Lettuce

Food · Vegetable · Food, Typed Supps

Nearly all water — but the darker the leaf, the more it actually gives you.

Stage by stage

Intake (Cell walls ruptured): Chewing tears open leaf cells — the rate-limiting step for releasing carotenoids.
Digestion (Fat-dependent solubilisation): Bile and dietary fat form micelles; without lipid in the meal the pigments are not absorbed.
Bloodstream (Carotenoids transported): Lutein, beta-carotene and vitamin K1 enter circulation on lipoproteins.
Eye (Macular pigment): Lutein is selectively deposited in the macula, building macular pigment over months.

Time to effect

Months: Macular pigment density responds to sustained lutein intake over roughly three to six months.

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, Keto, Low-FODMAP, Gluten-free.

In season

May to September in the northern hemisphere, November to March in the southern.

Satiety

The satiety index is measured on 240 kcal servings. At 17 kcal per 100 g that is 1.4 kg of this, which is not a serving anyone eats — so the index has nothing to say about it.

Environmental footprint

0.5 kg CO2e and 108 litres of freshwater per kg, matched to "Other vegetables" in Poore & Nemecek (2018), Science 360.

Cost band

Cheap — roughly £2.5 per kg, as a band midpoint rather than a price.

Key nutrients

Lutein
Folate
Potassium
Water

Nutrition per 100g

Calories: 17
Protein: 1.2g
Carbohydrate: 1.8g
of which sugars: 1.8g
Fat: 0.2g
of which saturated: 0g
Fibre: 1.8g
Sodium: 16mg

Food vs. supplement

Lutein capsules used in eye research are dosed around 10mg a day; 100g of cos gives roughly 1.1mg. Lettuce is not competing with that — its case is potassium, folate, fibre and pigments arriving together at almost no energy cost.

Kitchen tip

Keep the dark outer leaves — they hold most of the lutein, folate and vitamin K. Dry the leaves before dressing so the oil clings, and dress with something containing fat.

Common myth

"Lettuce has negative calories — you burn more digesting it than it contains." In reality: No food has a negative energy balance; digestion costs at most 20-30% of a food's energy. Lettuce is genuinely very low in energy at 17kcal per 100g, and the darker-leaved types carry real lutein, folate and potassium alongside that.