Prune

Food · Fruit · Food, Typed Supps

A dried plum with a real, well-tested effect on constipation — and a good reason not to eat the whole packet.

Stage by stage

Intake (Concentrated by drying): Drying removes about three-quarters of the plum's water, concentrating sugar, fibre and potassium.
Small intestine (Sorbitol poorly absorbed): Sorbitol is absorbed slowly and incompletely, so much of it passes onward.
Large intestine (Osmotic water influx): Unabsorbed sorbitol draws water into the bowel while fibre adds bulk and is fermented.
Longer term (Bone and blood pressure): 715mg potassium per 100g supports blood pressure; trials on bone density are promising but unsettled.

Time to effect

Days: Effects on stool frequency and consistency typically appear within one to three days of daily intake.

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.

Satiety

155 on the satiety index, where white bread is 100 — high. Modelled from the Holt et al. (1995) measurements.

Environmental footprint

1.1 kg CO2e and 199 litres of freshwater per kg, matched to "Other fruit" in Poore & Nemecek (2018), Science 360.

Cost band

Cheap — roughly £3 per kg, as a band midpoint rather than a price.

Key nutrients

Dietary fibre
Sorbitol
Potassium
Vitamin K

Nutrition per 100g

Calories: 207
Protein: 2.6g
Carbohydrate: 45g
of which sugars: 31g
Fat: 0.4g
of which saturated: 0g
Fibre: 7.7g
Sodium: 4mg

Food vs. supplement

Prunes have matched or beaten psyllium in randomised trials for chronic constipation, and bring potassium, vitamin K and polyphenols that a fibre sachet does not. The separate bone-density claim rests on small trials and should be treated as promising rather than proven.

Kitchen tip

Soak in hot water or tea to soften. Start at five or six a day rather than a large handful, and drink fluid alongside — fibre without water can worsen constipation.

Common myth

"Prunes work because they are high in fibre." In reality: Fibre is only part of it. Sorbitol, a poorly absorbed sugar alcohol, draws water into the bowel osmotically and accounts for much of the effect — which is why strained prune juice still works, and why people sensitive to sorbitol react badly to a food sold to them as simply high-fibre.