I have a natural b12 deficiency and can’t eat a vegetarian diet right now because of it. At the same time lactose intolerance runs in the family (though I don’t have much of a problem wth it). My doctor ordered me to eat more red meat. The difference in my overall well-being has been exponential over the past two years because of it.

Not questioning this, but curious if you can explain more. Why can't you just do one or many of:

Taking a B12 supplement, eating fortified food (american breakfast cereals often have B12, especially the "healthier" options (plain cheerios, corn flakes, nut grapes, ...), nutritional yeast, ....), eating eggs?

You mentioned lactose intolerance, but since you aren't really bothered by it, I assume cheese and possibly yogurt are absolutely no problem.

I guess my question is why can't you. What is it about a natural b12 deficiency that makes it so the normal vegan or vegetarian options aren't sufficient?

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...

You listed two telltale signs of celiac disease: Low B12 Percieved Lactose Intolerance

I'm in the same boat, I resolved it with Nutritional Yeast.

I prefer Brewer's Yeast in a particular liquid form ;)

But I actually had to look up nutritional yeast as I hadn't heard of it here (Canada). It actually sounds like a promising supplement to my own diet. It seems like the only catch is that it doesn't produce B12 naturally, and I'll have to be sure to pick up the fortified version (unless they all are?)

No. They don't all have added B12. Add to popcorn.

How did you discover you had a deficiency?

Do a blood test. All vegetarians should do blood tests every now and then.

As an aside; I ate a vegan diet for 2-3 years and my B12 was fine. That’s not to say it would’ve been fine 2-3 years later, though.

Like the other commenter said— it was a blood test. The result was actually low hemoglobin. Low hemo unfortunately runs in the family as well– my mother has a severe case of anemia and suffers a range of issues related to that. Thankfully, I'm nowhere near that case.