Vitamin B1 — Thiamin

Thiamin’s main job is helping the body convert food — particularly carbohydrates — into usable energy. It’s one of the B vitamins that sits at the foundation of your metabolism, and without enough of it, that conversion process doesn’t work properly. The result is fatigue, weakness, and over time, effects on the nervous system that go well beyond just feeling tired.

Outright thiamin deficiency is uncommon for most people eating a reasonably varied diet. It becomes a real concern in two specific contexts: diets built heavily around polished white rice with little else — historically the cause of a deficiency disease called beriberi — and chronic heavy alcohol use, which both blocks thiamin absorption and depletes whatever stores the body has. Outside of those situations, getting enough thiamin through food isn’t difficult.

Whole grains, legumes, and pork are the richest sources. Fortified cereals and breads also contribute meaningfully, which is partly why thiamin deficiency is less common in populations that eat a lot of processed grain products — the thiamin that’s removed during processing gets added back in. Whole food sources are still the better choice, but the fortification is worth knowing about.

Because thiamin is water-soluble, the body doesn’t hold onto it. It needs to show up in your diet regularly.

Reference Card

Vitamin type: Water-soluble Pillar: Nourish

What it does for you

Helps convert carbohydrates into energy your body can actually use
Supports nervous system function
Keeps muscles and the heart working properly

Where to get it

Pork, trout, black beans, lentils, edamame, whole grains, fortified cereals and breads

Considerations

Water-soluble — not stored in the body; needs to come from food regularly
Alcohol significantly impairs absorption and depletes stores — a meaningful concern for people who drink heavily
Cooking degrades thiamin somewhat; heavily processed foods lose it and have it added back through fortification

Signs your intake might be low

Persistent fatigue and low energy
Muscle weakness
Numbness or tingling, particularly in the hands and feet

Common myths

Thiamin deficiency is only a problem in developing countries — chronic alcohol dependence is a significant cause of deficiency across all populations
Enriched white rice and whole grain rice are nutritionally equivalent — enriched rice has thiamin added back, but whole grains retain it naturally alongside other nutrients that don’t get replaced