SELECT count(*) FROM Has_allergy AS T1 JOIN Allergy_type AS T2 ON T1.allergy  =  T2.allergy WHERE T2.allergytype  =  "food"
How many students are affected by food related allergies?
[Schema (values) (types)]: | allergy_1 |  Allergy_Type : allergy (text) , allergytype (text) | Has_Allergy : stuid (text) , allergy (text) | Student : stuid (text) , lname (text) , fname (text) , age (number) , sex (text) , major (number) , advisor (text) , city_code (text);