Coffee

Food · Drink · Food, Typed Supps

The most widely used stimulant on earth, and one of the best studied.

Stage by stage

Intake (Oral, rapid): Caffeine is absorbed nearly completely, with plasma levels peaking in 30–60 minutes.
Central action (Adenosine receptors): It competitively blocks adenosine A1 and A2A receptors, suppressing the perception of accumulated fatigue.
Circulation (Systemic): Modest, transient rises in blood pressure and catecholamines follow, attenuating with habitual use.
Clearance (Liver, CYP1A2): Metabolised chiefly by CYP1A2, with a half-life of roughly 4–6 hours that varies severalfold between people.

Timing

Morning to early afternoon. With a 4–6 hour half-life, mid-afternoon intake commonly still impairs sleep onset and reduces deep sleep even in people who report falling asleep fine.

Time to effect

30–60 min: Subjective alertness rises with plasma concentration.
Days–wks: Tolerance to the blood-pressure and some alertness effects develops with regular use.

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.

Environmental footprint

28.5 kg CO2e and 1571 litres of freshwater per kg, matched to "Coffee" in Poore & Nemecek (2018), Science 360.

Cost band

Pricey — roughly £20 per kg, as a band midpoint rather than a price.

Key nutrients

Nutrition per 100g

Calories: 10
Protein: 1.7g
Fat: 0.3g
of which saturated: 0.1g
Sodium: 2mg

Food vs. supplement

Brewed coffee and anhydrous caffeine are pharmacologically equivalent at matched dose. Coffee adds chlorogenic acids and — in unfiltered preparations — the LDL-raising diterpenes a capsule does not contain.

Kitchen tip

Unfiltered brews (French press, percolator, Turkish) retain the LDL-raising diterpenes cafestol and kahweol that paper filters remove.

Common myth

“Coffee gives you energy.” In reality: It supplies no usable energy. It blocks the adenosine signal that reports tiredness, so fatigue is masked rather than resolved — and the accumulated sleep pressure is still there when it clears.