When people talk about superfoods, they usually mean something rare and expensive: an Amazonian berry, a Himalayan powder, a seaweed from a far-off coast. But one of the best-studied “superfoods” for everyday health costs less than a dollar and is probably sitting in your local grocery store right now.
Meet the kiwifruit. Small, fuzzy, and often overlooked, it has quietly built an impressive scientific record, especially for something many people struggle with but rarely talk about: constipation.
Key Takeaways
- One green kiwifruit provides more vitamin C than an orange, plus fiber, potassium, and vitamin K.
- In a 2023 trial across New Zealand, Japan, and Italy, eating two green kiwis a day improved bowel movements more than a standard psyllium fiber supplement.
- In 2025, British dietitians published the first evidence-based dietary guidelines for chronic constipation, and kiwifruit made the list.
- Kiwi’s benefits likely come from a combination of water-holding fiber, a natural enzyme called actinidin, and gentle effects on gut movement.
- Kiwi allergy is relatively common, so it is not right for everyone.
A Nutrition Powerhouse in a Small Package
Originally from China, where it was known as the Chinese gooseberry, the kiwifruit was renamed in the 20th century by New Zealand growers after their national bird. Nutritionally, it punches far above its size:
- Vitamin C: One medium green kiwi supplies roughly 60 to 70 mg, more than many people’s full daily requirement and more than a typical orange.
- Fiber: About 2 to 3 grams per fruit, a mix of soluble and insoluble types.
- Vitamin K, vitamin E, folate, and potassium.
- Low calories: About 40 to 50 calories each.
The Kiwi vs. Psyllium Trial
Researchers led by Professor Richard Gearry of the University of Otago in New Zealand enrolled adults with functional constipation or constipation-predominant irritable bowel syndrome (IBS-C) in New Zealand, Japan, and Italy. In a crossover design, each person tried two treatments for four weeks each, separated by a break:
- Two green kiwifruit a day, peeled
- 7.5 grams of psyllium a day, a widely recommended fiber supplement
Extra Complete Bowel Movements per Week
| Group | Kiwifruit | Psyllium |
|---|---|---|
| All constipated participants | +1.69 | +0.90 |
| Functional constipation | +1.53 | +0.67 |
| IBS with constipation | +1.73 | +1.25 |
Source: Gearry et al., American Journal of Gastroenterology, 2023.
Participants also reported less abdominal discomfort while eating kiwis than while taking psyllium. A few caveats: the study was funded by Zespri, a kiwifruit marketer; participants knew which treatment they were getting; and most had relatively mild constipation. Still, it adds to several earlier studies with similar results.
Official Recognition
In October 2025, a team led by Dr. Eirini Dimidi and Professor Kevin Whelan at King’s College London published the first evidence-based dietary guidelines for managing chronic constipation in adults, endorsed by the British Dietetic Association. After reviewing more than 75 clinical trials, they recommended several specific foods and supplements, including:
- Kiwifruit
- Rye bread
- Mineral water high in magnesium
- Psyllium fiber supplements
- Certain probiotic strains
- Magnesium oxide supplements
Interestingly, the panel found that generic advice to “eat a high-fiber diet” had surprisingly little direct evidence for treating constipation. Specific foods performed better. That does not mean fiber is unimportant for overall health. Read our article on fibermaxxing and the science of fiber for the bigger picture.
Why Does Kiwi Work?
- Water-holding fiber. Kiwi fiber swells and holds water, which softens stool and adds bulk.
- Actinidin. This natural enzyme, unique to kiwifruit, helps break down proteins and may speed digestion in the stomach and small intestine.
- Gentle effects on gut movement. Kiwi appears to stimulate the bowel without the cramping some stimulant laxatives cause.
- Prebiotic effects. Kiwi components may support beneficial gut bacteria.
Beyond Digestion
Kiwi research has also explored other benefits, although the evidence is less established:
- Sleep: A small Taiwanese study found eating two kiwis an hour before bed improved sleep onset and quality in adults with sleep problems.
- Immune support: Kiwi is an excellent natural source of vitamin C, which supports immune function.
- Heart health: Small Norwegian studies suggested kiwis may modestly lower blood pressure and reduce platelet stickiness.
How to Enjoy Kiwi
- Cut in half and scoop with a spoon for an easy snack.
- Eat the skin of golden kiwis, or well-washed green kiwis, for extra fiber.
- Add slices to yogurt, oatmeal, or salads.
- Blend into smoothies. Note that actinidin can make dairy-based smoothies taste bitter if they sit too long.
- Use it as a natural meat tenderizer thanks to its enzymes.
Who should be careful
Kiwi is one of the more common fruit allergies. It can cause mouth itching or, rarely, serious reactions, and is more common in people with latex allergy. Stop eating kiwi and seek help if you notice swelling, hives, or trouble breathing. If you have ongoing constipation, especially with blood in your stool, weight loss, or a sudden change in bowel habits, see a doctor.
For more gentle approaches, see our guide to natural remedies for constipation and our evidence check on castor oil packs.
The Bottom Line
The kiwi does not have the exotic marketing of many superfoods, but it has something better: solid clinical evidence. Two green kiwis a day improved bowel regularity more than a common fiber supplement in a multinational trial, and the fruit is now part of the first evidence-based dietary guidelines for constipation. Cheap, delicious, and packed with vitamin C, it may be the most underrated superfood in the produce aisle.
Frequently Asked Questions
Green or gold kiwi?
The constipation trial used green kiwis. Gold kiwis are sweeter and have even more vitamin C, but green kiwis have more of the enzyme actinidin.
How long does it take to work?
Improvements were measured over four weeks, though some people notice changes within days.
Can I eat kiwi skin?
Yes. The skin is edible and adds fiber. Wash it well. Some people prefer gold kiwis, whose skin is smoother.
Is kiwi safe during pregnancy?
Yes, for those without kiwi allergy. Constipation is common in pregnancy, and kiwi is a gentle food-based option, but check with your provider.
Sources
- Gearry R, Fukudo S, Barbara G, et al. Consumption of 2 Green Kiwifruits Daily Improves Constipation and Abdominal Comfort: Results of an International Multicenter Randomized Controlled Trial. American Journal of Gastroenterology, 2023;118:1058-1068.
- King’s College London. Kiwis could help manage chronic constipation. October 2025.
- Lin HH, Tsai PS, Fang SC, Liu JF. Effect of kiwifruit consumption on sleep quality in adults with sleep problems. Asia Pacific Journal of Clinical Nutrition, 2011.
- U.S. Department of Agriculture. FoodData Central.
This article is for educational purposes and is not medical advice. See your doctor about persistent constipation or any new digestive symptoms.
