Basically, a person may have trouble breaking down a food, perhaps because of enzyme deficiencies or because of chemicals found in the food that are difficult to process.
जैसे कुछ लोगों को लैक्टोस इंटॉलरन्स होता है, यानी वे दूध या उससे बनी चीज़ें नहीं खा पाते हैं ।