Whey protein is a by product of cheese which some people are allergic to. In fact some who are not allergic normally to cheese find if they eat too much can experience stomach upset or flatulence, but otherwise for the stuff is harmless they think. Studies are still being conducted to find out if whey protein can cause kidney and/or liver damage, and if it can lead to Osteoporosis because protein can lead to a mineral imbalance effecting the bone mineral density. As with any product promising "miracles" do your research first and don't over indulge.