Benefits
Bowel regularity with two green kiwifruit a day
In a randomized crossover trial in three countries, adults with chronic constipation, including some with IBS-C, who ate two green kiwifruit a day for 4 weeks gained about 1.5 complete bowel movements a week. Fiber-matched psyllium reached that level only in the IBS-C group. Participants knew what they were eating, and the trial was funded mainly by a kiwifruit marketer.
Stool consistency, straining and bloating
In a US trial of 79 adults with chronic constipation, two green kiwifruit, 100 g of prunes or 12 g of psyllium a day for 4 weeks all raised weekly complete bowel movements, with similar responder rates. Kiwifruit also improved stool consistency, straining and bloating, caused the fewest side effects and left the fewest people dissatisfied. There was no placebo group.
Stool frequency and bowel water content in healthy adults
In 14 healthy volunteers, eating two kiwifruit twice a day for 3 days, compared with a maltodextrin control, increased water in the small bowel and colon volume on MRI scans, and stools became more frequent (about 1.5 versus 1.1 a day) and softer. The European Food Safety Authority found six human studies consistent on stool frequency with two to four green kiwifruit a day.
Bowel habits with kiwifruit powder or extract capsules
Capsule trials give mixed results. A green kiwifruit powder at 2,400 mg/day raised bowel movements in 19 healthy adults but not in 9 with constipation, and a 1 g/day extract did no better than placebo. In 186 adults with IBS-C, an extract improved bowel frequency, stool form and pain on separate measures but missed its main combined goal. A pooled review rated the extract evidence low certainty.
Protein digestion from the actinidin enzyme
Green kiwifruit contains actinidin, an enzyme that breaks down protein. In 12 healthy older adults, green kiwifruit eaten with a beef meal made the meal's amino acids reach the blood faster than gold kiwifruit, which lacks the enzyme, but the total absorbed and muscle protein measures did not differ. Faster stomach digestion of beef, gluten and soy protein has been shown in rats.
A whole-food source of vitamin C and fiber
By USDA figures, 100 g of raw green kiwifruit provides about 93 mg of vitamin C and 3 g of fiber, so the two-fruit portion used in bowel trials supplies roughly 185 mg of vitamin C and 6 g of fiber. These are nutrient amounts, not tested outcomes; what vitamin C itself does is covered on the vitamin C page.
Sleep quality when eaten before bed
The sleep evidence is preliminary. Two small studies with no control group, in 24 adults with sleep complaints and in 15 elite athletes, reported better sleep scores after 4 weeks of two kiwifruit an hour before bed. A single-blind crossover in 24 young men tested one evening only and found better morning alertness with dried kiwifruit versus water, with weaker trends for fresh fruit.
Mechanism of action
Fiber that holds water in the gut
Two green kiwifruit supply about 6 g of fiber. On MRI, kiwifruit raised the water content of the small bowel and ascending colon and increased colon volume, which fits the softer, more frequent stools seen in trials. Fiber is not the whole story: a fiber-matched psyllium dose did less in one trial.
Actinidin breaks down dietary protein
Actinidin is a cysteine protease found in green kiwifruit and largely absent from gold kiwifruit. In rats, green kiwifruit in the diet increased stomach digestion of beef, gluten and soy protein and sped gastric emptying for some proteins. In people, it sped amino acid appearance after a beef meal without raising the total absorbed.
Serotonin metabolism (sleep hypothesis)
In a one-night crossover, fresh and dried green kiwifruit both raised urinary 5-HIAA, a breakdown product of serotonin, compared with water. The authors proposed this as a possible link to the sleep and mood changes they saw; it has not been tested as a cause.
Clinical trials
Randomized, single-blinded, controlled crossover: 4 weeks of two green kiwifruit a day and 4 weeks of psyllium 7.5 g/day (matched at about 6 g fiber), separated by a 4-week washout; funded mainly by Zespri International (Gearry et al. 2023, Am J Gastroenterol)
184 adults in New Zealand, Italy and Japan: 63 healthy controls, 60 with functional constipation and 61 with IBS-C.
Kiwifruit raised complete spontaneous bowel movements by about 1.5 a week in both constipated groups (1.53 and 1.73) and improved GI symptom scores. Psyllium reached that level only in the IBS-C group, and in the pooled constipated groups kiwifruit did better than psyllium (P = 0.038). No significant adverse events. Participants knew which treatment they were eating.
Exploratory, partially randomized comparative-effectiveness trial: two green kiwifruit, 100 g prunes or 12 g psyllium a day for 4 weeks (Chey et al. 2021, Am J Gastroenterol)
79 US adults with chronic constipation and 3 or fewer complete bowel movements a week; 75 with complete data (29 kiwifruit, 24 prunes, 22 psyllium).
The share of responders on the primary endpoint was similar for all three foods, and all three increased weekly complete bowel movements. Kiwifruit and prunes improved stool consistency; all three reduced straining; kiwifruit improved bloating. Kiwifruit had the fewest adverse events and the fewest dissatisfied participants. No placebo arm.
Randomized, double-blind, placebo-controlled crossover; each of four treatments taken for 28 days with 14-day washouts (Ansell et al. 2015, Nutr Res)
19 healthy adults and 9 adults with functional constipation.
In healthy adults, Actazin green kiwifruit powder at 2,400 mg/day and a gold kiwifruit powder at 2,400 mg/day increased daily bowel movements compared with washout; stool form did not change. In the 9 constipated adults, no treatment differed from placebo. Small groups, and powder doses hold far less fruit than two kiwifruit.
Multicenter, randomized, double-blind, placebo-controlled parallel trial of 575 mg extract twice daily for 4 weeks then once daily for 4 weeks; funded by Vital Food Processors (Holtmann et al. 2025, JGH Open)
186 adults with constipation-predominant irritable bowel syndrome (Rome III).
The combined primary endpoint (more complete bowel movements plus at least 30% less pain) was not met: 24% vs 26% on placebo. On separate measures, more people on the extract had more frequent bowel movements (54% vs 36%), better stool form (87% vs 73%) and less pain (74% vs 59%). Fewer reported adverse events (67% vs 81%).
Randomized, double-blind crossover; two kiwifruit a day for 14 days and again with 100 g ground beef during each test day (Park et al. 2021, Eur J Nutr)
12 healthy older adults (6 men, 6 women).
With green kiwifruit, which contains actinidin, blood essential amino acids rose faster after the beef meal than with gold kiwifruit, which lacks it. The total amount of amino acids absorbed did not differ, and there were no differences in muscle or whole-body protein metabolism.
Randomized, single-blind crossover with a water control; each treatment taken once with a standard evening meal (Kanon et al. 2023, Front Nutr)
24 healthy young men, 12 with poor and 12 with good sleep quality.
Dried kiwifruit powder (with skin) improved morning sleepiness, alertness on waking and vigor versus water; fresh fruit's sleep and mood changes were trends that did not reach significance. Both raised urinary 5-HIAA, a serotonin metabolite. Single-night effects in men only; it did not test regular use.
Uncontrolled, self-controlled before-and-after study: two kiwifruit 1 hour before bedtime nightly for 4 weeks (Lin et al. 2011, Asia Pac J Clin Nutr)
24 adults aged 20 to 55 with self-reported sleep problems (22 women).
Compared with their own baseline, questionnaire sleep scores improved, time to fall asleep and waking after sleep onset fell, and total sleep time and sleep efficiency rose on a wrist activity monitor. With no placebo or comparison group, expectation and time effects cannot be ruled out.