The tldr is he created a virus then ate it to make his digestive system have more of the gene that makes lactase as he was very intolerant. 2 years later the effects are starting to wear off as cells get replaced but it seems to have had a very high ROI
There’s a great youtuber called the thought emporium who did genetic engineering on himself. I highly recommend checking them out :
https://www.youtube.com/watch?v=J3FcbFqSoQY
And the 2year follow up: https://www.youtube.com/watch?v=aoczYXJeMY4
The tldr is he created a virus then ate it to make his digestive system have more of the gene that makes lactase as he was very intolerant. 2 years later the effects are starting to wear off as cells get replaced but it seems to have had a very high ROI