Anti-Inflammatory and Antioxidant Support
Phenolic compounds in watermelon—including flavonoids, carotenoids, and
triterpenoids—make this fruit a choice for anti-inflammatory and
antioxidant 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 very
good source of vitamin C, even though the amount provided (about 12
milligrams per cup of fresh melon) is only 16% of the Dietary Reference
Intake (DRI). However, due to its very high water content, the same
amount of watermelon that provides us with 16% of the DRI for vitamin C
only costs us about 46 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. By : http://www.whfoods.com/
