Kiwi

Kiwifruit (Actinidia) — the common green kiwi and the gold-fleshed sungold variety — is unusually nutrient-dense for a fruit. A serving (two kiwis) provides more than a day's vitamin C, meaningful fiber, vitamin K, and several antioxidants. It also contains actinidin, an enzyme that breaks down proteins — one reason kiwi can be used to tenderize meat.

Two kiwi-specific evidence streams stand out: a small body of randomized trials suggesting modest sleep benefit when eaten before bed, and observational/small-trial data showing improved bowel function in people with constipation (likely from fiber + actinidin).

Sleep and digestion evidence

A 2011 Taiwanese trial in adults with sleep complaints found that eating two kiwis an hour before bedtime for four weeks improved sleep onset, total sleep time, and self-reported sleep quality compared to baseline. The mechanism is uncertain — kiwi contains some serotonin and folate, both potentially relevant — but the trial has been cited often despite the small sample. For constipation, several trials show two kiwis a day improves stool frequency and reduces straining, comparable to or better than prunes.

Allergy caveat

Kiwi is a meaningful (though not "top eight") food allergen. It's a common cause of oral allergy syndrome — itching or mild swelling in the mouth — particularly in people allergic to birch, grass, or latex pollens via cross-reactivity. True systemic kiwi allergy with anaphylaxis is rarer but documented. For most people kiwi is safe and useful; those with severe pollen allergy who notice oral symptoms after kiwi should see an allergist before continuing.