TLWR: There is a strong, scientifically backed connection between Branch Chain Amino Acids (especially leucine) and acne. Leucine is the most important amino acid for muscle growth and is overly prevalent in most protein powders. When I stopped taking protein shakes, my acne of 20+ years completely disappeared.

My acne story is similar to most long-term sufferers: started in teenage years; success with some treatments, less with others; eventually settled onto something that sort of worked most of the time (which was a modified version of The Regimen, the only thing I'd had consistent success with).

Ive lifted diligently for 20+ years. With that, Ive taken protein supplements every day this entire time (40 to 80 grams, depending). About a year ago, I started adding Branch Chain Amino Acids to my shake, and my acne flared up to the worst its been in years. I figured it was just another flare up so I went to the dermatologist and got a round of antibiotics as usual. The antibiotics were mostly effective, but my acne returned quicker than usual. So I googled Branch Chain Amino Acids and acne and found the following:

Relationship between serum amino acid levels and acne severity

https://www.sciencedirect.com/science/article/pii/S1687850723001929

Dietary intervention in acne

https://pmc.ncbi.nlm.nih.gov/articles/PMC3408989/

I stopped taking the Branch Chain Amino Acid supplement, and my acne calmed down but didnt go away. So I started reducing my daily shakes to only five times a week, and my acne improved. Then I reduced it to once a week, and my acne improved significantly. Then I ceased ALL protein supplementation, and my acne stopped completely after two weeks. This was almost six months ago and I havent had a single blemish even AFTER stopping all acne face treatment other than a simple Benzoyl Peroxide facewash twice a day. No more creams. No more pills. Just facewash and lotion. And I suspect I could switch out the Benzoyl Peroxide for a regular facewash.

20+ years of acne cured by stopping the one thing Id been doing consistently: drinking protein shakes. Ive lost some of my precious, precious gains in the gym, but its worth it to have clearer skin and no more acne hassle!