What's New and Beneficial About Watermelon
Alongside of tomatoes, watermelon has moved up to the front of the line in recent research studies on high-lycopene foods. Lycopene is a carotenoid phytonutrient that's especially important for our cardiovascular health, and an increasing number of scientists now believe that lycopene is important for bone health as well. Among whole, fresh fruits that are commonly eaten in the U.S., watermelon now accounts for more U.S. intake of lycopene (by weight of fruit eaten) than any other fruit. Pink grapefruit and guava are two other important fruit sources of lycopene, although in the U.S., these fruits are more often consumed in the form of juice.
Health scientists are becoming more and more interested in the citrulline content of watermelon. Citrulline is an amino acid that is commonly converted by our kidneys and other organ systems into arginine (another amino acid). The flesh of a watermelon contains about 250 millligrams of citrulline per cup. When our body absorbs this citrulline, one of the steps it can take is conversion of citrulline into arginine. Particularly if a person's body is not making enough arginine, higher levels of arginine can help improve blood flow and other aspects of our cardiovascular health. There's also some preliminary evidence from animal studies that greater conversion of citrulline into arginine may help prevent excess accumulation of fat in fat cells due to blocked activity of an enzyme called tissue-nonspecific alkaline phosphatase, or TNAP.
If you've gotten used to thinking about the juicy red flesh at the center of a watermelon as its only nutrient-rich area—and far more nutrient-rich than the more lightly-colored flesh that is farther out near the watermelon rind—it is time to change your thinking. In a recent study, food scientists compared the nutrient content of flesh from different parts of a watermelon: flesh from the center, the stem end, the blossom end (opposite from the stem), and the periphery (the part nearest to the rind). What they've discovered were impressive concentrations of phenolic antioxidants, flavonoids, lycopene, and vitamin C in all of these different areas. The exact distribution of nutrients was also highly dependent on the variety of watermelon. But there was no area in any of the watermelon varieties that came out badly in terms of nutrients, and in many of the watermelon varieties, the flesh's outer periphery contained impressive concentrations of most nutrients.
Recent studies have confirmed the nutritional importance of allowing a watermelon to fully ripen. For example, research has shown that the biggest jump in lycopene content occurs at the time when a watermelon's flesh turns from white-pink to pink. Yet when that flesh continues to ripen, resulting in a color change from pink to red, the lycopene content becomes even more concentrated. Prior to ripening, when the flesh of a watermelon is primarily white in color, its beta-carotene content is near zero. Even when allowed to ripen to the white-pink stage, a watermelon still contains very little of its eventual beta-carotene content. But as it moves from white-pink to pink to red, the beta-carotene content of a watermelon steadily increases. Like lycopene and beta-carotene, total phenolic antioxidants in a watermelon also increase consistently during ripening, all the way up until the appearance of fully red flesh. The bottom line: eating a fully ripe watermelon can really pay off in terms of nutrient benefits. Please see our section called "How to Select and Store" to learn about determining a watermelon's ripeness before you purchase it.
Anti-Inflammatory and Antioxidant Support
Phenolic compounds in watermelon—including flavonoids, carotenoids,
and triterpenoids—make this fruit a choice for anti-inflammatory and anti-
oxidant health benefits. If you had to pick a single nutrient from this anti-
inflammatory and antioxidant category that has put watermelon on the
map, that nutrient would be lycopene. Alongside of pink grapefruit and
guava, watermelon is an unusually concentrated source of this carotenoid.
Whereas most fruits get their reddish color from anthocyanin flavonoids,
watermelon gets it reddish-pink shades primarily from lycopene. The lycopene
content of watermelons increases along with ripening, so to get the best
lycopene benefits from watermelon, make sure that your melon is optimally
ripe. (See our section entitled, "How to Select and Store" for practical tips on
selecting a fully ripe watermelon.) The lycopene in watermelon is a well-
documented inhibitor of many inflammatory processes, including the production
of pro-inflammatory messaging molecules, the expression of enzymes like
cyclo-oxygenase and lipoxygenase that can lead to increased inflammatory response, and the activity of molecular signaling agents like nuclear factor kappa B (NFkB). Lycopene is also a well-known antioxidant, with the ability to neutralize free radical molecules.
Recent research has shown that the lycopene content of watermelon also remains very stable over time. When two-inch cubes of fresh-cut watermelon were stored in the refrigerator at 36°F (2°C) over 48 hours, researchers found virtually no deterioration in lycopene content. That deterioration did not start to become significant until about seven days of storage, when it decreased by about 6-11%. While we do not recommend waiting seven days before consuming fresh cut watermelon, we believe that the excellent stability of watermelon lycopene over a two-day period is great news for anyone wanting to enjoy fresh cut watermelon over the course of several days.
Cucurbitacin E is another unique anti-inflammatory phytonutrient (called a tripterpenoid) found in watermelon. Like the carotenoid lycopene, this anti-inflammatory nutrient has been shown to block activity of cyclo-oxygenase enzymes and neutralize reactive nitrogen-containing molecules. (Interestingly, cucurbitacin E does not appear to neutralize activity of reactive oxygen species—called ROS—but only activity of reactive nitrogen species, called RNS.)
Antioxidant carotenoids found in watermelon include significant amounts of beta-carotene. Like lycopene, the beta-carotene in watermelon also increases with ripening.
Red-pink fleshed watermelons typically contain far more lycopene and beta-carotene than yellow-white fleshed varieties. For example, one study we've seen showed red watermelon to contain over 600 micrograms of beta-carotene per 3.5 ounces of melon and over 6,500 micrograms of lycopene. By comparison, yellow-fleshed varieties were found to contain only 5-10 micrograms of beta-carotene and no measurable amount of lycopene. In red/pink-fleshed watermelons as a group, we've seen lycopene amounts that vary widely in a range of approximately 2,000–6,700 micrograms per 3.5 ounces of fresh melon. Beta-carotene in these red/pink-fleshed varieties also varies widely, in a range of approximately 5–325 micrograms. Because watermelon contains so many different phytonutrients—as well as key vitamins and minerals, as well as dietary fiber—your health is going to be improved by any watermelon variety that you choose. However, if you specifically want to maximize your lycopene and beta-carotene intake, you'll most likely want to stick with red/pink-fleshed varieties of watermelon.
It would be a mistake to ignore the important amount of vitamin C found in watermelon. In our Food Rating System, watermelon qualifies as an excellent source of vitamin C, even though the amount provided (about 12 milligrams per cup of fresh melon) is only 20% of the Daily Value (DV). However, due to its very high water content, the same amount of watermelon that provides us with 20% of the Daily Value for vitamin C only costs us about 45 calories, or about 2% of our total daily calories on a 1800-2000 calorie diet. That's excellent nutrient richness, and it makes watermelon a great choice for increasing vitamin C antioxidant protection.
Citrulline, Arginine, and Nitric Oxide-Related Benefits
One of the more unusual aspects of watermelon is its rich supply of the amino acid, citrulline.
Citrulline is an amino acid that is commonly converted by our kidneys and other organ systems (including cells that line our blood vessels) into arginine (another amino acid). The flesh of a
watermelon contains about 250 millligrams of citrulline per cup. When our body absorbs
citrulline, one of the steps it can take is conversion of citrulline into arginine.
An enzyme called nitric oxide synthase (NOS)—found in many of our body's cell types—is able
to take the amino acid arginine and use it to help produce a very small molecule of gas called
nitric oxide (NO), which is a muscle relaxant. For example, when NO tells the smooth muscles
around our blood vessels to relax, the space inside our blood vessels can expand, allowing
blood to flow more freely and creating a drop in blood pressure. The relaxing of muscle tension
and increasing of blood flow is also the way that NO can change erectile function in men. (The
prescription medication sildenafil or Viagra (TM) works in this way.)
The amount of citrulline found in fresh watermelon is not enough to make it a food that can automatically improve blood pressure or affect other problems like erectile dysfunction. But in animal studies, intake of watermelon has been shown to help support cardiovascular function, including improvement of blood flow (through relaxation of blood vessels, or what is technically called vasodilation). In humans, intake of watermelon has been shown to increase blood levels of arginine, but only when consumed in very large amounts. For example, in one study that we reviewed, participants consumed either three cups or six cups of fresh watermelon juice daily over the course of three weeks and experienced increases in their blood arginine levels of approximately 12-22%.
Another fascinating new area of research involving watermelon and its citrulline content relates to the deposition of body fat. In animal studies, high intake of amino acid citrulline—followed by conversion of citrulline into the amino acid arginine—can result in the formation of arginine-related molecules called polyarginine peptides. These polyarginine peptides are able to block activity of an enzyme called tissue-nonspecific alkaline phosphatase, or TNAP. When TNAP activity is shut down, our fat cells (adipocytes) tend to create less fat (adipogenesis). Researchers believe that the connection between citrulline in food, arginine production by nitric oxide synthase, and fat cell metabolism may eventually provide us with additional tools for helping prevent over-accumulation of body fat.
At present, however, the best we can conclude about watermelon and its unusual citrulline content is that it's likely to provide us with some cardiovascular benefits, especially if we don't consume many foods that are high in arginine. (Some of the WHFoods highest in arginine include shrimp, spinach, sea vegetables, turkey, sunflower seeds, and sesame seeds.)
Other Health Benefits
Watermelon seeds can provide us with small but helpful amounts of both iron and zinc. We're talking about several hundred seeds (the amount contained in a typical seeded watermelon, which is not an amount that we would anticipate or suggest eating at one time) to obtain 1–2 milligrams of either mineral. Still, regular consumption of whole, seeded watermelon would provide us with nutrient benefits in this area over time. Interestingly, we've seen one study showing that the iron and zinc in watermelon seeds is surprisingly bioavailable (85-90%), despite the oxalates and phytates that are contained in the seeds. (Oxalates and phytates can sometimes bind with minerals like iron and zinc to lessen their bioavailability.)
The amount of protein in watermelon seeds is approximately 1 gram per 24 seeds. At this rate, we're likely to get several grams of protein when we eat several slices of whole, seeded watermelon. While we would not want to depend on watermelon as a key protein food, this valuable amount of protein in its seeds should at least remind us that a fruit like watermelon does have something to offer us in the way of protein benefits.
At approximately two-thirds of one gram of dietary fiber per cup, watermelon does not rank as a good, very good, or excellent source of this nutrient in our ranking system. However, you'd be receiving about 3-4 grams of dietary fiber if you enjoyed 175–200 calories of fresh watermelon in the form of several large slices, and this dietary fiber would include a nice mix of soluble to insoluble fiber. (Insoluble fibers can provide special support to the digestive system, and soluble fibers can provide special support to the cardiovascular system.) So while watermelon is not a concentrated source of fiber, we often enjoy it in larger amounts that can provide us with great fiber benefits at a low calorie cost.
If you have ever tasted a watermelon, it is probably no surprise to you why this juicy, refreshing fruit has this name. Watermelon has an extremely high water content, approximately 92%, giving its flesh a juicy and thirst-quenching texture while still also subtly crunchy. As a member of the Cucurbitaceae family, the watermelon is related to the cantaloupe, squash, pumpkin, cucumber, and gourd that grow on vines on the ground. Watermelons can be round, oblong, or spherical in shape and feature thick green rinds that are often spotted or striped. (Many people report, however, that they like the taste and predictable ripeness of a watermelon best if the watermelon is symmetrical in shape.) Watermelons range in size from a few pounds to upward of ninety pounds. Between 600–1,200 different varieties of watermelon exist worldwide, but all of these varieties belong to the same scientific genus and species of plant, called Citrullis lanatus.
While we often associate a deep red/pink color with watermelons, there are many varieties that feature orange, yellow, or white flesh. These varieties are typically lower in the carotenoid lycopene than red/pink varieties.
A good bit of controversy has arisen over the exact nature of seedless watermelons. Contrary to some information that you will find on various websites, seedless watermelons are not the result of genetic engineering. Seedless watermelons are the result of hybridization. By crossing a diploid watermelon (with two sets of chromosomes) and a tetraploid watermelon (with four sets of chromosomes), it is possible to produce a watermelon that contains triploid seeds (with three chromosomal sets). When planted, these triploid seeds will grow into seedless watermelons. Seedless watermelons will typically appear to contain some white seeds even though they are labeled as seedless. These white seeds are not actually seeds, but only empty seed coats.
Ten years ago, it was somewhat rare to find seedless watermelons in the marketplace. Today, up to 85% of all watermelons produced in the U.S. are estimated to be seedless. This great increase in the availability of seedless watermelons is due to the vastly increased use of "non-bearing pollinators" by watermelon growers. Previously, growers were required to interplant rows of acreage with seeded, fruit-bearing watermelons in order to pollinate their seedless varieties. Today, they are able to pollinate with plants that produce flowers needed by bees, but yield no fruit. These non-fruit-bearing plants allow pollination to continue, but in a less time-consuming and space-consuming way. It's possible to grow seedless watermelons most anywhere that seeded watermelons will grow. Some of the more common seedless varieties include Fandango, Super Cool, Honeyheart, King of Hearts, Queen of Hearts, Crimson Trio, Scarlet Trio, and SuperSweet.
Some common varieties of seeded watermelon include Jubilee, Royal Jubilee, Royal Sweet, Crimson Sweet, Sangria, Fiesta, Sugar Baby, Baby Doll, and Charleston Gray. A 15–20 pound diploid, seeded watermelon will typical contain hundreds of seeds.
Watermelons are generally believed to have originated in Africa several thousand years ago and to have traveled over time from Africa to Asia to Europe to North America. Their arrival in Asia and the Middle East is believed to date back to approximately 900–1,000 A.D., and their arrival in Europe is estimated to have occurred in 1300–1400 A.D. It was not until Europeans began to colonize North America that watermelons arrived in what is now the U.S.
Today, over four billion pounds of watermelon are produced each year in the U.S. About 85% of watermelons are purchased in fresh form by consumers. Although there is some watermelon production in virtually all states, about three-fourths of all U.S. watermelons are grown in Florida, California, Texas, Georgia, and Indiana. On an average, per person basis, we eat over 15 pounds of fresh watermelon each year.
On a global basis, China is by far the largest watermelon-producing country and accounts for over half of all world production. The European Union countries, Iran, Turkey, Egypt, Brazil, and the United States are the next largest watermelon producers, but each produces less than 5% of the world total.
How to Select and Store
If you are purchasing a pre-cut watermelon that has already
been sliced into halves or quarters, choose the flesh that is
deepest in color and lacks any white streaking. If the
watermelon is seeded, the seeds should also be deep in color,
When purchasing a whole, uncut watermelon, there are several
features to you'll want to evaluate. The first is its weight. A fully
ripened watermelon will feel heavy for its size. Heaviness in a
watermelon is a good thing because the water content of a
watermelon will typically increase along with ripening, and a fully
ripened watermelon will be over 90% water in terms of weight,
and water is one of the heaviest components in any food.
Second, look for a watermelon with a relatively smooth rind that is slightly dulled on top. The top and the bottom of a watermelon are worth determining and examining on a watermelon. The bottom or "underbelly" of a watermelon is the spot where it was resting on the ground. If that "ground spot" is white or green, the watermelon is unlikely to be fully ripe. A fully ripened watermelon will often have a ground spot that has turned creamy yellow in color. Opposite from the ground spot will be the top of the watermelon. In a fully ripened watermelon, that spot will typically not be shiny but somewhat dulled. The green color may appear in many different shades, however, from light green to deeper shades.
Perhaps most controversial about ripeness testing of a watermelon is whether or not to give it a thump. We've read many arguments both pro and con. However, among experts who recommend thumping, most seem to agree that a fully ripened watermelon will have a deeper, hollower "bass" sound rather than a solid and shallow "soprano" sound.
Finally, some grocers will be willing to core an uncut watermelon so that you can have an actual taste. (If you decide not to purchase the melon, the grocer can slice it up and sell it in sliced form.) So consider requesting this if you are uncertain as to the quality.
Uncut watermelons are best stored at temperatures of 50-60°F (10–16°C). In many regions, room temperatures will typically be warmer than 60°F and may be less than ideal for whole watermelon storage due to increased risk of decay. Better storage temperatures will typically be found in cellars or basements that are partly or completely below ground level. While we've seen one study showing increases in lycopene content when whole watermelon was stored at a temperature of 68°F (20°C), we believe that a fully-ripe or close-to-fully-ripe melon will already have outstanding lycopene content and that it would be better for you to err on the safe side in terms of decay risk if you are planning to wait several days before slicing open your watermelon.
Like temperatures above 60°F (16°C), temperatures much below 50°F (10°C) are not recommended for storage of uncut watermelons. This is due to increased risk of chilling-type injury that can decrease shelf life and flavor. (Therefore, the refrigerator would not be a good place for you to store a whole, uncut watermelon for this reason.)
With uncut, whole watermelon, one final storage precaution would be the avoidance of contact with high ethylene-producing foods like passion fruit, apples, peaches, pears, and papaya. Watermelons are ethylene-sensitive fruits that may become overly ripe too quickly under these circumstances.
Once cut, watermelons should be refrigerated in order to best preserve their freshness, taste, and juiciness. Store your cut watermelon in a sealed, hard plastic or glass container with a lid.
Tips for Preparing Watermelon
Wash the watermelon before cutting it. Due to its large size, you will probably not be able to run it under water in the sink. Instead, wash it with a wet cloth or paper towel.
Depending upon the size that you desire, there are many ways to cut a watermelon. The flesh can be sliced, cubed, or scooped into balls. Watermelon is delicious to eat as is, while it also makes a delightful addition to a fruit salad.
While many people are just accustomed to eating the juicy flesh of the watermelon, both the seeds and the rind are also edible and nutrient-rich. (In fact, in many parts of the world, watermelon seeds are widely enjoyed as a snack and pickled watermelon rind has a rich culinary tradition.) If you choose to eat the rind, we recommend purchase of certified organic watermelon. (The reason for this suggestion is an increased risk of unwanted contaminants like pesticide residues on the outer skin of non-organic watermelon.)
How to Enjoy
A Few Quick Serving Ideas
Purée watermelon, cantaloupe and kiwi together. Swirl in a little plain yogurt and serve as refreshing cold soup.
In Asian countries, roasted watermelon seeds are either seasoned and eaten as a snack food or ground up into cereal and used to make bread.
A featured item of Southern American cooking, the rind of watermelon can be marinated, pickled, or candied.
Watermelon mixed with thinly sliced red onion, salt and black pepper makes a great summer salad.
Watermelon is a wonderful addition to fruit salad. And fruit salad can be made days ahead since cut fruit, if chilled, retains its nutrients for at least 6 days.
Watermelon is not a commonly allergenic food, is not known to contain measurable amounts of oxalates or purines and is also not included in the Environmental Working Group's 2012 report "Shopper's Guide to Pesticides" as one of the 12 foods most frequently containing pesticide residues.
During the past decade, non-organic watermelons grown in part of China became the topic of widespread controversy in the popular press following the use of a synthetic growth stimulator called forchlorfenuron in their cultivation. A combination of heavy rainfall and potential overuse of the growth stimulator actually caused many watermelons on farms in Jiangsu Province to burst open, drawing media attention to this practice. While we are not aware of any data on widespread use of synthetic growth stimulators in the production of non-organic watermelon, we have seen one study predicting residues of forchlorfenuron in the range of 1-5 ppb in watermelons raised with the use of this synthetic growth stimulator. If you are seeking to lower your risk of contamination with all synthetic additives in watermelon and other foods, we recommend purchase of certified organic watermelon, since synthetic growth stimulators and other synthetic additives are prohibited in organic food production.
Watermelon is an unusual fruit source of the carotenoid lycopene and a rich
source of phenolic antioxidants. Watermelon contains cucurbitacin E, a
triterpene anti-inflammatory phytonutrient, and unusual amounts of the
amino acid citrulline. Watermelon is an excellent source of immune-
supportive vitamin C. It is also a very good source of free-radical-scavenging
vitamin A (in several carotenoid forms, and especially in the specific form of
beta-carotene). In addition, watermelon is a good source of heart-healthy
potassium and magnesium.
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Collins JK, Wu G, Perkins-Veazie P et al. Watermelon consumption increases plasma arginine concentrations in adults. Nutrition, Volume 23, Issue 3, March 2007, Pages 261-266.
Dimitrovski D, Bicanic D, Luterotti S et al. The concentration of trans-lycopene in postharvest watermelon: An evaluation of analytical data obtained by direct methods. Postharvest Biology and Technology, Volume 58, Issue 1, October 2010, Pages 21-28.
Edwards AJ, Vinyard BT, Wiley ER et al. Consumption of watermelon juice increases plasma concentrations of lycopene and beta-carotene in humans. J Nutr 2003 Apr;133(4):1043-50. 2003.
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Poduri A, Rateri DL, Saha SK et al. Citrullus lanatus 'sentinel' (watermelon) extract reduces atherosclerosis in LDL receptor-deficient mice. J Nutr Biochem. 2012 Aug 16. [Epub ahead of print].
Tlili I, Hdider C, Lenucci MS et al. Bioactive compounds and antioxidant activities of different watermelon (Citrullus lanatus (Thunb.) Mansfeld) cultivars as affected by fruit sampling area. Journal of Food Composition and Analysis, Volume 24, Issue 3, May 2011, Pages 307-314.
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Source: George Mateljan - Whole Foods Newsletter: whfoods.org
. . . . the nutritional benefits of WATERMELLON
No other fruit says summer like the subtly crunchy, thirst quenching watermelon. This is the time to enjoy it while it is in the peak of its season, is the most readily available, and the least expensive. Like tomatoes, watermelon is a good source of lycopene, a powerful antioxidant that helps protect cells and other structures in the body from oxygen damage.
Did you know that . . . .
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Herbs are Nature's Medicine?
I know, your mouth is watering . . . go get some watermelon!