Zelber-Sagi S, Ivancovsky-Wajcman D, Fliss Isakov N, Webb M, Orenstein D, Shibolet O, et al. High red and processed meat consumption is associated with non-alcoholic fatty liver disease and insulin resistance. J Hepatol [Internet]. 2018 Mar [cited 2018 Mar 21];
This paper is just now starting to receive some discussion online, however, it came to be via the alerts service of my medical specialty society, the American Academy of Family Physicians (@AAFP).
This is a link to the actual brief, which caught my eye because of three things:
- Insulin Resistance
- Red Meat
- Israeli researchers (homage to the homeland)
Research links red, processed meat consumption to insulin resistance, NAFLD
A study in the Journal of Hepatology revealed that adults with high consumption of total meat and red and/or processed meat were at an increased risk of developing insulin resistance and nonalcoholic fatty liver disease, compared with those with low meat consumption. Israeli researchers conducted a cross-sectional study and found that an increased risk of insulin resistance was independently associated with high intake of meat that was fried or grilled and contained heterocyclic amines.source: Family Medicine Smart Brief, American Academy of Family Physicians
And actually, the brief didn’t link to the study, it linked to this: Health News Articles | News for Physicians & Medical Professionals, which then linked to the study, which is actually paywalled.
In this situation how would the average busy physician (or even would they) be able to verify the claims in the study?
This is, unfortunately, how more physicians are getting nutritional information than they probably should. It continues the tradition established in the 20th Century which I wrote about previously, complete with images from the medical journals of the past: Physicians’ 20th Century Nutrition Education: via Medical Journal Advertisements (Food Has Always Been Medicine)
I Pulled the Paper and I have a ton of questions
I had so many questions that I asked other doctors the questions I had to see if they were the right questions.
- The claim that non-alcoholic fatty liver disease (NAFLD) is caused by cholesterol, saturated fat, and lack of exercise
- The claim that red meat is associated with the development of insulin resistance, Type 2 diabetes, and metabolic syndrome
With that lead in, looking at the study itself
Noting, by the way the very high prevalence of
- diabetes, (14.8%),
- insulin resistance (30.5%), and
- NAFLD (38.70%)
The NAFLD prevalence is much higher than estimated previously (32 % – data derived from the same author of this study).
High meat eaters did not have significantly worse lifestyle habits, with similar levels of physical activity, smoking and sugared drink consumption, but had slightly higher alcohol consumption within the range of adequate intake, and as expected, higher consumption of saturated fat and cholesterol which were adjusted for in the multivariate analysis as potential confounding or mediating factors.
How did they know that they didn’t have significantly worse lifestyle habits, if they only controlled for these factors?
- Dietary cholesterol intake has not been shown to be a risk factor for metabolic disease
- Saturated fat intake’s risk factor profile for metabolic disease is questionable
See this article for more information: Just Read: Saturated fat does not clog the arteries: coronary heart disease is a chronic inflammatory condition, the risk of which can be effectively reduced from healthy lifestyle interventions
Did they control for the dietary determinants of Insulin Resistance and NAFLD?
- No review of carbohydrate intake, which is a risk factor for insulin resistance (and NAFLD) – what actually travels with meat eating in Israel? And if vegetable and seed oils travel extensively with meat in Israel (see photo below), how is this accounted for. I’m being mindful of the heart-breaking Israeli paradox.
Here’s a sample meal from a recent trip (I curated carefully, not ingesting the carbohydrate content)
Noting that the results changed to non-significance for “high processed meat” when adjusted for saturated fat.
Do the references represent the spectrum of scholarship on this topic?
I’m not sure about this. I am concerned that they don’t.
I think I’ll stop at 3 questions for now, because I did receive assistance from physicians who are more practiced in the review of nutritional science than I 🙂
1. Nutritional epidemiology almost always useless (weak associations, inconsistent trends, heavily biased, notoriously flawed questionnnaire-based methodology, more than 80% of nutrition epi studies later proved wrong in clinical trials). As the authors themselves write in their own conclusion: “This study has several limitations. Firstly, the cross-sectional design of the study does not allow causal inference. Secondly, meat consumption was self-reported and thus prone to reporting bias.”
2. Odds ratios in this article less than 1.5; OR less than 2 generally not considered worth paying attention to (signal:noise ratio too low).
3. the only type of carbohydrate they “controlled” for is sugary beverages; we don’t even have a basic total carbohydrate intake estimate, let alone a refined carb intake estimate–in other words, they didn’t ask questions or didn’t report answers to questions about processed carbs, which is a well-established risk factor for IR and absolutely must be taken into consideration in studies of IR-related diseases. Ignoring refined carb intake is the most common confounder of every anti-meat/anti-fat epi study I’ve ever wasted my time reading:)
4. Their *hypothesis* that HCAs are *associated* with disease is not only grounded in similarly weak epi studies (they acknowledge themselves in the paper there is no human clinical evidence), it also conveniently overlooks the facts summarized on the slide below (from my WHO red meat and cancer presentation). Those are just for starters.
Last thing, I did send a note to my colleagues at @AAFP – this is the last part of it:
Happy to discuss this further & especially if there’s a way to have studies about emotional topics like nutrition to only be linked to if they have a good basis in science. If there are workgroups at AAFP working on the nutrition question around diabetes and diabetes reversal, I am happy to connect with them in the interest of relaying information of high integrity to our membership :).
Many thanks for listening,
Ted Eytan, MD
Board Certified Family Physician
Washington, DC USA
I received no response.