Congrats! I went through this thought process as well, and one of your three hypotheses above seems like the right one. Vitamin D isn’t the issue (I have tests for it and have heavily supplemented for years), and sulfur itself isn’t an issue (onions and broccolo are both pretty big in my diet). However, the lack of sulfur amino acids is the lead hypothesis.
Over the years, I had slowly shifted my diet more and more plant based: lots of vegetables, with occasional meat and a piece of fish every couple of days. As you mentioned, not all protein is created equal. While both vegetables and meat both contain all 20 amino acids, the ratios matter. Bodybuilders eat animal protein instead of vegetable protein for very good reason. I try to be active and try to keep muscle on my frame, and the plant based sources were just not providing enough of the key unsynthesizable amino acids.
Congrats! I went through this thought process as well, and one of your three hypotheses above seems like the right one. Vitamin D isn’t the issue (I have tests for it and have heavily supplemented for years), and sulfur itself isn’t an issue (onions and broccolo are both pretty big in my diet). However, the lack of sulfur amino acids is the lead hypothesis.
Over the years, I had slowly shifted my diet more and more plant based: lots of vegetables, with occasional meat and a piece of fish every couple of days. As you mentioned, not all protein is created equal. While both vegetables and meat both contain all 20 amino acids, the ratios matter. Bodybuilders eat animal protein instead of vegetable protein for very good reason. I try to be active and try to keep muscle on my frame, and the plant based sources were just not providing enough of the key unsynthesizable amino acids.