Lycopene, L-citrulline, vitamin C and potassium: what the research says about watermelon's nutritional profile beyond its 92% water content.
Watermelon's reputation as "basically water" undersells it: at roughly 92% water by weight, it is indeed one of the most hydrating fruits available, but the remaining 8% carries a nutritional profile that has drawn real scientific attention, not just marketing claims.
More lycopene than a tomato
Watermelon contains more lycopene — the pigment responsible for its red flesh — than any other fruit or vegetable, including tomatoes. Research on lycopene has linked it to a reduced risk of heart disease and stroke, anti-inflammatory effects, and a potential role in slowing the growth of certain cancer cells, with prostate cancer specifically studied. Watermelon also supplies vitamin C, provitamin A carotenoids, magnesium, and potassium alongside the lycopene.
L-citrulline: the amino acid behind the "watermelon for athletes" claims
Watermelon is one of the richest natural sources of L-citrulline, an amino acid the body converts into nitric oxide, a molecule that helps relax blood vessels and supports healthy blood flow. A study published in the Journal of Agricultural and Food Chemistry found that athletes who drank watermelon juice experienced reduced muscle soreness for up to 24 hours after exercise, along with a lower recovery heart rate — researchers linked the effect specifically to the fruit's L-citrulline content. Researchers note that larger, longer-term studies are still needed before these findings translate into firm dietary guidance, but the existing research base is real and growing.
Why this matters for how we handle the fruit after harvest
Lycopene and citrulline concentrations both increase as a watermelon fully ripens on the vine, which is one more reason correct harvest timing — judged by the field spot, stem, and sound signs covered in our guide to choosing a ripe watermelon — matters as much for nutritional value as it does for taste. A watermelon picked too early isn't just less sweet; it also hasn't developed its full lycopene and citrulline content.
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Frequently Asked Questions
Does watermelon really contain more lycopene than tomatoes?
Yes — watermelon contains more lycopene, the pigment responsible for its red flesh, than any other fruit or vegetable, including tomatoes.
What is L-citrulline and why is it linked to watermelon?
L-citrulline is an amino acid the body converts into nitric oxide, which helps relax blood vessels; watermelon is one of its richest natural sources, and a study found watermelon juice reduced post-exercise muscle soreness in athletes.