Lemon Juice

Food · Drink · Food, Typed Supps

Too small a serve to feed you. Big enough to change what your gut absorbs.

Stage by stage

Acid (Enamel): At pH around 2.3, neat lemon juice sipped habitually is genuinely erosive.
Reduction (Stomach): Ascorbate converts ferric iron to the ferrous form the gut transporter accepts.
Iron uptake (Duodenum): A soluble ascorbate–iron chelate survives the pH rise that would otherwise precipitate it.
No pH shift (Circulation): Blood pH is held constant by kidneys and lungs; nothing you drink moves it.

Timing

Strictly with the meal. Taken separately it does nothing for iron, because the effect happens in the gut alongside the food.

Time to effect

That meal: The iron absorption effect, and only for the meal it is eaten with.
Years: Enamel erosion, if neat lemon juice or lemon water is sipped habitually.

Allergens

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

Eating patterns

Fits: Vegan, Vegetarian, Pescatarian, Halal, Kosher, Keto, Low-FODMAP, Gluten-free.

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

0.4 kg CO2e and 83 litres of freshwater per kg, matched to "Citrus fruit" in Poore & Nemecek (2018), Science 360.

Cost band

Cheap — roughly £2 per kg, as a band midpoint rather than a price.

Key nutrients

Vitamin C
Citric acid

Nutrition per 100g

Calories: 27
Protein: 0.6g
Carbohydrate: 1.8g
of which sugars: 1.8g
Fat: 0.1g
Fibre: 2g
Sodium: 3mg

Food vs. supplement

This is the clearest everyday example of a food acting like a supplement. A squeeze of lemon on a lentil dish does for that meal’s iron roughly what taking vitamin C with an iron tablet does — which is why the advice appears in dietetic guidance for plant-based diets.

Kitchen tip

Squeeze it over the food, not into a glass an hour earlier. The whole effect is on the iron sitting on that plate.

Common myth

“Lemon water alkalises the body.” In reality: It cannot. Blood pH sits between 7.35 and 7.45 and is defended by the kidneys and lungs; food does not move it, and if anything did you would be seriously unwell. Urine pH does change with diet, which is what people are seeing, and that is the kidney working correctly rather than a systemic shift. Lemon juice does something genuinely useful — it multiplies iron absorption from the meal — which is a better reason to use it.