Some individuals may experience digestive discomfort, bloating, gas, or diarrhea after consuming whey protein, but this will depend on the dose and one’s tolerance. Whey protein concentrate contains the milk sugar lactose, so individuals with lactose intolerance may want to avoid this form of whey protein in favor of isolate/hydrolysate (which don’t contain fat and contain very little lactose, making these forms of whey protein tolerable by all but the most lactose-sensitive individuals).
Whey (and protein in general) does not harm the liver or kidneys, but high-protein diets can exacerbate or accelerate pre-existing damage. People with damaged livers or kidneys should exercise caution when increasing protein intake quickly without the guidance of a doctor. See more below: FAQ:can-eating-too-much-protein-be-bad-for-you-3
Furthermore, a 2018 report on protein powders found that of the 134 products tested, over 70% of them had detectable levels of lead and cadmium. However, no data were reported on whey protein powders specifically and it should be noted that “detectable” does not necessarily mean harmful.[1]