...Sorry for the late response.
not a way to be sure. However, you have reduced B12-rich foods in your diet
including red meat and dairy. Other foods you could consider are fish such
as mackerel and salmon, and shellfish. Many foods such as breakfast cereals
are B12-fortified, so look for that on the label as well.
Other causes for B12 deficiency include medical conditions and medication.
egg and milk will help too
It's quite possible that the recent diet changes you've made contributed to a mild B12 deficiency. You can add dark green leafy vegetables to your diet such as spinach and kale as well as use a vitamin supplement daily.
Hope this reassures you.
So in answer to your question, yes, it is probably your diet which is causing you to be deficient in B-12. Vitamin B-12, and sometimes vitamin D (for people who don't get much sunshine) are pretty much the only supplements I recommend. Vitamin B-12 is not made by plants. It is not made by animals either, but is present in meat because animals harbor the bacteria which actually manufacture vitamin B-12. Hundreds of years ago, when our food wasn't so sterilized and was contaminated with a certain amount of bacteria from the soil, we didn't need supplemental B-12, but now we do.
I understand your reluctance to take supplements, but B-12 deficiency is a serious issue, so I strongly urge you to take a supplement in this case.
You may have had surgery to remove part of the stomach or the last part of your small intestine, called the ileum. This includes some types of surgery used to help very overweight people lose weight.
You may have problems with the way your body digests food, such as sprue (also called celiac disease), Crohn's disease, bacteria growth in the small intestine, or a parasite.This anemia can also happen if you don't eat enough foods with B12, but this is rare. People who eat a vegan diet and older adults who don't eat a variety of foods may need to take a daily vitamin pill to get enough B12. Other causes include drinking alcohol and taking some prescription and nonprescription medicines.