Milk, Dental Decay + Lactose Intolerance

I thought I’d impress my dentist today during my 10-minute £65 checkup.

I mentioned a fascinating book I’ve been reading about a dentist in the 1930s who travelled the world studying the diets of remote and isolated populations to understand tooth decay and mouth development.

Sounds a bit dry? Maybe. But I gave him the summary anyway — and he didn’t flinch.

The book’s preliminaries were overlong (which, for some reason, I always feel obliged to read), but now we’re into the main course and it’s genuinely very good.

The author’s first stop was Switzerland. Even 100 years ago, some mountain settlements were so isolated they had no roads and barely any contact with the outside world. Their diet was simple: rye bread, dairy (milk, cream and a lot of cheese), vegetables grown in incredibly fertile soil during a very short summer, and meat perhaps once a week.

Dental outcome?

Almost no decay.

Add wine into the mix, and the fillings suddenly appeared.

At this point, my dentist clearly was listening because he chimed in about lactose intolerance — something I hadn’t fully appreciated.

Most humans worldwide become lactose intolerant after childhood.

The default biology is:

• infants produce lactase (the enzyme needed to digest milk)

• lactase production drops after weaning

• most adults become lactose intolerant to some degree

Europeans are the exception.

Northern and Western Europeans have unusually high lactose tolerance rates — often 80–95%.

This is unusual because most Indigenous populations globally have high lactose intolerance.

Why?

Europeans developed a genetic mutation called lactase persistence, which keeps lactase switched on throughout adulthood. It evolved alongside dairy farming and is considered one of the strongest examples of recent human evolution.

Next up in the book is Lewis in the Western Isles of Scotland. Apparently they also had incredible teeth — and they ate oats with EVERYTHING.