Some people report feeling heaviness and indigestion when they consume whey protein. This is due of one of two reasons, the more common culprit is lactose intolerance. Lactose is a sugar found in milk and subsequently whey protein, a lot of people all around the world cannot digest lactose efficiently and this results in digestive issues. If you are lactose intolerant and you still wish to consume whey, we would recommend investing in our isolated whey product. The other culprit is adulteration as some brands tend to spike their whey protein with cheap amino acids and additives to cut costs which can result in digestive distress. The best way to check for genuine supplements is via third party testing reports.