Watermelon is generally considered as a fruit and belongs to a plant family called Cucurbitaceae.
The fruit is native to the Kalahari desert of Africa but is now also harvested in many tropical regions of the world.
Hence the name, watermelon is predominantly comprised of water (~92%), with a small amount of carbohydrates in the form of sugar (~8%). This is why watermelon is a very low-calorie food, providing just 30 calories per 100 grams.
Other than this, watermelon is a valued source of natural antioxidants with special reference to lycopene, ascorbic acid, and citrulline.
In particular, lycopene is the main component that is responsible for watermelons therapeutic use. Lycopene is best characterized for its distinctive red color in fruits and vegetables such as tomatoes.
1. Defends Against Cellular Damage
Lycopene can significantly reduce oxidative stress, defined as a disturbance in the balance between the production of free radicals and antioxidant defenses .
This is one of the reasons why lycopene is shown to significantly reduce the oxidation of LDL-cholesterol and prevent blood vessel damage 
This substance may also protect against damage to DNA and have a specific role on inhibiting cancer growth . This is due to an alteration in gene function in a manner which can positively affect carcinogenic metabolism .
2. Helps You To Hydrate
Drinking water is required to keep your body well-hydrated, however eating foods with a high water content can also contribute towards daily fluid recommendations – approximately half a gallon.
Amazingly, watermelon is comprised of 92% water. Yes, there is just an 8% difference between a watermelon and a glass of water. Based on this, a bowl of watermelon can be just as effective for hydration purposes as drinking a glass of water – great for anyone who really hates water!
3. May Help Decrease Cancer Risk
Administration of lycopene at early stages of cancer may have the ability to slow down cancer cell progression .
In fact, diets high in lycopene have a ~25% reduced incidence of prostate cancer and up to a ~45% reduced risk of other cancers .
There may also be a particularly positive influence of lycopene on aerodigestive tract cancers; oral cavity, pharynx, larynx and esophagus .
Although the physiological mechanisms are not clear, lycopene has some metabolic influence on reducing the growth of tumors . It is speculated that lycopene interferes with the mutation process of DNA and the spread of a tumor from its primary site by directly activating the genes that can inhibit mutations  .
The fact that lycopene is a strong antioxidant likely attributes to its antiproliferative effects against cancer.
4. May Lower Cholesterol Levels
Dietary lycopene can exert cardioprotective effects due to its high antioxidant activity .
At least in animals, diets incorporating lycopene mitigate the signs and symptoms of high cholesterol levels.
Some data has revealed that lycopene may potentially suppress cholesterol synthesis, and also enhance the clearance of LDL from the blood. Lycopene has even been referred to as a “hypocholesterolemic agent” .
Watermelon specifically could be very advantageous for lowering cholesterol levels as the bioavailability of lycopene is relatively high .
5. Potential To Reduce Diabetes Risk
Phenolic compounds such as lycopene have long been known for their hypoglycemic action.
Specifically, daily consumption of lycopene can reduce serum glucose levels ~5% .
However, it is noted that the amount of lycopene needed for this effect is significantly more than what can be realistically obtained through watermelon alone.
6. Can Help Aid Weight Loss
A helpful tactic when trying to lose weight is to incorporate foods that have a low-calorie content relative to the volume of food, as this can help to increase satiation and essentially ‘trick’ the brain into thinking that more food is being taken on board than there actually is.
Watermelon is perfect for this, containing just 30 calories per 100 gram serving.
In fact, an entire large watermelon contains only around 1000 calories, likely enough to help keep anyone full throughout the day (not that I advise eating a whole watermelon!).
The high water content of watermelon may also help an individual feel full, especially when combined with a high dietary fiber intake which this fruit can also contribute towards.
Watermelon is a fruit with an extremely high water content, that also contains health-promoting substances such as lycopene.
Lycopene has shown in many studies to potentially fight cell damage, decrease cancer risk, lower cholesterol levels, and reduce the risk of type 2 diabetes.
The large amount of water in watermelon could also make it useful for hydration purposes and for keeping satiated.