I should have added that it's more complex than a simple low-B12. My blood work results have regularly shown low hemoglobin. It causes a lot of issues like inability to catch my breath, fatigue, and weakness as well as a foggy mind. The diagnosis was an Iron/B12 deficiency which is, IIRC, correlated. I don't have a ton of detail, myself. I had no leanings toward become a vegetarian so I didn't question his orders there. (edit: it's not completely related, but I'll note that my younger brother is vegetarian as his wife is vegan and he's as large as I am—maybe larger—and does just fine without poultry, red meat, or fish. Luck of the draw, it seems).

I'm certainly not saying there are no routes to surviving well as a vegetarian maintaining some form of anemia or other B12/Iron deficiency, but I'm assuming his direction was that due to its proven concentration.

I actually increased my diet of eggs, spinach, I'd long taken a cyanocobalamin orally daily before switching to a higher dose of methylcobalamin sublingual dose, and started eating yogurt.

I try and avoid an excess of cheese and grains because I simply don't need that much in the way of fats and carbohydrates in my current regimen.

Nutrition is complex, and I think it's generally accepted that acquiring nutrients through digestion is more reliable than supplementation. (so that I'm not saying this completely out of my ass, [0] [1])

[0] https://www.nature.com/news/nutrition-vitamins-on-trial-1.15...

[1] https://www.scientificamerican.com/article/fact-or-fiction-v...