I used another clinic from the ones I usually donate blood. The doctor that was responsible for taking my history in regards to approving me as a donor after the usual questions asked me if I use protein supplements. I answered truthfully that I do (about 40 g of whey protein powder daily), and after advising me to reconsider that lifestyle-wise, they told me they would allow me to donate blood this once but even then would only keep the red blood cells of my donation.
In the past 9 years, I've been a donor I never had this come up. Is there an established, widely accepted valid reason for this or is it the doctor's personal opinion to exclude people consuming whey protein supplements from donating blood?
If the first one, how it would be any different than just adding the equivalent of that dosage in protein-rich dairy products instead of the protein powder?
Do note that I was asked if I take protein supplements and not if I have a protein-rich diet to begin with.