn oil is listed as a healthy fat source in the 2016 press release.
    http://www.fns.usda.gov/pressrelease/2016/000516

    It is special pleading to evoke the concept of “occult disease” lowering cholesterol and causing death, when higher intake of omega 6 is likely to be a factor in such occult diseases. For example, if persons hospitalised for alcoholism were randomised to linoleic acid this is likely to have increased the progression of alcoholic liver disease, a condition likely to have lowered cholesterol, and for which saturated fats play a protective role.
    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4808795/

    This harm can no doubt be attributed to alcohol, yet this still does not mean that recommending polyunsaturated oil is safe at a population level, unless it comes with clear warnings to avoid such oil when drinking alcohol.

    I am surprised that the brains trust you relied on for analysis of this important debate comprises at least one person who did not read the paper, the egregious Dr Katz, and one of the scientists from Vox.
    This is much too important a question (does the effect of fat on cholesterol have any influence on the risk of disease) to be treated so lightly.

    A novel food product was recommended to the world as the result of a politicized process – surely the epitome of Food Politics.
    Yet when tested for efficacy or safety, it had failed every test; it did not prevent the disease it was supposed to prevent, or any other disease, and it caused adverse effects in the population.
    This is the real story here.

  • George

    Further to the claim that Dr Katz makes, that the Dietary Guidelines do not mention linoleic acid – of course, the guidelines are aimed at the general public and will no more mention linoleic acid than they will mention l-leucine.
    However, the guidelines were composed following the composition of this background report, which summarises the research used by the committee to compose the guidelines.
    http://health.gov/dietaryguidelines/2015-scientific-report/PDFs/Scientific-Report-of-the-2015-Dietary-Guidelines-Advisory-Committee.pdf
    There are mentions of linoleic acid and n-6 fatty acids in this report, of which the most significant is a summary of the 2014 meta-analysis of prospective cohort studies by Farvid et al.
    This summary mentions the reduction in coronary events and deaths associated with a 5% increase in LA in an open ended fashion, i.e. there is no discussion anywhere in the report of a possible upper limit.
    The association of LA with CHD in Farvid et al was not controlled for intake of omega-3 fats; yet the Ramsden et al 2013 meta-analysis was available.
    There is no discussion of a possible upper limit for intake of LA or total PUFA in the report. The failure to cite Ramsden 2013, the only meta-analysis of RCTs to compare oils that supply omega-3 with oils that do not, means that evidence about the safety of high-linoleic acid diets was excluded from consideration.
    In 2013 the AHA, a body which informs the DGAC, released a statement stating in part that

    “The American Heart Association continues to recommend limiting saturated fats to less than seven percent of total calories consumed and supports eating between five to ten percent of total calories from Omega-6 PUFAs”
    (This is similar to the WHO recommendation of 6-11% LA).

    The 2015-2020 guidelines seem to have created a new food category, “Oils”, which Americans are not eating enough of; this category includes corn oil by name.
    http://health.gov/dietaryguidelines/2015/guidelines/chapter-2/a-closer-look-at-current-intakes-and-recommended-shifts/

    What do overseas authorities say?

    Upon request of the European Commission, the European Food Safety Authority (EFSA) proposed adequate intakes (AI) for the essential fatty acids LA and ALA, as well as the long-chain omega-3 fatty acids EPA and DHA (62). EFSA recommends an LA intake of 4% of total energy and an ALA intake of 0.5% of total energy; an AI of 250 mg/day is recommended for EPA plus DHA.

    The International Society for the Study of Fatty Acids and Lipids (ISSFAL) recommends for healthy adults an LA intake of 2% energy, ALA intake of 0.7% energy, and a minimum of 500 mg/day of EPA plus DHA for cardiovascular health.

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  • Philip Chu
  • kylemeister

    I read just as far as the bit saying that Keys never explained why he chose the countries he did except for one throwaway line. I don’t believe that is the case. From the various things I’ve read over the past couple of years or so rebutting that sort of claim, here is one which Dr. Nestle linked to in her blog post of April 28.
    http://www.thenutritionwonk.com/#!Ancel-Keys-and-the-Seven-Country-Study-A-Response-to-The-Sugar-Conspiracy/cmbz/570ed1910cf20b4e25a4d9f2

    One of the things that stuck in my memory about Anthony Colpo is that he apparently pretended that a trial of the Dean Ornish program was a failure because the results showed no significant differences between the intervention and control groups — without mentioning that the control group consisted of people who received heart surgery.
    http://plantpositive.com/42-you-win-anthony-colpo