Not only can certain foods cause problems for different people (digestive issues, itchy skin, gas etc.) but even wrong COMBINATIONS of simple foods can cause issues. Even wrong combinations of spices can be a problem for some. Why would a wrong combination of foods cause problems? Because when foods are combined, they become a new entity. Also, the digestive system works by sending out digestive juices to digest various products. If you mix something that requires a certain digestive enzyme with another food that requires a different one, that can cause stomach pains, gas, indigestion etc. 

Contrary to popular belief, proteins and starches do not often combine well. So potatoes and steak are not a good combo for many people. Steak and a salad or non starchy vegetables go better. 

Lentils and potatoes do not always combine well. Lentils with tomatoes and do however.

Fruits do not combine well with starches. Nuts do not combine well with certain flours etc.

Dried fruits do not combine well with flours.

And it is not only about combinations. It is also about the order of eating. Even Maimonides recommends eating lighter foods before heavier ones: fish before chicken or meat, chicken before meat, salads before heavier foods, fruits either before a meal or in between meals (not generally after a meal).

It also depends how many different foods are served at one meal: the more, the harder the digestion.

Each person must find out what things bother their stomachs and adjust their meals accordingly.