I never heard of lactose intolerance until maybe ten or twenty years ago. Everyone ate milk and cookies and peanut butter and jelly sandwiches when I was a kid. Who didn't eat ice cream? Also grilled cheese sandwiches. American cheese or Velveeta if not fancy cheeses. Sometimes I think it's one of those diseases that people just think they have because it's going through a "popular" phase. There's another illness regarding food that's going around now like that. I don;t recall the name right now.
Increases in peanut allergies is a very real thing; it's not made up like the majority of people saying they cant eat gluten. Now we dont fully know why it is increasing, but all evidence is pointing us living cleaner lives that actually does not allow our immune system to fully develop. On top of that, too much bad information with little to no scientific backing was spread around to new parents, such as dont let you child eat peanut butter when young. As it turns out though, feeding babies peanut based products decreases the chances significantly that they will develop a peanut allergy.
Insofar as being lactose intolerant, well about 90% of Europeans are lactose tolerant. Since roughly the majority of the USA are of European descent for a rather long period of, you would expect this to not have been a big deal in generations past. But since 70% of world is lactose intolerant, as that changed, this would become more and more problematic.
FYI, lactose tolerance is not a use it or loose deal either. It is a genetic mutation where your body will continue to produce lactase (the enzyme to break down lactose) past childhood that never goes away.
PS. the so called gallon challenge, where you try to drink a gallon of milk without vomiting, has nothing to do with lactose or dairy. It is due to your stomach not being big enough to store a gallon of any liquid. If you try it with water, unless you are very dehydrated, you would vomit too.
