Watermelon — A Summertime Staple
Summertime picnics and holiday celebrations would hardly be complete without watermelon. But this brightly colored perennial favorite fruit offers up more than a juicy, thirst-quenching snack in hot weather.
It is well known that women’s risk for cardiovascular events increases after menopause. Compounds in watermelon may help to improve arterial stiffness and hypertension in this susceptible population. Consumption of a watermelon extract rich in L-citrulline and L-arginine (6g/day for 6 weeks) resulted in small but significant decreases in aortic and radial systolic blood pressure compared to placebo in post-menopausal women. Studies in obese adults with hypertension and pre-hypertension lend more evidence for a role for watermelon in lowering blood pressure. A small, placebo-controlled crossover study involving 14 adults (age 58 ± 1 year) showed that, compared to placebo, supplementation with watermelon extract led to significant decreases in ankle and brachial systolic & diastolic pressure, as well as mean arterial pressure.
The effects of watermelon on cardiovascular health might also be due to the fruit’s relatively high citrulline content. (In fact, citrulline was first isolated from watermelon, and the compound takes its name from the plant’s botanical name, Citrullus lanatus.) Citrulline is a metabolic precursor to arginine, with arginine influencing synthesis of the vasodilator, nitric oxide. Subjects who consumed either 780g or 1560g of watermelon juice per day for three weeks had increases in plasma arginine concentrations of 12% and 22%, respectively. Citrulline might be even more effective for supporting cardiovascular health than arginine, itself. As researchers explain, “intestinal and hepatic metabolism of L-arginine to ornithine and urea by arginase makes oral delivery very ineffective…In contrast, L-citrulline is not metabolized in the intestine or liver and does not induce tissue arginase, but rather inhibits its activity. L-citrulline entering the kidney, vascular endothelium and other tissues can be readily converted to L-arginine, thus raising plasma and tissue levels of L-arginine and enhancing NO production.”
The benefits of watermelon compounds on hemodynamics and the cardiovascular system make watermelon a nice addition to post-workout recovery for athletes. Fresh and pasteurized watermelon juice both had helpful effects on muscle soreness in healthy young men 24 hours after a maximum effort cycle ergometer test.
Watermelon is a good source of the antioxidant lycopene, also found in other red/pink fruits and vegetables, such as tomatoes and guava. In a crossover study with healthy adults, supplementation with watermelon juice resulted in significant increases to plasma lycopene, compared to no supplementation. There was no dose-response effect when the dose of watermelon juice was doubled, which suggests that there likely reaches a point when the body’s lycopene stores are replete and cannot be elevated further. It’s a nice coincidence that watermelon—a summertime staple—is so rich in lycopene, since lycopene may be protective against UV-induced photo-damage to the skin. In other words, to a certain degree, watermelon might be nature’s sunscreen!
A cup of watermelon (152g) provides 21% of the daily value (DV) for vitamin C, and 17% of the DV for vitamin A (as beta-carotene). The natural sweetness of watermelon might make those concerned about their sugar intake refrain from this delicious summer treat. However, a one-cup serving of watermelon has just 11g of carbohydrate. Compare that to a large bagel, weighing 131g (less than the watermelon), which delivers a whopping 70g of carbohydrate. Moreover, while the glycemic index of watermelon is relatively high, the glycemic load is quite low. After all, it’s not called watermelon for nothing: of the 152g by weight, 139g are water!
The peppery bite of bitter greens, such as arugula, and the saltiness of cubed feta cheese, make a classic salad to complement the sweetness of watermelon. And the bright pink flesh of a watermelon isn’t the only edible part. Nose-to-tail cooking doesn’t apply just to animal foods; you can use all parts of a watermelon in culinary applications. Pickled watermelon rind is a good way to make use of something that is typically discarded. In fact, the rind contains more citrulline than the pink flesh, and more of the phenolic compound, chlorogenic acid.
And don’t forget about the seeds! Watermelon seeds are good for more than spitting out onto the grass at family picnics. Although we don’t typically think of eating them, they’re a good source of natural fats, and they’re high in magnesium, phosphorus, zinc, and manganese. Plus, watermelon seeds contain triterpene compounds that may have mild cytotoxic properties against human leukemia cells.