Dr. Ivan Pavlov, the man best known for his ground-breaking work with stimulus/response, is the first scientist to study it.
Also, Dr. Herbert Shelton is the best known for it.
Basically, some foods should not be eaten with others as some food combinations are destructive to our internal system and thus robbing us of energy.
Some of the bad food combinations are eating together: meat and potatoes, cheese and bread, milk and cereal or fish and rice.
The basic chemistry applies, as different types of foods require different types of digestive juices, and not all digestive juices are compatible.