Vegetarianism is mostly genetic, claim Wesseldijk et al.

I found this topic first from a short snippet in The Week, then from the news article https://www.smithsonianmag.com/smart-news/maintaining-a-vegetarian-diet-might-be-in-your-genes-180983021.

Remove the dot at the end, otherwise it's a dead link.

It is important to note that behavior is always in relation to an environment, so we can't say that some behavior is 70% caused by genetics, the most we can say is that something is 70% caused by genetics in this specific environment. This is easy to check with a thought experiment, lets take these people whose "willingness to stick with veg*n diets, regardless of their stated reasons, are 70-80% inborn" lock them in a vegetarian Hindu monastery and you'll obviously see the rate of vegetarian diets skyrocket. So when you write "Vegetarianism is mostly genetic, claim Wesseldijk et al." Wesseldijk herself would say:

Yet, as Dr. Wesseldijk reminded me in an email, high heritabilities do not imply that biology is destiny. According to surveys by the Vegetarian Resource Group, the percentage of Americans who are vegetarian or vegan jumped six-fold between 1994 and 2022—from 1% to 6%. This impressive change in patterns of meat-eating was due to shifts in cultural attitudes, not changes in our DNA.

And to tie it in to the Hindu monastery (from the same article):

It is important, however, to keep in mind that estimates of heritability only apply to the populations that the subjects in the studies represent. Most of the individual differences in meat-eating among the Dutch are rooted in genes, yet culture is almost entirely responsible for the fact that per capita meat consumption is 20 times higher in the Netherlands than it is in India.

Or as Dr. Wesseldijk has also phrased it:

An environment can completely counteract something that is highly heritable, and the same goes with vegetarianism

As someone who has done vegan advocacy for a long time, this matches with my experience unfortunately. A meatless diet just "clicks" with some people, while with others it's a near impossibility to get them to sustain without meat (let alone other animal products). A genetic component would certainly explain my observations, because there definitely seems to be something deeper than underlying belief or commitment going on. 

If anything, this further underscores the need for cellular agriculture (lab-grown meat / eggs / dairy, without harm to animals). We need to find a way to make these foods cheap and cruelty-free, since universal veganism / vegetarianism may not be possible (although there are certainly a lot of cultural barriers that can be addressed first). 

I've talked about this a bit in the post you cited, and happen to have recently commented on it. I haven't dug into the genetics or tried to quantify the effect because I don't expect the data to be very actionable at this stage. We're years from having specific treatments based on genetics, most studies are very bad, and I think self-reports and veg*nism attrition rates should be enough to convince people that people vary widely and you need to plan for that in full generality. 

I would appreciate it if someone with technical competence assessed the reliability of this study and its findings.

Doesn't pass the sniff test for me. Two concerns:

1. Every vegetarian I've met or heard of is vegetarian because of either a) animal welfare, b) climate change or c) cultural tradition. It seems very unlikely that any of these factors could be strongly genetic.
2.  They're determining genetic heritability by comparing identical twin pairs with non-identical twin pairs (i.e. if the identical twins are more similar in their preferences than non-identical twins, they assume that there's more of a genetic component). I imagine that there could be lots of confounders here. Growing up as an identical twin is a different experience to being a non-identical twin. There could be different environmental factors between the two situations (e.g. maybe identical twins tend to feel closer and more closely mimic each other's behaviours/choices).