A number of years ago, a group of French doctors tested for
intolerance to milk fat. They found that 9 of the 100 people in
their test group suffered symptoms when exposed to milk fat 
but not when exposed to milk sugar (lactose).

They did the experiment in the first place because, they said, 
the French, as well as the Spanish and Italians, find skimmed 
milk more "digestible" than regular milk.

Unfortunately, I do not know of a single follow up experiment 
in all the years since.

Steve Carper