I brought in 2X5KG bags of whey protein powder to New Delhi from UK and as it was for my own consumption I did not declare it at customs. Customs normally look for gold and other stuff that are smuggled in to make a profit and evade taxes.
I have worked at New Delhi IGI T2 for some time in the past and from my experience they do not bother people who carry quantities of items that are not enough to cover traveling expenses. This does not mean that you will not have to pay customs duty if they do single you out at random for a manual check which they some times do.
Customs duty for whey protein is 30% which adds up to about 35% after adding all the cess they add on top. It would still turn out to be cheaper after paying 35% and you will have the peace of mind that it is not adulterated which is some times the case with products sold in India.