Watermelon contains mostly water (91%) and almost no protein and fat. They are low in calories and contain a small amount of fiber and carbohydrates.
Watermelons are a great source of vitamin C. They are also a good source of potassium, copper, pantothenic acid (B5), magnesium and beta-carotene.
They are a great source of citrulline and lycopene. Citrulline is an amino acid that is converted to arginine. Both citrulline and arginine are involved in nitric oxide synthesis, which reduces blood pressure and accelerates wound healing. It is the nitric oxide that reduces blood pressure and has shown some promise relieving erectile dysfunction.
Watermelon is the best known fresh source of lycopene. Lycopene is a powerful antioxidant, most commonly associated with tomatoes. Watermelon has almost 1.5 times the amount of lycopene than a tomato. It is lycopene that gives watermelon their characteristic pink color.
Consuming watermelon has also been shown to improve insulin sensitivity and decrease muscle soreness following exercise.
Watermelon is also anti-inflammatory. This is due to the abundance of lycopene, cucurbitacin E, tripterpenoid. These phytochemicals decrease inflammation by reducing the enzyme cycloxigenase. This is the same mechanism by which NSAIDS (ibuprofen, aspirin, celebrex) work.
Many people do not know that the rind it edible. In fact, it contains a ton of chlorophyll and even more citrulline than the flesh.