The Identical Twin "Vegan vs Omnivore" Study Debunked

How to take a negative study and present it as a win for vegan diets.

Two recently-published clinical trials have examined vegan diets, and in both cases the results fail to live up to the hype.

Today, we’ll look at the shorter of those two trials. This was a study involving identical twins that has been receiving favorable press. To believe some news articles, this study even found vegan diets can extend longevity, a truly ridiculous claim given that it lasted all of eight weeks.

Upon reading the study for one’s self, it quickly becomes apparent it is not the glowing endorsement its authors, the media, and vegan influencers make it out to be.

Quite the opposite, in fact.

As to why the study authors might be motivated to find benefits for veganism that don't exist, one of the study authors was Christopher D. Gardner, who has received funding from fake meat company Beyond Meat.

Gardner and three other of the study's authors - Jennifer L. Robinson, Tayler Hennings, Justin L. Sonnenburg - also received funding for the project from the Vogt Foundation - a major funder of anti-meat projects.

The Vogt Foundation's 990 forms for 2020 through 2022 (available here) show the hefty sum of US $850,000 was gifted to the makers of The Game Changers - a terribly flawed, dishonest and hypocritical vegan crockumentary that I dismantled here and here. Ironically, The Game Changers made much ado about studies funded by meat/dairy/egg concerns, but had absolutely nothing to say about the many studies funded by those with a heavy financial or ideological interest in 'plant-based' diets. In fact, the documentary itself was hopelessly conflicted, with executive producers James Cameron and Suzy Amis Cameron, Executive Producers also being the owners of Verdient Foods, which in 2018 announced it was investing a hefty $140 million to expand into a range of plant-based proteins. Another executive producer, Chris Paul, is an investor in Beyond Meat,

The same 990 forms show from 2019 through 2022, the Vogt Foundation also gave US $1.5 million to the so-called Good Food Institute. This Washington DC outfit describes itself as "a nonprofit think tank and international network of organizations working to accelerate alternative protein innovation ... By making meat from plants and cultivating meat from cells, we can modernize meat production."

Vegan proponents get pretty loud when they notice potential conflicts of interest in studies showing favorable results for animal foods. When rampant conflicts of interest exist in research portending to find favorable results for “plant-based” diets, they simply look the other way and pretend they didn’t see anything.

Not. Very. Ethical.

The Study Methods

In 2022, the Stanford researchers randomized 22 pairs of healthy, adult identical twins to a “healthy” vegan or omnivorous diet for 8 weeks. One twin dropped out, leaving 21 pairs of mostly female twins that completed the 8-week intervention.

That the study was a complete farce becomes immediately evident when the researchers declare the primary outcome to be "the difference from baseline to 8 weeks in low-density lipoprotein cholesterol (LDL-C) levels between the diet groups."

Here we are, over two decades into the twenty-first century, and researchers are still wanking on about LDL cholesterol. To maintain this idiotic obsession with such an irrelevant ‘risk marker’ at this stage of the game is an absolute disgrace. Science is capable of so much more than just being a propaganda vehicle to prop up disproved theories that benefit no-one except pharmaceutical companies, manufacturers of cholesterol-lowering foods, grant-sucking ‘lipid researchers,’ and the plethora of corrupt heart associations/foundations around the world that charge food manufacturers for ‘heart healthy’ ticks and checks.

Secondary outcomes in the study were a mix of important (vitamin B12), sometimes relevant (body weight, fasting triglycerides, glucose, insulin) and waste-of-time wankery (HDL cholesterol, total cholesterol, trimethylamine N-oxide (TMAO)).

During the first four weeks of the intervention, the participants were provided all meals free by a nationwide meal delivery company. During the following four weeks, participants were assumed to have gotten the picture and were responsible for their own food purchases and preparation.

Participants were told to eat until they were satiated throughout the study.

As you would expect in a randomized study involving identical twins, baseline characteristics of the two groups were similar, with one notable exception: For some reason, mean plasma vitamin B12 level was initially higher in the vegan group (590 vs 492 pg/ml), with individual values also spread over a far greater range in that group.

Initial weight was similar between the two female groups, but males assigned to the vegan group were a mean 4 kg lighter at baseline than males assigned to the mixed diet group.

One of the numerous pairs of twins that participated in the trial.

The Study Results

At eight weeks, participants receiving the vegan diet showed a mean decrease of 13.9 mg/dL in mean LDL cholesterol levels from baseline. LDL levels remained essentially unchanged in the omnivore group, resulting in final readings of 95.5 versus 116.1 mg/dL.

No significant differences were observed between groups for HDL, triglycerides, TMAO and glucose.

At the end of the study, fasting plasma insulin levels in the vegan and omnivore groups were 10.5 and 13.7 μIU/mL, respectively. The difference was statistically significant, but of doubtful clinical significance given the normal range for fasting insulin is 2-20 μIU/mL.

The vegan participants lost 1.4 kg during the eight weeks, while the omnivore participants remained weight stable. The researchers treated this like a win for the vegan diet, but a reality check is in order.

Firstly, this was not a weight loss study, subjects were given no weight loss advice and were not prescribed an energy deficit - they were simply instructed to eat until satiated. The data showing lower dietary satisfaction in the vegan group (more on that in a moment) suggests the reason for the weight loss was simply because that group found their diet less palatable.

Secondly, at least some of the participants would have been best served avoiding weight loss. There was a higher proportion of female twins (17 pairs at baseline) in the study, and they began the study with a mean BMI of 26.9, rendering most of them officially overweight.

In contrast, the baseline BMI of the male participants was 22.8, well within the suggested range of 20-25. To put those figures into better perspective, the baseline weights of males randomized to the vegan and omnivore groups were 68.7 and 72.7 kg, respectively.

Heights are not presented, nor are separate mean ages by gender, but mean age for the entire cohort was 39.6 years.

Weight loss results by gender are not presented, only for each group as a whole. If the weight loss extended to the male participants then, given the importance of maintaining lean mass and avoiding underweight as one ages, it’s hard to get excited about weight loss in a group of already slightly-built men. If you’re a dude of average height approaching 40 and you weigh only 68.7 kg, then some muscular weight gain might be a prudent idea - not just to look better in a t-shirt, but to guard against falls and fractures as you age (vegans are at higher risk of bone loss and fractures).

If the weight loss was confined to the female vegan subjects, then a 1.4 kg weight loss over 8 weeks in subjects with a mean BMI of 26.9 is nothing to write home about. The subjects in that group began the study overweight, and finished it overweight with a BMI of 26.4.

The Study’s Important Finding that Was Ignored

A look at the supplementary dietary data shows, not surprisingly, that vitamin B12 intake plummeted during the vegan diet intervention.

So despite starting out with a mean higher plasma B12 level ( (590 vs 492 pg/ml), the vegan group finished with a nominally lower level (470.9 versus 492.8 pg/ml).

The change was not statistically significant, but we all know what would have inevitably happened had the study extended beyond eight weeks: Plasma B12 levels would have continued to decline and reach deficient levels, as they do in most vegans who fail to supplement.

This was the most important finding in the study, yet the researchers barely gave it any heed, instead dismissing it with the throwaway line, “Long-term vegans are typically encouraged to take a cyanocobalamin (vitamin B12) supplement.”

If you intend to follow a vegan diet, supplementation with B12 is a must, not something to ponder after being “encouraged” (and rather than cyanocobalamin, I’d recommend the methylcobalamin form for superior absorption).

I Can't Get No Satisfaction

In the main paper, the authors briefly touched upon diet satisfaction, writing "Participants receiving the omnivorous diet had nominally higher diet satisfaction at weeks 4 and 8 compared with vegan participants."

Here's what they wrote in the supplementary material, which far fewer people will read:

"Within the vegan diet arm, diet satisfaction decreased on every scale apart from the healthy lifestyle scale, which increased at weeks 4 and 8 relative to baseline. Notably participants assigned to the vegan diet arm reported the largest decrease in diet satisfaction when eating out at weeks 4 and 8 relative to baseline. Among participants in the omnivorous diet arm, diet satisfaction either increased at weeks 4 and 8 or was maintained from baseline reported levels."

When asked at the end of the study if they planned to "Continue to closely follow all recommendations for my eating pattern," 28.6% of the omnivore participants replied in the affirmative, compared to only 4.8% of the vegan group.

The supplemental data also shows significantly higher proportions of vegan participants reported lack of satiation and dissatisfaction with food variety and inclusion of foods they did not like.

Much Ado About Nothing

The only biochemical finding of relevance in this study - a rapid drop in plasma B12 among those assigned to a vegan diet - was ignored. Instead, the researchers praised the reduction in LDL cholesterol levels during the vegan intervention, concluding “Clinicians may consider recommending plant-based diets to reduce cardiometabolic risk factors, as well as aligning with environmental benefits.”

This was, quite frankly, a stupid thing to conclude.

The study established exactly zero environmental benefits for “plant-based diets” - environmental outcomes were not examined in this trial.

As for reducing “cardiometabolic risk factors,” clinicians need to decide what is really important - saving lives, or continuing to participate in the emperor-has-no-clothes farce that is the Great Cholesterol Con.

I presented several lines of evidence in my 2005 JPANDS article “LDL Cholesterol: “Bad” Cholesterol, or Bad Science?” showing LDL cholesterol does not cause atherosclerosis, coronary heart disease or stroke. The full paper is freely available here*; my response to ill-conceived criticism by two researchers (one hailing from the Scripps Institute) can be viewed here (scroll to page 2).

More recently, a 2022 systematic review and meta-analysis of statin drug trials published between 1987 and 2021 found that not only were the benefits of these drugs exaggerated, but there was no consistent relationship between the degree of LDL reduction and clinical outcomes. If LDL cholesterol causes cardiovascular disease and mortality, then there should be a clear, consistent relationship between the degree of LDL reduction and the magnitude of reduction in clinical outcomes.

The reason there is no such relationship is because the entire cholesterol theory of cardiovascular disease is a highly lucrative fraud, something I explained at length in The Great Cholesterol Con. The reality is that cholesterol is a critically important substance found in our cell membranes. Its presence in some atherosclerotic plaques reflects its role as a repair substrate. Blaming cholesterol for atherosclerosis is every bit as stupid as blaming paramedics for causing the carnage at an accident scene they are attending.

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*For anyone wishing to make contact after reading that paper, please note my given email address is no longer valid. Try info [at] anthonycolpo [dot] com instead.