The ability to digest lactose probably spread like wildfire because it was a genetic mutation and those with the mutation had a new source of nutrition they could take advantage of which helped them survive better than those without.  So, as a result, most Europeans now are lactose-tolerant.<p>Personally, as someone of northwestern European ancestry, I seem to do just great with a lot of milk in my diet.  But back when I was younger and drank a lot of soda with HFCS, I got fat.  But I wouldn&#x27;t expect someone of, say, Asian ancestry to do so well with a lot of milk; they probably wouldn&#x27;t even be able to drink it without having a lot of gas problems or needing to add lactase (or buy &quot;Lactaid&quot; brand milk).<p>What we really need is nutrition advice that&#x27;s tailored for an individual&#x27;s genetic profile, and probably also of the genetic profile of their gut bacteria.