Kiwifruit

What it is

Kiwifruit come from the Actinidia genus. Green kiwifruit is Actinidia deliciosa [1], and gold-fleshed kiwifruit is Actinidia chinensis [2]. Some products use a kiwifruit extract containing the enzyme actinidin [3].

How it might work

Proposed mechanism: kiwifruit may draw water into the small bowel and ascending colon, increasing stool volume. In 14 healthy volunteers over three days, kiwifruit increased small-bowel water and colon volume and stool frequency compared with a control drink [4].

What the research says

A 2024 review of 23 studies found kiwifruit increased stool frequency more than psyllium, by about 0.36 bowel movements a week [5]. A 2022 review of 11 fruit trials found kiwifruit increased stool frequency more than palm date or orange juice [6]. Compared with psyllium, the 2022 review rated the kiwifruit effect on weekly bowel movements as moderate certainty, with a range that included no difference [7].

In a 2023 trial of 184 people, two green kiwifruit a day raised complete bowel movements by about 1.5 a week in functional constipation and 1.7 in IBS-C, from baseline [8]. A 2019 crossover trial of 32 people found three gold kiwifruit a day raised complete bowel movements from 3.3 to 6.3 a week, against 4.5 on psyllium [2]. In a 2020 study, whole kiwifruit reduced constipation and IBS pain scores in 38 people, 19 with IBS-C [9].

Abdominal pain improved in the 2022 review, rated moderate certainty [7]. A 2018 trial of 58 people found the extract reduced abdominal pain and painful defecation compared with placebo [3].

Extracts and supplements are less consistent. A 2023 review of 8 trials found kiwifruit supplements did not change stool frequency [10]. A 2015 crossover trial of 32 adults found 1 gram a day of extract did not change bowel movements [1]. A 2015 trial in healthy adults found two kiwifruit extracts increased bowel movements, but the constipated group of nine was too small to show a clear change [11].

Doses used in studies

Trials used two green kiwifruit a day for 4 weeks [8], three gold kiwifruit a day for 4 weeks [2], and 1 gram a day of freeze-dried extract for 3 weeks per period [1]. These are study doses, not recommendations.

Safety and interactions

Side effects: the 2023 trial reported no significant adverse events [8]. A 2018 extract trial reported no side effects, including diarrhoea, urgency or abdominal pain [3]. In a 2022 review, minor adverse events with encapsulated extract were not clearly higher than placebo, with a wide range [7].

No data were found in the studies reviewed on kiwifruit allergy, upper intake limits, medicine interactions, or use in pregnancy and breastfeeding. Trials included healthy adults, people with functional constipation and people with IBS-C [8]. People on other medicines, or those with allergies or digestive conditions, should ask a doctor first.

Caveats and open questions

The best evidence is for whole fruit, not extracts or capsules [10]. Most trials are small and short, and the longest ran about four months in total [2]. Some trials were funded by kiwifruit companies, and the 2023 trial was co-funded by Zespri International [8]. The 2022 review rated the overall evidence as low certainty, and called for large, rigorous trials [7].