Meat, plants & TMAO

Executive Summary

* A study has just been published with findings from a crossover trial where 36 participants consumed plant-based 'meat' vs animal meat 2-3 times a day.

* The study was funded by the plant-based ‘meat’ company Beyond Meat.

* The primary outcome of interest was TMAO (trimethylamine-N-oxide). TMAO is known to increase following consumption of meat, eggs and especially fish. Choosing TMAO as the primary outcome of interest was highly likely to find in favour of plant-based ‘meat’.

* TMAO did increase, but interestingly only in the 18 people who did the animal phase first, followed by the plant phase. Those who did the plant phase first and the animal phase second, had no significant increase in TMAO.

* The paper implied that TMAO is harmful but did not provide evidence for this. There is limited evidence (from population studies) of an association between TMAO and cardiovascular disease (CVD), but causation cannot be claimed.

* A number of other researchers, who have investigated TMAO and disease, have concluded that it might be a marker for something else but "TMAO is not the bad guy of heart attacks and stroke that we’d previously thought."

* The most significant 'black swan' in the TMAO/disease debate is that fish is the richest source of (preformed) TMAO and fish is not claimed to be a risk factor for death or avoidable disease – usually on the contrary.

* This was a well-executed study, with multiple measurements, but it found nothing of real significance. The funder will likely be content, however.


I spotted this week’s story on twitter in Dr Christopher Gardner’s timeline. I had some communications with Dr Gardner in February 2018 about his low carb vs low fat study (Ref 1). Gardner himself is a “longtime vegetarian” (Ref 2). Gardner is the senior author on a paper that has just been published in the American Journal of Clinical Nutrition (Ref 3). He tweeted a summary of the findings as follows:

Better with plant: TMAO, LDL-C, weight

“Better with animal: nada

”No diff: IGF-1, HDLC, TG, gluc, ins” (Ref 4).

The conflicts are important to note up front. In what follows, CDG is Chris D. Gardner: “CDG received funding for the study from Beyond Meat in the form of an unrestricted research gift made to Stanford University.”

Gardner also asked in a tweet “can we get some love for the study name/acronym? Study With Appetizing Plantfood – Meat Eating Alternative Trial SWAP-MEAT” (Ref 5). So, a study funded by meat alternatives was entitled SWAP-MEAT (for alternatives). I detect confirmation bias.

The study

The aim of the study was to compare the effect of consuming plant-based ‘meat’, as opposed to animal meat. The study involved 36 participants, of whom 67% were female and 69% Caucasian. The average age was 50 and the average BMI was 28. The participants were randomised to either the plant or animal intervention for the first phase. They were instructed to consume ≥2 servings per day of plant-based ‘meat’ or animal meat for 8 weeks and then to swap over to the other intervention. They were supposed to keep all other foods and drinks as similar as possible between the two phases. This was a crossover trial, therefore. There was no washout period – the participants started the other intervention as soon as they had finished the first (this may have been important – we’ll come back to this).


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