Iceberg Lettuce

Food · Vegetable · Food, Typed Supps

Iceberg lettuce isn't "just crunchy water" - it's mostly water, but that water comes packaged with real vitamin K.

Stage by stage

Crunch & Hydrate (Mouth): Chewing ruptures iceberg lettuce's water-filled cells, releasing fluid from a vegetable that is about 95-96% water by weight, along with its characteristic crunch.
Fast Digestion (Stomach): Because it's low in fiber, fat, and protein compared to most vegetables, iceberg lettuce moves through the stomach quickly with minimal digestive breakdown required.
Vitamin Absorption (Small Intestine): In the small intestine, fat-soluble vitamin K and provitamin-A carotenoids are absorbed, with absorption improved significantly when the lettuce is eaten alongside a source of dietary fat such as salad dressing.
Clotting & Bone Support (Liver & Bone): Absorbed vitamin K reaches the liver, where it activates blood-clotting factors, and bone tissue, where it helps carboxylate proteins involved in bone mineralisation.

Timing

Vitamin K and vitamin A precursors in iceberg lettuce are fat-soluble, so eating it alongside a source of fat (dressing, nuts, cheese, avocado) improves how much of those vitamins your body actually absorbs.

Time to effect

Days to weeks: There is no acute effect from a single serving; iceberg lettuce's contribution to vitamin K status, clotting-factor function, and bone health builds gradually with consistent intake over days to weeks.

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 14 kcal per 100 g that is 1.7 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

Nutrition per 100g

Calories: 14.3
Protein: 1g
Carbohydrate: 2.1g
of which sugars: 2.1g
Fat: 0g
of which saturated: 0g
Fibre: 1.1g
Sodium: 12mg

Food vs. supplement

Iceberg lettuce is a poor source of concentrated nutrients compared to a vitamin K or multivitamin supplement, but it contributes hydration, volume, and a very low-calorie base to a meal that a supplement pill cannot replicate.

Kitchen tip

Store iceberg lettuce whole and unwashed, tear rather than knife-cut it to reduce browning at cut edges, and dress it with an oil-based dressing to help absorb its fat-soluble vitamin A and vitamin K.

Common myth

"Iceberg lettuce has no nutritional value - it's basically just crunchy water." In reality: Iceberg lettuce is genuinely lower in nutrient density than darker lettuces like romaine or spinach, but USDA data show a 100 g serving still provides about 24 µg of vitamin K (roughly 20% DV) plus folate, potassium, and some vitamin A - modest nutrition in a very high-water, low-calorie package, not zero nutrition.