Chronic constipation is a common presenting concern in primary care and gastroenterology clinics. Multiple factors can contribute to constipation, including dietary habits, physical activity, dehydration, medication side effects, systemic diseases, and pelvic floor dysfunction. While many new medications have been developed, patients are often interested in conservative and natural remedies to medical illnesses. Rich in fiber and protease enzymes, in addition to a plethora of micronutrients, kiwifruits hold a unique ability to retain water and bulk feces. By virtue of unique proteolytic enzymes, they can further aid in digestion and promote food transit. Recent studies underscore the efficacy of consuming two kiwifruits daily in addressing functional constipation and constipation-predominant irritable bowel syndrome symptoms through alleviating constipation as well as abdominal pain, bloating, and dyspepsia. This article will review the evidence in support of kiwifruit use for constipation management as well as provide suggestions for sustainable incorporation into the diet.

Introduction

Chronic constipation is a common gastrointestinal disorder, affecting 8-12% of adults in the U.S.; its prevalence increases with age and is twice as common among women.¹ In clinical practice, constipation is most simplistically and pragmatically defined as unsatisfactory defecation in the setting of reduced stool frequency, hardened stool consistency, and/or difficulty with stool evacuation. Patients can further report straining, prolonged time spent on the toilet, a sensation of incomplete emptying, or the requirement of manual maneuvers to remove stool. It is often associated with other gastrointestinal symptoms, including abdominal discomfort, pain, bloating, and distention. When such symptoms persist for more than a month, constipation is considered chronic. Kiwifruit offers patients a natural alternative in the management of constipation, abdominal pain, and dyspepsia with randomized controlled trials supporting its efficacy. 

Why does chronic constipation happen?

The pathophysiology of constipation is multifactorial, and it is paramount to evaluate for identifiable causes and risk factors. While some risk factors are unmodifiable, such as older age and female sex, many risk factors can be reversed, including low dietary fiber intake, dehydration, physical inactivity, and medication adverse effects.

A common etiology of constipation that is often associated with a delay in diagnosis is the spectrum of evacuation disorders. These include structural disorders that create a mechanical obstruction, such as enteroceles, rectoceles or rectal intussusception, and those associated with the dissipation of the defecatory force, such as in descending perineum syndrome and rectal prolapse. Functional evacuation disorders, namely dyssynergic defecation, may manifest as paradoxical involuntary contraction or non-relaxation of the anal sphincter and puborectalis muscle during defection and/or inadequate abdomino-rectal propulsive force generation. Given the prevalence of dyssynergic defecation, estimated in some studies to affect nearly 20% of patients with chronic constipation, it is recommended to perform anorectal manometry early in the course of evaluation, especially if the patient exhibits symptoms suggestive of an evacuation disorder.² This is further supported by the efficacy of biofeedback therapy, which can be upwards of 70%.³ Aside from defecatory dysfunction, chronic constipation subtypes include functional constipation and constipation-predominant irritable bowel syndrome, as well as slow transit constipation and normal transit constipation. 

Constipation can also be secondary to medications and systemic diseases, as shown in Table 1. It is worth noting that constipation can precede the identification of the underlying disorders’ primordial symptoms, particularly in scleroderma, Parkinson’s, and neuropathy.

How is chronic constipation managed?

In managing constipation, the initial approach often hinges on dietary modifications, promotion of physical activity, and over-the-counter fiber supplementation.⁴ Although general guidance emphasizes increasing fiber through dietary staples like whole grains, fruits, and vegetables, few natural foods have been tested in clinical trials to validate their individual benefits for constipation management. Nevertheless, the spotlight is gradually shifting towards functional foods. These are foods that are recognized to provide health advantages beyond basic nutrition, with examples including aloe, rhubarb, figs, prunes, and kiwifruit.⁵ 

The typical management of constipation typically follows the order of:

Lifestyle modifications, including dietary changes, increased physical activity, and hydration

Laxatives: 

Bulk-forming laxatives (such as psyllium and methylcellulose, the latter being a non-fermentable, synthetic fiber)

Osmotic laxatives (such as polyethylene glycol and milk of magnesia)

Stimulant laxatives (such as bisacodyl and senna, whose long-term use is avoided)

Prescription medications:

Chloride channel activators (lubiprostone)

Guanylate cyclase-C agonists (linaclotide and plecanatide)

Sodium/hydrogen exchange inhibitors (tenapanor)

5-HT4 serotonin receptor agonists (prucalopride)

Ingested vibrating capsules. 

Peripherally acting mu-opioid receptor antagonists (or PAMORAs; methylnaltrexone and naloxegol) for patients with opioid-induced constipation

While lifestyle modifications are often taken for granted, certain dietary modifications, like the addition of kiwifruit, are often underutilized and can be introduced into the management of constipation at any point in the course of treatment.

How does kiwifruit help constipation?

Kiwifruit is available in two main varieties: green and gold. The green kiwifruit (Actinidia deliciosa, cultivar Hayward) and the gold kiwifruit (Actinidia chinensis, cultivar Zesy002) are the two most widely consumed varieties. Over the past few years, they have gained traction as a dietary intervention for various gastrointestinal concerns, particularly constipation. This food’s nutritional profile has many potential mechanisms explaining its laxative benefits, in addition to being generally regarded as a nutrient-dense, low-calorie fruit considering its high fiber, water, and micronutrient content, as highlighted in Table 2. 

Fiber and water content – One green kiwifruit of around 80g contains 2.4g of fiber while a similar gold kiwifruit contains 1.1g of fiber.⁶ As a reference, the USDA 2020-2025 dietary guidelines for Americans recommends 14g of fiber per 1000 calories. Americans should thus, on average, consume between 25-30g of fiber per day. Two green kiwifruits per day provide around 20% of the daily recommended intake of fiber. The fiber content of kiwifruit is approximately one-third soluble fiber, mainly composed of pectic polysaccharides which are fermentable fibers; and two-thirds insoluble fiber mainly composed of cellulose and hemicellulose which are non-fermentable and fermentable fibers. The insoluble fiber content is thought to stimulate water secretion and thereby improve stool transit time, while the soluble fiber binds to water, creating a gel that helps to soften and bulk the stool.⁷ Kiwifruit’s fiber content is particularly unique in its capacity to swell, passively increasing its volume in water, and in its elevated water retention capacity, distinguishing it from other high-fiber fruits like apple and even psyllium husk.⁸ 

Simple Carbohydrate content – Green kiwifruit contains approximately 7g of sugars, split evenly between glucose and fructose, while the sweeter-tasting gold kiwifruit contains 10g of sugars with a similar distribution of glucose and fructose.⁹ Given the absence of polyols and oligosaccharides, kiwifruit is an appropriate addition to a low fermentable oligo-, di-, mono-saccharides and polyols (FODMAP) diet. This stands in contrast to other fruits recommended for constipation such as prunes, which are high in sorbitol and may lead to bloating, diarrhea, and discomfort in patients unable to digest sorbitol. A small study showed that ingestion of 2 kiwifruit was not associated with increases in hydrogen or methane levels on breath testing, consistent with this notion.¹⁰ 

Protein and amino acids -While kiwifruit is not a high-protein food, with under 1g protein per fruit, the proteins and amino acids contained within it are significant.⁹ Actinidin, the primary protein in kiwifruit, is a protease enzyme that can aid digestion. Remarkably, actinidin remains stable against pepsin degradation and displays broad proteolytic action, especially in the acidic environment of gastric pH.¹¹ It has been shown to quickly digest ingested proteins, with evidence of improving gastric emptying time.^12,13 While the protein concentrations of most kiwifruit cultivars are comparable, there is a marked variation in their enzymatic activity.¹³ Specifically, the green kiwifruit actinidin’s proteolytic activity is much greater (about eight times greater) than that of the SunGold™ kiwifruit.^11,13 Gold kiwifruit varieties other than the SunGold™ variety have little to no actinidin.¹³ Beyond actinidin, kiwifruit houses other proteins and derivatives like kiwellin, kissper, and thaumatin-like protein, which have also been shown to exhibit anti-inflammatory, anti-bacterial, and anti-fungal activities.¹⁴ Interestingly, the kiwifruit’s kissper protein exhibits ion channel-like, pore-forming properties, suggesting that modulation of the intestinal membrane permeability may be one of the mechanisms for alleviating constipation.¹⁵ 

Micronutrients – While they may not contribute to its laxative effect, the kiwifruit is an excellent source of vitamins, particularly vitamin C, vitamin E, and folate. It is also rich in other antioxidants, such as phenolics and carotenoids, including lutein, violaxanthin, and β-carotene.⁶ Furthermore, it is a significant source of potassium, containing around 6 mEq of potassium per kiwifruit.⁶ 

Evidence Supporting Kiwifruit for Constipation

Historically, knowledge of kiwifruit’s gastrointestinal benefit can be traced back to the Tang Dynasty (circa 600 AD).⁶ A pioneering human study in 2001 offered evidence on this matter, revealing that kiwifruit improved bowel movement frequency, consistency, volume, and ease of defecation among healthy elderly participants.¹⁶ Subsequent studies have echoed these positive findings, particularly among patients with functional constipation (FC) and constipation-predominant irritable bowel syndrome (IBS-C), the latter being characterized by abdominal pain. In these studies, participants typically consumed 2-3 kiwifruits daily from either the green or gold variety, though some trials explored the impact of powdered kiwifruit extract.

In a recent 2023 international multicenter, randomized crossover study of patients with FC and IBS-C, the consumption of two peeled green kiwifruit per day (providing 6g of fiber) as compared to 7.5g of psyllium fiber was associated with an increase in the number of complete spontaneous bowel movements (CSBM), at an increase of 1.5 CSBM per week for FC and 1.7 CSBM per week for IBS-C.¹⁷ On the other hand, psyllium was associated with a non-significant increase of 0.7 CSBM per week for FC and a significant increase of 1.3 CSBM for IBS-C. Comparing the improvement with kiwifruit to that with psyllium showed kiwifruit to be superior (overall increase in CSBM of 1.7 vs. 0.9, p=0.038).¹⁷ There was also a statistically significant improvement in stool consistency and straining for both kiwifruit and psyllium, again showing kiwifruit to be superior.¹⁷ Another similarly designed study from New Zealand was published in 2022, comparing two gold kiwifruits to 7.5g of psyllium fiber.¹⁸ Findings revealed comparable efficacy between the interventions with an increase of approximately 1 CSBM weekly for gold kiwifruit and around 1.5 weekly for the psyllium (p=0.63 in comparing interventions).¹⁸ Chey et al., found that two green kiwifruit daily were associated with a mean increase of 1 CSBM weekly.¹⁹ In contrast, 12g psyllium provided an increase of 1.7 CSBM weekly and prunes offered 2.¹⁹ Beyond the number of bowel movements, kiwifruit intake also improved stool consistency, reduced straining, and mitigated the sensation of incomplete evacuation.¹⁹ Of note, for those with constipation, an improvement of over 1 CSBM weekly constitutes a clinically meaningful amelioration. 

The Impact of Kiwifruit on Symptoms Associated with Constipation

A 2022 systematic review delved into kiwifruit’s benefits in gastrointestinal symptoms other than constipation.²⁰ They found that there was good evidence supporting a positive influence of kiwifruit, particularly green kiwifruit, on abdominal discomfort and pain (good evidence, medium-high quality), abdominal distention and bloating (medium evidence, medium quality), disrupted swallowing and reflux (good evidence, high quality), and indigestion or dyspepsia (good evidence, high quality).²⁰ The evidence supporting gold kiwifruit in this context was weaker, with low evidence for abdominal discomfort/pain and disrupted swallowing/reflux, no evidence for abdominal distention/bloating, and good evidence only for indigestion/dyspepsia. 

Evidence Regarding Kiwifruit Extracts

Despite the evidence showing the benefit of kiwifruit for constipation, studies investigating the effect of kiwifruit supplements (often freeze-dried powders) have not shown similar benefits. ²¹ It is likely that components of the fresh fruit are crucial to derive its benefits. However, the single positive randomized controlled trial that demonstrated evidence supporting kiwifruit supplements used Kivia powder containing Zyactinase^TM at a dose of 5.5g per day, compared to other studies which used 0.6g to 1g of other kiwifruit extracts.^21,22 This study found improvements in the frequency and consistency of bowel movements as well improvements in abdominal discomfort, flatulence, and urgency.²² As such, the benefit appears to be related to dosage and extract formulation, similar to how the benefit of fresh kiwifruit is related to the quantity and strain of the ingested fruit. 

How to Apply Research Results in the Clinic

In clinical settings, we recommend presenting kiwifruit as a potential treatment option, especially for patients with mild symptoms and those reluctant to take medications. Patients can be counseled to eat two to three kiwifruits per day, ideally of the green Hayward variety, as the evidence is strongest for this cultivar. The gold cultivar may be offered as well if the green variety is not palatable, but the supportive evidence is weaker. There is some evidence that consuming the kiwifruit flesh with its skin may enhance the beneficial effects on gastrointestinal symptoms, although most studies were performed on peeled kiwifruit.²³ Therefore, we suggest deferring the choice to the patient given the unappetizing texture of the skin. While there is no evidence regarding the timing of consuming the fruits, it is likely that consuming the fruit near meals may be beneficial given their potential digestive benefits.

From Clinic to Bowl –
How to Make it Sustainable

Kiwifruit is generally palatable and well-received. In a 2021 study by Chey et al., only 7% of those assigned to consume kiwifruit for constipation reported dissatisfaction, in comparison to 17% for prunes and 38% for psyllium.¹⁹ While kiwifruit can easily be enjoyed on its own, strategies to avoid taste fatigue can include the creative methods of incorporated kiwifruit into the diet as described in Table 3. It is also worth noting that while most studies specify that fruits were ingested whole, there is no evidence to suggest that blending kiwifruit is detrimental. Juicing, on the other hand, is not recommended as the juice extraction process removes most of the fruit’s fiber content. Similarly, baking kiwifruit is not ideal as the heat is likely to denature the enzymes, detracting from its benefits.²⁴ 

Conclusion

The management of chronic constipation can be challenging. Given the compelling evidence, kiwifruits should be added to the healthcare provider’s therapeutic toolkit. A daily intake of two green kiwifruits offers a promising option for constipation management through enhancing stool frequency, consistency, and ease of evacuation. Kiwifruits are further likely to benefit associated symptoms of abdominal pain, bloating, indigestion, and reflux. While their palatability is generally well-received, it can be pivotal to proactively discuss the potential for taste fatigue with patients to improve sustained treatment adherence. Two kiwifruits a day may truly keep the gastroenterologist away. 

References

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