you have already had excellent advice but just to reassure you- i have been to India twice, and to Morocco and Egypt (the latter camping in a bedouin place- well it seemed like a good idea at the time!) and have never been sick. i have been in both cheap and middle range accommodation, used public transport, travelled around A LOT. my top tips:
take the probiotic as someone else has said- start taking them about one month/2 weeks before going, and keep going while you're there. in fact if he has a sensitive tummy it's a great idea on its own
be religious, no, obsessive about washing hands. it really is key.
stick to vegetarian food, readily cooked. no buffets. no salads. no fruit unless still with skin on (and obviously peeled). no food from the hotel minibar.
drink only bottled water, and use it to brush teeth too.
if at all unsure about the cleanliness of knives and forks- use your hands! (after having washed them well, obviously). most indians use their hands anyway, and cutlery may not be regularly washed. (this tip i got from an indian friend)
do not assume that posh places are a safer bet than mid range ones- in fact they may be less safe if turnover of food is less frequent!
if you are really really worried- get his gp to prescribe a wide ranging antibiotic before he goes, which he can start taking at the first sign of illness (seem to remember i got that from my gp before my first trip).
wherabout is he going? in my experience (limited!) south india much cleaner than north india!
last but not least- i hope he doesnt get too stressed about it, indian food is amazing and deserves to be enjoyed, and india is an amazing place!!!