B Vitamins and B12: When Food Is Not Enough
Good news: a low-carbohydrate plate is the best source of B vitamins there is. Meat, liver, eggs, fish, and leafy greens provide everything from B1 to B12 without supplements. The bad news: there are four situations when B12 is not absorbed even from perfect food, and its deficiency can look like “age” and “fatigue” for years. Section — vitamins and minerals.
What B vitamins do
Energy from food — B1, B2, B3, B5. Protein and hormones — B6. Blood and DNA — B9 (folate) and B12. Nerves — B12 and B1. With sugar and flour, B1 and B3 are used up processing carbohydrates; without them, the need decreases. Folate comes from leafy greens and liver, not from “fortified flour,” which is not part of the method and is not needed.
Four situations when B12 is insufficient
Metformin: reduces B12 absorption in 10-30% of users, with the effect increasing over years of use. Omeprazole and other acid blockers: without acid, B12 cannot be separated from food protein. Being over 50: stomach acidity naturally decreases, and up to one-third of people over 60 are deficient. Vegetarianism: plants contain no B12 at all. In addition, there are stomach and intestinal surgeries and autoimmune gastritis. If at least one applies, testing is mandatory.
Signs of B12 deficiency
- Fatigue that does not go away after sleep
- Numbness and tingling in the fingers
- Forgetfulness, brain fog
- Shortness of breath, pallor, palpitations
- A smooth, red, burning tongue
- Low mood for no reason
Tests and normal ranges
| Test | Normal range | What the result means |
|---|---|---|
| Blood B12 | above 400 pg/ml | 200-400 — gray zone, homocysteine is needed; below 200 — deficiency |
| Homocysteine | up to 10 µmol/l | above — functional B12 or folate deficiency |
| Folate | above 4 ng/ml | rarely low with leafy greens on the plate |
| Complete blood count | MCV up to 100 | large red blood cells — a late sign of B12 deficiency |
Dosage and form
With confirmed deficiency — methylcobalamin or cyanocobalamin 1000 mcg daily under the tongue or as a tablet; with severe deficiency and absorption problems — injections as prescribed by a doctor. Methylcobalamin is not “better,” it is simply more expensive; for most people, cyanocobalamin works just as well. For prevention when taking metformin and after 50 — 250-500 mcg daily. From food: 100 g of liver covers a week’s requirement, while meat and fish daily cover the daily requirement. About the thyroid, which can mimic the same symptoms — the thyroid gland and weight.
Frequently asked questions
Does a B-complex “for energy” make sense?
No, if you eat meat and leafy greens. Sleep, electrolytes, and the thyroid provide energy, not a B-complex. Excess B vitamins leave the body in urine — hence its yellow color after a tablet.
I take metformin. What should I do?
B12 and homocysteine once a year. If levels decline — 500-1000 mcg daily continuously. This is a standard recommendation, not “just in case.”
How long should I wait for an effect?
Fatigue and brain fog — 2-4 weeks. Numbness — 2-3 months, sometimes longer if the deficiency lasted a long time.
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Reviewed by Anastasia Zhukova, Fitness Trainer • Author of a Nutrition and Training System • Creator of an AI Personal Support Platform
A human has reviewed this material against the method and real client practice.