Soy Beverage

Food · Drink · Food, Typed Supps

The thing worth checking on the carton is whether calcium has been added. Unfortified soy milk has almost none.

Stage by stage

Intake (Thin liquid): Ground soybean extract in water leaves the stomach quickly, with a little fibre from the bean carried through.
Absorption (Protein and calcium taken up): Amino acids and any added calcium are absorbed from the small intestine; the calcium fortificant must be suspended to be present at all.
Muscle (Near-complete plant protein): Soy protein supplies all the essential amino acids, unusual among plant milks, at a concentration close to dairy.
Skeleton (Only if fortified): Fortified cartons deliver calcium at close to dairy levels; the unfortified version contributes almost none.

Time to effect

Immediate to years: The switch to a fortified carton changes calcium and B12 intake from the first glass; skeletal outcomes accrue over years.

Allergens

Contains: Soya. Derived from what this food is, not from a product label.

Eating patterns

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

1 kg CO2e and 28 litres of freshwater per kg, matched to "Soy milk" in Poore & Nemecek (2018), Science 360.

Cost band

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

Key nutrients

Plant protein
Added calcium
Added B12 and riboflavin (fortified versions)

Nutrition per 100g

Calories: 59
Protein: 3.7g
Carbohydrate: 4.6g
of which sugars: 2.6g
Fat: 2.7g
of which saturated: 0.4g
Fibre: 0.6g
Sodium: 44mg

Food vs. supplement

A fortified glass and a calcium tablet supply comparable calcium, but the glass also brings 3.7g of complete protein, potassium, magnesium and, in the fully fortified versions, riboflavin and B12 — the specific nutrients someone leaving dairy is most likely to lose. A tablet fixes one line of that list.

Kitchen tip

Shake the carton hard before every pour, not just the first. The calcium is suspended, not dissolved, and the last glass from an unshaken carton can be meaningfully richer than the first — which also means the earlier glasses were poorer.

Common myth

“Soy milk is basically milk with the same nutrition.” In reality: Only the fortified versions come close, and they come close because calcium and vitamins were deliberately added. The protein is genuinely comparable without any help; everything else on the panel is a formulation choice.