Flaming Grill

A Red Meat Issue Flames Up

“I am outraged and bewildered,” says Christopher Gardner. The line forms back there, Professor Gardner. Five – yes, five – papers in the Annals of Internal Medicine today are whipping up a flaming hot controversy about nutrition guidance broadly and red meat specifically. The bottom line from all these papers? Maybe we need to admit that the evidence for harm to health from red meat is not so hard and fast as some people like to think. Using GRADE criteria, the certainty about the effects of red meat on health is low. Thus, recommendations to eat less red meat for better health are weak.

In other words, there are indeed different and valid ways to look at the issue of red meat in the diet.

Is Nutrition Advice Special?

Harvard’s Frank Hu doesn’t like applying GRADE standards to nutrition advice. “It’s really problematic and inappropriate to use GRADE to evaluate nutrition studies,” he says. One big problem he has with the GRADE system is that it takes randomized, controlled studies to be the gold standard of evidence. Observational data provides weaker evidence. Such thinking is OK for evaluating drugs. But he wrote in 2015 that the standard should be different for nutritional epidemiology:

Some researchers consider RCTs as the be-all and end-all of causal inference. This sentiment may be appropriate in the pharmaceutical industry, but the drug trial paradigm cannot be readily translated for use in the nutritional sciences.

However, it’s worth saying that standards for scientific rigor were not invented by the pharmaceutical industry. The lead on one of these five papers, Bradley Johnston, explains:

Regarding the reaction among some in the nutrition research community … we are sympathetic to the discomfort of acknowledging the low-quality evidence in one’s field. It seems to us, however, that pretending that the rules of evidence differ across fields because the feasibility of definitive studies is not possible in one’s particular field is a poor solution to the problem. We believe it is important to apply common standards for assessing the certainty of evidence across health-care fields.

So What Are We to Think About Red Meat?

The evidence to say that we’re eating more red meat than we should for our own health is weak. However, we do have other reasons to believe that eating less red meat would be a good thing. Red meat is pretty hard on this planet we share. A little red meat probably won’t kill you. But too much of it might indirectly contribute to killing lots of people through climate change.

Regardless of the those facts, opinions and feelings will drive behavior. As one of these five papers point out, some people are really attached to the red meat in their diets. Others have strong passions for avoiding it. No surprises there.

The Need for Objectivity

It’s not easy to be objective about nutrition, but it’s worth a try. We’ve had enough of outrage. Dennis Bier explained this to the New York Times: “The rules of scientific proof are the same for physics as for nutrition.” Nutrition scientists who beg to differ say that these publications will undermine public confidence in their field. Walter Willett says “people will throw up their hands and say nutritional science doesn’t know what it’s talking about.”

Perhaps, though, Willett and others should consider this. Overstating your case is a sure way to undercut your credibility.

Click here, here, here, here, and here for these five papers. For further reporting, click here, here, here, and here.

Flaming Grill, photograph © Ginny / flickr

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October 1, 2019

4 Responses to “A Red Meat Issue Flames Up”

  1. October 01, 2019 at 6:37 am, Al Lewis said:

    If indeed some particular item in our diet had significant harms (trans fats, sugar), we would know about it by now. A good rule of thumb in epidemiology is the greater the effect, the smaller the sample size needed to show it. it didn’t take long to show that smoking caused lung cancer. And the study showing that very high blood pressure caused strokes needed only a couple hundred participants.

    I don’t know who is right here. I can, however, infer from the messiness and lack of proof one way or the other that whatever the risks or benefits of more or less red meat, they are a small factor in the overall scheme of health and longevity.

  2. October 01, 2019 at 7:35 am, Mary-Jo said:

    Invalidating nutritional observational studies to enable headline statements that eating less red and processed meat was bad advice/no need to eat less red and processed meat, is irresponsible. Yes, a causal link between red/processed meat consumption and poor cardiovascular health and certain cancers cannot be stated at all. But, we cannot ignore certain health outcomes in very large numbers of people eating red/processed meats or not. In nutrition, both types of studies have their value and it’s not helpful to glorify RCTs over observational.

  3. October 01, 2019 at 11:09 am, Allen Browne said:

    Wow! Interesting morning.

    Thanks.

    Allen

  4. October 01, 2019 at 11:47 pm, David Brown said:

    In truth, experimental evidence furnishes the most reliable information about the connection between food intake and disease. Thus far, most experimental evidence favors a treatment approach. For example, there is a lot of excitement about the therapeutic benefits associated with fish oil supplements. The aim, of course, is to alleviate problems stemming from excessive linoleic acid and arachidonic acid intake. To cure the problem, however, requires reduced intake of omega-6s. Excerpt: Combining reduction of the intake of AA with enhancement of the intake of oleic acid will, moreover, also be a better strategy for reducing the total extent of in vivo lipid peroxidation, rather than adding more EPA (with 5 double bonds) and DHA (with 6 double bonds) to a diet already over-abundant in arachidonic acid and linoleic acid. A reduction of the dietary ratio of total polyunsaturated fatty acids to oleic acid will not only make plasma lipoproteins less vulnerable to oxidation, but must also be expected to lead to reduction of the rate of formation of mutagenic aldehydes that arise as secondary products of lipid peroxidation, such as malondialdehyde, crotonaldehyde, acrolein and 4-hydroxynonenal. High rates of production of these mutagenic aldehydes must be expected simultaneously to lead to enhancement of the risk of various forms of cancer, and enhancement of the rate of mitochondrial DNA aging, which could lead to earlier onset of various age-associated degenerative diseases perhaps including type 2 diabetes. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2875212/