The problem is that whey causes problems in the adult gut microflora causing gastrointestinal issues and stomach upsets.
Most of the side effects from whey protein are related to digestion.
Some people have problems digesting whey protein and experience symptoms such as bloating, gas, stomach cramps and diarrhoea.
Because whey protein comes from cow’s milk, people with a cow’s milk allergy may also be allergic to it.
Gut flora is involved in weight stability and whey protein can disrupt the gut flora by facilitating weight gain or loss.