Watermelon

Health Benefits
(Source: World's Healthiest Foods, George Mateljan)

Anti-Inflammatory, Antioxidant, and Cardiovascular Benefits from Watermelon

It is the diversity of phytonutrients in watermelon—and some key players in this group—that make this fruit unique in terms of anti-inflammatory and antioxidant benefits. You will find many different types of phenolic phytonutrients in watermelon, including carotenoids, flavonoids, and triterpenoids. Among these phytonutrients, lycopene (a carotenoid) and cucurbitacin E (a triterpenoid) stand out from a research perspective as being most closely related to this fruit's antioxidant and anti-inflammatory benefits. In the case of lycopene, you can expect to receive an average amount of 4–5 milligrams of lycopene in every 100 grams (approximately two-thirds cup in volume) of red-fleshed watermelon. This amount makes red-fleshed watermelon–on average–more concentrated in lycopene than red tomatoes, which usually contain about 3–4 milligrams per 100 grams (approximately one-half cup in volume). Moreover, the bioavailability of lycopene from red-fleshed watermelon appears to be greater than its bioavailability from red tomato. This greater bioavailability may have to do with the presence of cis-isomeric lycopene in red-fleshed watermelon, which is a more readily available form of this carotenoid. (At WHFoods, our top lycopene sources include not only watermelon and tomato but also papaya and pink grapefruit.) Lycopene is a carotenoid that has been best studied in relationship to cardiovascular disease, where it has repeatedly been shown to lower disease risk through scavenging of lipid peroxyl radicals and reactive oxygen species (ROS). Deficiencies in lycopene over the course of aging have also been associated with increased age-related cardiovascular disease. The lycopene richness in red-fleshed watermelon makes this fruit a logical choice for increased antioxidant protection, particularly as it relates to our cardiovascular system.

We think about cucurbitacin E as a second featured phytonutrient in watermelon that acts to complement the activities of lycopene. Cucurbitacin E is a triterpenoid that is known to lessen unwanted inflammation by inhibiting the activity of the enzyme cyclooxygenase-2 (COX-2). Unlike lycopene, however, it does not appear to be especially effective in the scavenging of ROS. However, it has been shown to be very effective in the scavenging of RNS (which stands for reactive nitrogen species). By combining these two phytonutrients together (lycopene and cucurbitacin E), watermelon is able to provide us with improved scavenging of both oxygen and nitrogen radicals, and to lessen our risk of undesirable oxidative stress or chronic unwanted inflammation.

Within the context of cardiovascular benefits, it's important to recognize a third nutrient in watermelon present in unusual amounts. This nutrient is the amino acid citrulline. While the amount of citrulline in watermelon flesh can vary significantly, the cup of fresh watermelon that we profile on our website is estimated to contain between 200–300 milligrams of citrulline. One primary way in which citrulline can provide us with cardiovascular support is through its role in a metabolic process known as the urea cycle. In this cycle, three amino acids—citrulline, arginine, and ornithine—undergo interconversion. During this interconversion process, a key cell signaling molecule—nitric oxide (NO) —can get produced. NO plays a key role in regulation of blood pressure since it has the ability to increase expansion of our blood vessel diameter, thus lowering the pressure at which our blood flows. Levels of NO have also been determined to play a key role in the regulation of our blood sugar. Since NO is directly produced from the conversion of arginine into citrulline, researchers have long been interested in the degree to which citrulline intake can affect the overall balance of citrulline, arginine, ornithine, and NO in this area of metabolism.

Similarly, researchers have wondered if a citrulline-rich food like watermelon might provide us with potential cardiovascular benefits. One recent study has looked at this exact set of questions in a group of participants who consumed between 3–6 cups of watermelon juice per day over a period of several weeks. What the researchers found was a steady and well-maintained level of citrulline in the bloodstream of the participants, as well as an increased level of arginine. They concluded from these findings that citrulline from the watermelon juice had undergone conversion into arginine, while leaving plenty of citrulline to stabilize blood levels. In other words, the citrulline from watermelon was viewed as improving balance in this area of metabolism. These findings add to the research evidence for watermelon as a fruit that can lower our risk of high blood pressure and type 2 diabetes especially since arginine deficiency—whether chronic and moderate or temporary and serve deficiency—has been linked to increase risk of both health problems.

When considering antioxidant benefits from watermelon, it would be wrong to overlook vitamin C and beta-carotene. In our Food Rating System, watermelon qualifies as very good source of vitamin C, providing about 12 milligrams per fresh cup. Two cups' worth of this delicious fruit means that one-third of our daily recommended vitamin C intake has already been met. Watermelon ranks as a good source of vitamin A in our food rating system, and this rank is largely due to its beta-carotene content. (While watermelon contains a far greater amount of lycopene than beta-carotene, researchers do not take lycopene into account when estimating vitamin A activity since lycopene is a cartenoid that cannot be converted into retinol. Beta-carotene, however, is the best non-retinol form of carotenoids for conversion into vitamin A.) Beta-carotene is typically highest in red-fleshed varieties of watermelon, although amounts can vary greatly, in a range of approximately 5–325 micrograms per 100 grams. But even in the lower half of this range, we are getting valuable antioxidant benefits from the beta-carotene content of watermelon.

Other Potential Health Benefits from Watermelon

We've seen a good bit of animal research on watermelon extracts, watermelon powders, and isolated watermelon phytonutrients (like lycopene, citrulline, or cucurbitacin E) in a variety of other health areas, notably in the area of cancer risk. In this area, watermelon research has often focused on types of cancer called "aerodigestive cancers." These types of cancer include cancers of the oral cavity (mouth), larynx (voice box), pharynx (passageway connecting our nose to our mouth and throat), and esophagus (connecting our mouth to our stomach). Based on the study details that we have seen to date, we would summarize this research as being in the preliminary stages and quite far from being expanded to everyday intake of watermelon in a typical meal plan.

In the context of "other potential health benefits" from watermelon, we also want to mention the seeds of this fruit. Watermelon seeds have been the topic of growing health research and have been studied in their own right for their antioxidant and anti-inflammatory capacity. From a nutrient perspective, watermelon seeds are every bit as nutrient rich as the flesh of this fruit—and perhaps even more so. For example, you will find flavonoids, carotenoids, saponins, phenolic acids, proteins, carbohydrates, and fats in watermelon seeds. For the most part, research on watermelon seeds has focused on the same key areas of potential health benefits as research on the flesh of this fruit, namely, antioxidant, anti-inflammatory, and cardiovascular benefits.

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