Green Tea

Food · Drink · Food, Typed Supps

The calm-alert combination is real. The fat burning is a rounding error.

Stage by stage

Tannins (Gut lumen): Galloylated catechins bind non-haem iron from the same meal before it can be absorbed.
Caffeine (Circulation): About 13 mg per 100 g — a third of coffee’s concentration — reaches the brain within half an hour.
Theanine (Cortex): L-theanine increases alpha-wave activity and blunts the jittery edge of the caffeine.
Catechins (Liver): EGCG is rapidly conjugated and cleared, so systemic exposure from the drink stays very low.

What the evidence supports

Improving alertness and attention-switching — moderate evidence. The caffeine–L-theanine combination is one of the better-replicated cognitive findings in nutrition, consistently outperforming caffeine alone on attention tasks.
Burning fat or aiding weight loss — insufficient evidence. Pooled trials put the rise in energy expenditure near 4% and weight differences in fractions of a kilogram over months — inside ordinary day-to-day variation.
Evidence that it causes Liver injury from the brewed drink — insufficient evidence. Reassuring for tea itself. EFSA identified a hepatotoxicity signal for concentrated catechin supplements at and above 800 mg EGCG daily; no comparable signal exists for the infusion.

Timing

Away from meals if iron status matters — the tannin interaction is with the food in the stomach, not with the tea itself. Caffeine is a third of coffee’s, but still enough to matter after mid-afternoon for sensitive people.

Time to effect

30–45 min: Caffeine and theanine effects peak together.
Weeks–months: Any cardiovascular association is from habitual intake, and observational.

Allergens

None of the fourteen major allergens. Derived from what this food is, not from a product label.

Eating patterns

Fits: Vegan, Vegetarian, Pescatarian, Halal, Kosher, Gluten-free. Depends on the product: Keto, Low-FODMAP.

Satiety

Not scored: the satiety index is measured on 240 kcal servings, and nobody eats a 240 kcal serving of this. The question does not apply rather than the answer being unknown.

Cost band

Pricey — roughly £30 per kg, as a band midpoint rather than a price.

Key nutrients

Nutrition per 100g

Calories: 1
Protein: 0.2g
Sodium: 1mg

Food vs. supplement

This is the clearest food-versus-supplement split in the tea literature. Brewed green tea has an unblemished safety record at ordinary intakes; concentrated catechin extracts have a documented hepatotoxicity signal, which is why several regulators now require a warning on the capsule and none on the teabag.

Kitchen tip

Around 80 °C and two to three minutes. Boiling water and long steeping both push the extraction toward tannin, which makes the cup bitter and the iron interaction worse at the same time.

Common myth

“Green tea burns fat.” In reality: The effect exists and is tiny. Pooled trials put the increase in energy expenditure at roughly 4%, and weight-loss trials find differences measured in fractions of a kilogram over months — well inside the noise of ordinary day-to-day variation. Drink it because the caffeine–theanine combination is genuinely pleasant to work under, not as a weight strategy.