Does Prune Juice Help Constipation? How Much, How Fast

Yes, in the trials. Dried prunes at 100 g a day (8 to 12 prunes) gave 3.5 complete bowel movements a week against 2.8 on 22 g of psyllium over three weeks in 40 adults with chronic constipation, and 80 to 120 g a day raised daily stool weight by 22 to 33 g in 120 UK adults over four weeks.^{1, 2, 3} Prune juice has one placebo-controlled trial: 54 g a day for eight weeks in 84 Japanese adults with chronic constipation reduced hard, lumpy stools within three weeks and increased normal stools without increasing loose or watery ones.⁴ The two are not the same food. In Great Britain "Dried plums/prunes contribute to normal bowel function" is an authorised claim on condition of 100 g of dried plums a day; prune juice has no authorised claim of its own; commercial juice carries only trace fibre, and the trial juice contained pectin.^{4, 5, 6} For the 30 g a day the rest of the diet should supply, see the Wellgard fibre guide.

What did the trials find?

In the 2011 crossover trial, 40 adults with chronic constipation ate 50 g of dried plums twice a day for three weeks, then took 11 g of psyllium twice a day, the same 6 g of fibre; complete spontaneous bowel movements and stool consistency were better on prunes, straining was no different, and both were equally well tolerated.¹ In the 2019 UK trial, 120 adults with low fibre intakes and three to six stools a week ate 80 g or 120 g of prunes a day with 300 ml of water, or drank the water alone, for four weeks: stool weight rose by 22 g a day on 80 g and 33 g on 120 g against a 1 g fall on water, frequency rose, transit time did not change and flatulence was higher.² In a 2021 US trial of 79 adults, 100 g of prunes a day, two green kiwifruit a day and 12 g of psyllium a day all raised complete bowel movements over four weeks; prunes were tolerated better than psyllium but less well than kiwi.⁷

The juice trial is the 2022 Japanese study: 84 adults with chronic constipation drank 54 g a day of prune juice or a placebo drink for eight weeks. Hard, lumpy stools fell below the placebo group's by week three, normal stools rose, loose stools did not, and there were no adverse events; the trial was partly funded by the juice's manufacturer.⁴ A 2024 meta-analysis pooling the two prune trials found prunes no different from psyllium for stool frequency.⁸

How much prune juice should you drink, and how fast does it work?

No trial has set one volume against another. The juice trial used 54 g a day, a little over 50 ml, and measured change over weeks.⁴ The NHS asks everyone to keep fruit juice to a combined 150 ml a day because its sugars count as free sugars, so a sensible first dose is a small 150 ml glass, once, with a day's wait before deciding whether you need it again.⁹ Drink water alongside: the UK prune trial gave 300 ml of water a day with the fruit.²

On time of day there is no evidence either way: morning or evening, warm or cold, the sorbitol is the same, and warming only makes it pleasanter. People who fear urgency take it in the morning rather than last thing at night. The juice trial saw stool form shift within three weeks.⁴

What in prune juice explains the trial result?

The authors suggest sorbitol could explain it, with the juice's pectin and polyphenols alongside.⁴ Prunes contain 5.2 g of fibre per 100 g by the UK food tables and about 14.7 g of sorbitol, a sugar alcohol that is poorly absorbed, holds water in the gut and is fermented by colon bacteria, plus chlorogenic acids; prune juice is the fruit filtered, with about 6 g of sorbitol per 100 g, and the UK food tables put commercial juice at trace fibre and 14.4 g of sugars per 100 g.^{6, 10} The register's claim attaches to 100 g of the dried fruit, the amount the trials used. The wind some people get is the sorbitol fermenting, and anyone with IBS who reacts to sorbitol in sugar-free sweets will usually react to prune juice too.⁶

What does each give you, and how many prunes make a glass?

Prunes carry fibre, sorbitol, phenolics and potassium, were tested against psyllium in two trials and hold the register's wording at 100 g a day; the juice carries sorbitol, phenolics and potassium with trace fibre, has the one placebo-controlled trial, and suits someone who will not eat 8 to 12 prunes a day.^{1, 4, 5, 7} Three prunes a day, the most common figure online, is about 30 g, under a third of the trial dose; the 50 g (five or six prunes) that preserved hip bone density over a year in 235 post-menopausal women was never tested for bowel effect.¹¹ Nobody can tell you how many prunes equal a glass of juice: juicing removes the fibre and sorbitol varies between products. A 100 g portion of prunes also brings 36.5 g of sugars and 149 kcal.¹⁰ Is prune juice good for you goes through the sugar and potassium in detail.

What about a prune juice concentrate?

A concentrate is prune juice with most of its water removed, diluted back at home. One 30 ml serving of a prune concentrate, mixed into a glass of water once a day, supplies a few hundred milligrams of potassium, and potassium contributes to normal muscle function; labels typically warn that it may have a laxative effect and that it is not for children under 12, that it has no added sugar but carries the fruit's own, and that once opened it is kept in the fridge. The register's bowel-function claim belongs to 100 g of dried plums, and no dried-plum figure exists for a concentrate serving. Anyone with IBS who is sorbitol-sensitive, anyone with diabetes counting fruit sugars, and anyone on a potassium-restricted diet for kidney disease or taking potassium-sparing medicines should ask their GP or dietitian first.¹² No trial has compared a concentrate with pressed juice or whole prunes.

Is prune juice better than a laxative, and when should you see a GP?

No trial has compared prune juice with any laxative. The nearest comparison is prunes against psyllium, where prunes did as well or better, and a pharmacy sachet of ispaghula husk is a licensed bulk-forming laxative rather than a food.^{1, 7} The NHS order is food and fluid first (it lists fruits containing sorbitol), fibre built up gradually, movement, a routine and a footstool, then a pharmacist conversation; our constipation guide sets out those steps, and what psyllium husk does covers the 10 to 12 g a day the psyllium trials used.¹³ See a GP, the NHS says, if constipation is not improving with treatment, if you are regularly constipated or bloated, if there is blood in your poo, if you have lost weight without trying, or if you feel tired all the time; a sudden change in bowel habit is a GP appointment, not a glass of juice.¹³ Several days with no movement plus severe pain, bloating or vomiting is urgent: call NHS 111. Babies and children are a separate case: the NHS gives age-specific advice, a constipated baby is a health visitor or GP conversation, and no juice dose is given here.¹⁴

Frequently asked questions

Does prune juice soften stool that is already hard?

In the one trial it did, over weeks: hard, lumpy stools fell below placebo levels by week three on 54 g a day.⁴ Stool that has been hard for days with nothing passing can be impaction, which a GP or pharmacist needs to clear first.¹³

What is the "nurse's cocktail" for constipation?

A hospital mixture of prune juice, apple sauce and bran. No trial has tested the mix. Prune juice has the eight-week trial above, and the register authorises "Wheat bran fibre contributes to an acceleration of intestinal transit" at 10 g of wheat bran fibre a day.^{4, 5}

Should you drink water after prunes or prune juice?

Yes. The UK trial gave 300 ml of water a day with the prunes.²

Is there anything better than prune juice for constipation?

Two green kiwifruit a day did as well as 100 g of prunes or 12 g of psyllium in the head-to-head trial and were the best tolerated.⁷ Which foods are high in fibre has the portions.

How many prunes are too many?

The trials went to 120 g (about 12) with more wind and no other harm; loose stools mean you have passed your sorbitol threshold.²

Sources

1. Attaluri A, et al. Randomised clinical trial: dried plums (prunes) vs. psyllium for constipation. Alimentary Pharmacology and Therapeutics, 2011. PubMed 21323688.
2. Lever E, et al. The effect of prunes on stool output, gut transit time and gastrointestinal microbiota: a randomised controlled trial. Clinical Nutrition, 2019. PubMed 29398337.
3. Lever E, et al. Systematic review: the effect of prunes on gastrointestinal function. Alimentary Pharmacology and Therapeutics, 2014. PubMed 25109788.
4. Koyama T, et al. Prune juice containing sorbitol, pectin, and polyphenol ameliorates subjective complaints and hard feces while normalizing stool in chronic constipation: a randomized placebo-controlled trial. American Journal of Gastroenterology, 2022. PubMed 35971232.
5. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. gov.uk.
6. Stacewicz-Sapuntzakis M, et al. Chemical composition and potential health effects of prunes: a functional food? Critical Reviews in Food Science and Nutrition, 2001. PubMed 11401245.
7. Chey SW, et al. Exploratory comparative effectiveness trial of green kiwifruit, psyllium, or prunes in US patients with chronic constipation. American Journal of Gastroenterology, 2021. PubMed 34074830.
8. van der Schoot A, et al. Systematic review and meta-analysis: foods, drinks and diets and their effect on chronic constipation in adults. Alimentary Pharmacology and Therapeutics, 2024. PubMed 37905980.
9. NHS. Sugar: the facts. nhs.uk.
10. Public Health England. McCance and Widdowson's Composition of Foods Integrated Dataset (CoFID), 2021. gov.uk.
11. De Souza MJ, et al. Prunes preserve hip bone mineral density in a 12-month randomized controlled trial in postmenopausal women: the Prune Study. American Journal of Clinical Nutrition, 2022. PubMed 35798020.
12. NHS. Chronic kidney disease: living with. nhs.uk.
13. NHS. Constipation. nhs.uk.
14. NHS. Constipation in children. nhs.uk.