Since whey protein isolate is derived from the process of turning milk into cheese, it’s one of the more natural protein sources you can find in supplement form.  Usually any side effects associated with whey protein are the result of impurities or additives that may be found in whey protein supplements that are not 100% pure.  To reduce the possibility of any negative effects, always select whey protein isolate that is certified as pure and do not exceed the recommended dosage as indicated by the manufacturer label.   The other possibility for side effects associated with whey protein is if you are lactose intolerant or have an allergy to dairy or lactose.  While whey protein isolate has been reduced down to its purest protein content, with as much fat and lactose removed as possible, some people with allergies or intolerance for lactose and dairy may experience ill effects from whey protein isolate.

See also:

1. Whey Protein Side Effects – Not What You’d Think
2. What Is Whey Protein Isolate?
3. Whey Protein Isolate Review