Food as Medicine: Watermelon (Citrullus lanatus, Cucurbitaceae)

History and Traditional Use


Range and Habitat

The watermelon is the largest edible fruit grown in the United States: an annual trailing plant with fruits that can grow from 5-50 pounds and vines that can reach up to 20’ in length. Each fruit forms from a yellow flower, and the spherical or ovoid fruit is typically smooth and green or green with lighter banded stripes. The watermelon is native to the Kalahari Desert in Africa, and it thrives in well-draining, sandy soil. Currently, watermelons are cultivated all over the world, with Asia producing 60% of watermelons globally. The United States ranks fifth in global watermelon production. Forty-four states grow watermelons, including Texas, Florida, Georgia, and California, which collectively produce 2/3 of all the watermelons domestically.

Phytochemicals and Constituents

Watermelon contains an array of important vitamins and minerals including vitamin A, vitamin C, vitamin B-6, potassium, and beta-carotene. Watermelon also contains the important bioactive compounds citrulline and lycopene. Vitamin C acts as an antioxidant and anti-cancer agent. Watermelon’s vitamin C content may be linked to reducing blood pressure, as does its smaller amounts of vitamins B6 and E. The human body converts beta-carotene into vitamin A, which promotes healthy eyes, a strong immune system, and healthy skin. Vine fruits like watermelon are a good source of potassium, a crucial electrolyte for nerve and muscle function. Potassium is an essential nutrient as the body ages, as it decreases high blood pressure and reduces the risk of kidney stones, stroke, and bone density loss.

Citrulline is a precursor to the amino acid arginine and is involved in the process of removing nitrogen from the blood and eliminating it through urine. Arginine is a precursor for the synthesis of nitric oxide in the body, which is a vasodilator (blood vessel-widening agent). Conditions that benefit from vasodilation, such as cardiovascular diseases, erectile dysfunction, and headaches may benefit from increased arginine intake. Arginine also helps the body make protein, which boosts muscle growth, enhances wound healing, combats fat accumulation, and stimulates the immune system.

Though the tomato (Solanum lycopersicum) is more well-known as a source for lycopene (and in fact, its name is derived from lycopersicum), lycopene is a carotenoid found in many red foods, including watermelon, papaya (Carica papaya), pink grapefruit (Citrus x paradisi), and red carrots (Daucus carota subsp. sativus). A powerful antioxidant, lycopene may help prevent heart disease and has shown a potent ability to protect the body from “free radicals,” which may play a role in the development of heart disease, Alzheimer’s disease, and many cancers. Lycopene may also boost sperm counts and lower the risk of prostate cancer.

Historical and Commercial Uses

Though native to the African Kalahari desert, where the watermelon gourd was often used as a canteen, the cultivation of watermelon spread quickly, and other cultures adopted it as a beneficial, healing food. Ancient Egyptians used watermelon to treat reproductive problems such as erectile dysfunction and prostate inflammation. The peoples of Russia and Central Asia used watermelon as a diuretic and to cleanse the blood. In Traditional Chinese Medicine, watermelon is considered cooling and moistening, producing a diuretic effect, and commonly is used to treat thirst, edema, and inflammation of the kidney and urinary tracts.18 Because watermelon is 92% water, many traditional uses of watermelon overlap with current uses, including hydration, cleansing, and eliminating impurities. Since watermelon is digested relatively quickly, the folk traditions of the Papua New Guinea aborigines known as Onabasulu advised against eating watermelon and other juicy fruits after a heavy meal or if suffering from a stomachache.

African cuisine treats the watermelon as a vegetable and uses the entire fruit: seeds, rinds, and flesh. The seeds are eaten as snacks added to dishes or ground into flour for use in baked goods. The rind can be stir-fried, stewed, candied, pickled, or grilled. The flesh is eaten or juiced, but it can also be fermented into alcohol; in the southern part of Russia, the juice is combined with hops to make beer.

Modern Research

The traditional uses for watermelon as a medicine are beginning to gain scientific confirmation, particularly in regards to its applications against erectile dysfunction, dehydration, kidney disease, and anti-aging concerns. Watermelon’s antioxidant and nutrient content defend against many different conditions.

Current research shows that citrulline in watermelons has beneficial effects on the heart, dilating the blood vessels and improving blood flow. In one clinical study, obese participants with pre-high blood pressure or stage-one high blood pressure significantly reduced their ankle and brachial systolic blood pressure, diastolic blood pressure, mean arterial pressure, and carotid wave reflection with ingestion of citrulline from watermelons. A review of consumption of citrulline from watermelon demonstrated improvements in glycemic control and circulatory problems in diabetics, a reduction in cardiovascular risk factors, and increased levels of arginine, an essential amino acid. Because arginine is involved in maintaining the health of the reproductive, pulmonary, renal, gastrointestinal, hepatic, and immune systems, citrulline is of increasing interest in the realm of scientific study. Studies show that citrulline is more bioavailable in the body than arginine, making it a better candidate for arginine deficiency diseases such as renal carcinoma, chronic inflammatory diseases, or blood cell diseases like sickle cell anemia and malaria. Citrulline research also has shown promising results of becoming a biomarker for bowel problems of the small intestine as well as kidney failure.13

Lycopene’s powerful antioxidant properties have been shown to reduce the risks of prostate, lung, gastric, and colorectal cancers. However, due to its antioxidant effect, it seems to interfere with chemo and radiation therapy. In addition to being an antioxidant, lycopene has been shown to be heart-protective and lowers LDL cholesterol. In one study, lycopene ingestion showed a reduction in the risk of stroke, especially ischemic strokes in men. Finally, lycopene has been linked to a reduction in cardiovascular risks.

Nutrient Profile


Macronutrient Profile
(Per 1 cup diced watermelon [approx. 152 g]):

46 calories
1 g protein
11.5 g carbohydrate
0.2 g fat

Secondary Metabolites (Per 1 cup diced watermelon [approx. 152 g]):

Excellent source of:

Vitamin C: 12.3 mg (20.5% DV)
Vitamin A: 865 IU (17.3% DV)

Very good source of:

Potassium: 170 mg (4.9% DV)

Also provides:

Magnesium: 15 mg (3.8% DV)
Vitamin B-6: 0.07 mg (3.5% DV)
Thiamin: 0.05 mg (3.3% DV)
Vitamin E: 0.08 mg (3% DV)
Manganese: 0.06 mg (3% DV)
Dietary Fiber: 0.6 g (2.4% DV)
Iron: 0.4 mg (2.2% DV)
Phosphorus: 17 mg (1.7% DV)
Folate: 5 mcg (1.3% DV)
Calcium: 11 mg (1.1% DV)

DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000 calorie diet.


Recipe: Pickled Watermelon Rinds

Adapted from Bon Appétit


For an equally delicious condiment without the wait, use these ingredients to make watermelon rind chutney: increase sugar to 1 ½ cups, water to 1 cup, and finely mince the ginger. Bring all ingredients to a boil in a large pan, then simmer for 45-60 minutes until the rind is translucent and tender and the liquid reduces and thickens. Remove whole spices before serving.

Ingredients:

  • 4 lbs of watermelon
  • 1 serrano chili, thinly sliced, seeds removed if desired
  • 1-inch piece of fresh ginger, peeled and thinly sliced
  • 2-star anise pods
  • 1 tablespoon kosher salt
  • 1 teaspoon black peppercorns
  • 1 cup sugar
  • 1 cup apple cider vinegar

Directions:

  1. Using a vegetable peeler, remove the tough green outer rind from watermelon; discard.
  2. Slice watermelon into 1”-thick slices. Cut away all but 1/4” of flesh from each slice; reserve flesh for another use. Cut rind into 1” pieces for roughly 4 cups of the rind.
  3. Bring chili, ginger, star anise, salt, peppercorns, sugar, vinegar, and 1/2 cup of water to a boil in a large, non-reactive saucepan, stirring to dissolve sugar and salt.
  4. Add watermelon rind. Reduce heat and simmer until just tender, about 5 minutes. Remove from heat and let cool to room temperature, setting a small lid or plate directly on top of rind to keep submerged in brine, if needed.
  5. Transfer rind and liquid to an airtight container; cover and chill at least 12 hours.