Kiwifruit confers rapid mood-lifting effect

Eating kiwifruit appears to improve mood in as little as 4 days.

In a three-arm, placebo-controlled study wherein longitudinal smartphone surveys were used, supplementation with two kiwifruit daily for 4 weeks led to improved mood and vitality within 4 days, with the effects peaking around days 14 to 16. Benefits were also seen for flourishing starting at day 14. [Br J Clin Nutr 2023;doi:10.1017/S0007114523002787]

On the other hand, vitamin C supplementation at 250 mg tablet per day was associated with marginal improvements in mood that lasted approximately 12 days.

Incremental area under the curve data showed that kiwifruit had significant overall effects on mood and vitality compared with placebo, and the effects were stronger than that observed with vitamin C but were attenuated when adjusting for covariates.

In light of the findings, lead researcher Dr Benjamin Fletcher of University of Auckland, Auckland, New Zealand, highlighted the importance of getting a clear picture of the day-to-day fluctuations in mood response to vitamin C-rich foods and supplements.

“This helps us see that what we eat can have a relatively fast impact on how we feel,” Fletcher said.

Nutrient-dense fruit

Beyond its high vitamin C content, kiwifruit is a good source of fibre, folate (vitamin B9), and potassium that have been shown to contribute to mental wellbeing. The combination of these nutrients may act in synergy, working together to have a stronger effect on mood than any single nutrient would on its own, according to Fletcher and colleagues. [J Agric Food Chem 2004;52:5472-5475; Eur J Nutr 2018;57:2659-2676]

For example, fibre in kiwifruit promotes a healthy gut microbiome, which research links to improved mood, while potassium regulates stress hormones and reduces negative mood states. Together, fibre and folate have been associated with lower depressive symptoms. [Curr Opin Psychiatry 2015;28:1-6; Psychother Psychosom 2003;72:80-87; Br J Nutr 2008;100:1038-1045]

This same principle of synergy may extend beyond single fruits to one’s entire diet. As such, Fletcher encouraged a holistic dietary approach to nutrition and wellbeing by incorporating a variety of foods rich in essential nutrients.

Vitamin C

In the study, 155 adults (age 18–35 years, 63 percent women) with low plasma vitamin C (<40 μmol/l) were randomly assigned to groups receiving kiwifruit (two per day, n=54), vitamin C tablets (one 250-mg tablet per day, n=51), or placebo (one tablet per day, n=50) for 8 weeks. All participants completed smartphone surveys to report their vitality, mood, flourishing, sleep quality, sleep quantity, and physical activity.

Plasma vitamin C levels increased rapidly and peaked after 2 weeks of supplementation in the kiwifruit and vitamin C arms.

In sensitivity analyses, improvements in total mood disturbance were most pronounced for participants with low vitamin C levels at baseline when supplemented with either kiwifruit or vitamin C tablets. This, according to researchers, are in line with previous findings suggesting that individuals with consistently low vitamin C at baseline are more likely to benefit from nutritional intervention. [J Nutr Sci 2013;2:e24; Nutrients 2020;12:2898]

Fletcher and colleagues acknowledged vitamin C as a possible mechanism contributing to mood improvements from fruit and vegetable consumption that should be explored in future studies.

“Our participants had relatively good mental health to begin with [and] so had little room for improvement, but still reported the benefits of kiwifruit or vitamin C interventions,” Fletcher noted.

Taken together, the findings provide a practical, readily available approach to supporting one’s mental wellbeing, added study co-researcher Professor Tamlin Conner of University of Otago, Dunedin, New Zealand. “It's great for people to know that small changes in their diet, like adding kiwifruit, could make a difference in how they feel every day.”

In addition, “the use of intensive smartphone surveys offers a real-time understanding of the day-to-day changes in mood-related outcomes,” Conner said.