Watermelon: Health Benefits, Risks & Nutrition Facts
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Watermelons are mostly water — about 92 percent — but this refreshing fruit is soaked with nutrients. Each juicy bite has significant levels of vitamins A, B6 and C, lots of lycopene, antioxidants and amino acids. There's even a modest amount of potassium. Plus, this quintessential summer snack is fat-free, very low in sodium and has only 40 calories per cup. 

"Foods that are high in antioxidants and amino acids allow your body to function optimally," said Angela Lemond, a Plano, Texas-based registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics. "Antioxidants help prevent damage, and cancer. Amino acids are the basic building block for protein, and protein is used in virtually every vital function in the body."

Scientists have taken notice of watermelon's high lycopene levels — about 15 to 20 milligrams per 2-cup serving, according to the National Watermelon Promotion Board — some of the highest levels of any type of fresh produce. Lycopene is a phytonutrient, which is a naturally occurring compound in fruits and vegetables that reacts with the human body to trigger healthy reactions. It is also the red pigment that gives watermelons, tomatoes, red grapefruits and guavas their color. 

Lycopene has been linked with heart health, bone health and prostate cancer prevention. It's also a powerful antioxidant thought to have anti-inflammatory properties, according to Victoria Jarzabkowski, a nutritionist with the Fitness Institute of Texas at The University of Texas at Austin.

To really maximize your lycopene intake, let your watermelon fully ripen. The redder your watermelon gets, the higher the concentration of lycopene becomes. Beta-carotene and phenolic antioxidant content also increase as the watermelon ripens. "Beta carotene is an antioxidant found in red-orange fruits and vegetables. It helps with immunity, skin, eye and the prevention of cancer," said Lemond.

A 2011 study in the Journal of Food Composition and Analysis that investigated five types of watermelon at four stages of ripening found that unripe watermelon with primarily white flesh has nearly zero beta-carotene. By the time it is fully red, the fruit has become an excellent source of the phytonutrient. 

That doesn't mean the red parts are the only good ones. "All parts of the watermelon are good. There are a lot of nutrients throughout," said Jarzabkowski. This includes the white flesh nearest the rind, which contains more of the amino acid citrulline than the flesh, according to a 2005 study in the Journal of Chromatography. 

Citrulline is a valuable amino acid that converts to the amino acid arginine. These amino acids promote blood flow, leading to cardiovascular health, improved circulation, and according to research at Texas A&M University, erectile dysfunction improvement (you'd probably have to eat a lot of the fruit to get a Viagra-like effect, though).

Recent studies have found that watermelon seeds are also wonderfully nutritious, especially if they are sprouted and shelled. They are high in protein, magnesium, vitamin B and good fats, according to an analysis by the International Journal of Nutrition and Food Sciences.  

Here are the nutrition facts for the watermelon, according to the U.S. Food and Drug Administration, which regulates food labeling through the National Labeling and Education Act:

Serving size: 2 cups diced (10 oz / 280 g)
Calories: 80 (Calories from Fat 0)

Amount per serving (and %DV*)
*Percent Daily Values (%DV) are based on a 2,000 calorie diet.

Total Fat: 0g (0%)

Total Carbohydrate: 21g (7%)
Dietary Fiber: 1g (4%)
Sugars: 20g

Cholesterol: 0mg (0%)
Sodium: 0mg (0%)
Potassium: 270mg (8%)
Protein: 1g

Vitamin A: (30%)
Vitamin C: (25%)
Calcium: (2%)
Iron: (4%)

Heart health

Watermelon's high levels of lycopene are very effective at protecting cells from damage and may help lower the risk of heart disease, according to a study at Purdue University. A study published in the American Journal of Hypertension found that watermelon extracts helped reduce hypertension and lower blood pressure in obese adults.

Watermelon may be especially important for older women. A study published in Menopause found that postmenopausal women, a group known to have increased aortic stiffness, who took watermelon extract for six weeks saw decreased blood pressure and arterial stiffness compared to those who did not take watermelon extract. The authors of the study attributed the benefits to citrulline and arginine. 

Arginine can help improve blood flow and may help reduce the accumulation of excess fat. 

Anti-inflammatory properties

"The lycopene in watermelon makes it an anti-inflammatory fruit," Jarzabkowski said. Lycopene is an inhibitor for various inflammatory processes and also works as an antioxidant to neutralize free radicals. Additionally, the watermelon contains choline, which helps keep chronic inflammation down, according to a 2006 article published in Shock medical journal.

Reducing inflammation isn't just good for people suffering from arthritis. "When you're sick, you have cellular damage, which can be caused by a variety of factors including stress, smoking, pollution, disease, and your body becomes inflamed," Jarzabkowski said. "It's called 'systemic inflammation.'" In this way, anti-inflammatory foods can help with overall immunity and general health. 

Hydration

"Watermelons help with overall hydration, and that is a great thing," said Lemond. "They say we can get 20-30 percent of our fluid needs through our diet alone, and foods like these certainly help." Additionally, their juice is full of good electrolytes. This can even help prevent heat stroke. 

Digestion

The watermelon contains fiber, which encourages a healthy digestive tract and helps keep you regular. 

Skin and hair benefits

Vitamin A is stellar for your skin, and just a cup of watermelon contains nearly one-quarter of your recommended daily intake of it. Vitamin A helps keep skin and hair moisturized, and it also encourages healthy growth of new collagen and elastin cells, according to the Cleveland Clinic. Vitamin C is also beneficial in this regard, as it promotes healthy collagen growth.

Muscle soreness & athletic performance

Watermelon-loving athletes are in luck: drinking watermelon juice before an intense workout helps reduce next-day muscle soreness and heart rate, according to a 2013 study published in the Journal of Agricultural and Food Chemistry. This can be attributed to watermelon's amino acids citrulline and arginine, which help improve circulation.

A 2015 study published in the Journal of Applied Physiology suggests that watermelon's citrulline may also help improve athletic performance. Study participants who took citrulline supplements saw a boosted performance with more power production in high-intensity exercise like cycling and sprinting. 

Cancer prevention

Like other fruits and vegetables, watermelons may be helpful in reducing the risk of cancer through their antioxidant properties. Lycopene in particular has been linked to reducing prostate cancer cell proliferation, according to the National Cancer Institute.

Health risks

If eaten in reasonable amounts, watermelons should produce no serious side effects. If you eat an abundance of the fruit daily, however, you may experience problems from having too much lycopene or potassium.

The consumption of more than 30 mg of lycopene daily could potentially cause nausea, diarrhea, indigestion and bloating, according to the American Cancer Society.

People with serious hyperkalemia, or too much potassium in their blood, should probably not consume more than about one cup of watermelon a day, which has less than 140 mg of potassium. According to the National Institutes of Health, hyperkalemia can result in irregular heartbeats and other cardiovascular problems, as well as reduced muscle control.

Loading up on water-dense foods like watermelon can be tempting for those looking to lose weight because they help you feel full, but Lemond cautions against going to extremes. "Eating more fruits and vegetables of any kind naturally helps decrease overall calories (energy) of the diet," she said. "We know that people that eat higher quantities of fruits and vegetables typically have healthier body weights However, I do not recommend eating only watermelon … You will lose weight, but that weight will be mostly muscle."

Jarzabkowski also warned watermelon lovers to be mindful of their sugar intake. "Though watermelon's sugar is naturally occurring, [watermelon] is still relatively high in sugar."

"My recommendation is always to vary your selections," said Lemond. "Watermelon is a great hydrating food, so keep it in along with other plant foods that offer other benefits.  Variety is always key."

Watermelon facts

Some fun facts about watermelons, from the National Watermelon Promotion Board and Science Kids

The watermelon (Citrullus lanatus) is related to cucumbers, pumpkins and squash.

The watermelon probably originated in the Kalahari Desert in Africa.

Egyptians placed watermelons in the burial tombs of kings to nourish them in the afterlife. The first recorded watermelon harvest is depicted in Egyptian hieroglyphics from about 5,000 years ago.

Merchants spread the use of watermelons along the Mediterranean Sea. By the 10th century, watermelons had found their way to China, which is now the world's top producer of watermelons.

The Moors in the 13th century brought watermelons to Europe.

The watermelon likely made its way to the United States with African slaves.

Early explorers used watermelons as canteens.

The first cookbook published in the United States in 1776 contained a recipe for watermelon rind pickles.

About 200 to 300 varieties are grown in the United States and Mexico, but only about 50 varieties are very popular.

By weight, watermelon is the most consumed melon in the United States, followed by cantaloupe and honeydew.

The watermelon is the official state vegetable of Oklahoma.

All parts of a watermelon can be eaten, even the rind.

Guinness World Records says the world's heaviest watermelon was grown by Lloyd Bright of Arkadelphia, Arkansas, in 2005. It weighed 268.8 lbs. (121.93 kg).

The United States ranks fifth in the worldwide production of watermelons. Forty-four states grow watermelons, with Florida, Texas, California, Georgia and Arizona leading the country in production.

A seedless watermelon is a sterile hybrid, which is created by crossing male pollen for a watermelon, containing 22 chromosomes per cell, with a female watermelon flower with 44 chromosomes per cell. When this seeded fruit matures, the small, white seed coats inside contain 33 chromosomes, rendering it sterile and incapable of producing seeds.