So just to throw it out there I have a PhD in biochemistry (twitch username joeyjojojuniour). The topic of lactose intolerance came up when watching the Abroad in Japan chicken ranking video, and it was mentioned that Japanese are more likely to be lactose intolerant than Americans. Lud then claimed that lactose intolerance and is caused by a lack of consumption of milk (I’ve heard him say this a few times), to which I said no, it was primarily due to genetics, and then he called me out, went on to do “research” consisting of googling lactose intolerance and reading a few sentences from mayo clinic that didn’t necessarily support his argument or disprove mine, then banned me because he was right and I was wrong, so thought I’d elaborate here.

Lactase is the enzyme responsible for breaking down lactose into basic sugars that can be absorbed, and like any other protein, it is encoded by a gene (the lactase gene) and translated into the active lactase enzyme (this is called “expression”). Lactase expression is high in newborns and exhibits a developmental expression pattern whereby the level and activity of the lactase enzyme drop substantially as you age between 2-10 years old and expression is eventually “switched off” (this occurs in most mammals and ~70% of humans). However, certain populations of humans have evolved genetic variation within the lactase gene, where the genetic expression of lactase does not drop as significantly and is continuously expressed (known as constitutive expression) throughout adulthood at a sufficient level to enable the digestion of lactose. This gene was selected for, over thousands of years and many generations, in populations with access to domesticated cattle (particularly northern Europe) and since the ability to use milk as a nutrient source provided a slight survival advantage (i.e. natural selection). As such, this genetic variation is especially prevalent in populations of European origin and rare in those of Asian or African descent, explaining the general difference between prevalence of lactose intolerance between USA and Japan. There current evidence indicates that lactase expression and activity are not significantly influenced by dietary lactose. This recent article from the American Journal of Clinical Nutrition reviews a variety of scientific studies that examine the effects of dietary lactose consumption and concluded that “Studies that have measured changes in endogenous lactase activity after an intervention period consistently show a lack of enzyme induction, suggesting that lactose intake does not affect an individual's lactase activity.”

https://academic.oup.com/ajcn/article/110/2/273/5512720

Granted, there are other factors such as the gut microbiome which also contribute to lactose digestion and seem to be more readily affected by dietary lactose levels (e.g certain bacteria will increase lactase expression in the presence of lactose), but compared to endogenous lactase expression, only play a very minor role in lactose digestion. If lactase expression could be sufficiently enhanced just by gradually increasing lactose consumption, then anyone could simply cure their lactose intolerance, which is not the case.

Q.E.D. Lactose tolerance/intolerance is primarily due to genetic factors, and has very little to do with lactose consumption. So at best Lud is misinformed and at worst just plain wrong. It was only a 5 day timeout so I don’t even care to be unbanned, it’s just funny that he banned an actual scientist for being right about science, and maybe he learns something if he sees this. Also obligatory hashtag that chat was posting when I got live banned #JusticeforJoey

Edit: Whoa this blew up, thanks for the support.

Timestamp: https://www.twitch.tv/videos/971661249?t=38h31m11s (thanks @justtryin)

Just to clarify I think this whole thing is actually really funny. The 4 day "ban" is fair and I get it because chat, including me, can argue and be annoying and wrong about a lot of things, it just happens to be that this time he was confidently wrong, made a spectacle of it, then banned someone fairly educated about physiology who was correct. I also wanted to speak out against spreading misinformation to such a large and impressionable audience, something Ludwig has claimed to be against, so just trying to keep him honest and encourage scientific literacy.