Over 90% water, and a better lycopene source than tomato.
Watermelon is around 92% water, which is most of what makes it useful. It is one of the
lowest-calorie fruits by weight and genuinely helpful for hydration in
heat.
Nutritionally its standout feature is lycopene — watermelon contains more
per gram than fresh tomato. It is also the best dietary source of citrulline, an amino acid
involved in blood vessel dilation, concentrated particularly in the white
rind.
Despite the sweetness, the sugar per portion is modest because there is so much
water diluting it.
Per 100g of flesh.
Based on the nutrients and fibre this food supplies. These are supporting foods, not treatments.
A ripe watermelon sounds hollow and has a large creamy-yellow field spot
where it sat on the ground. A white or pale spot means it was picked
early.
Heavy for its size means full of water, which is what you
want.
The white rind is edible and is where the citrulline
concentrates. Pickled or stir-fried, it is used across South Asia and the American
South.
Wash the outside before cutting. Melon rinds have been involved
in listeria and salmonella outbreaks; the knife carries surface bacteria into the flesh.
Lycopene is a carotenoid that is more bioavailable from watermelon than from raw tomato,
because it does not need cooking to be released.
Citrulline is converted in the kidneys
to arginine, which the body uses to make nitric oxide — the signal that relaxes blood
vessel walls. That is the mechanism behind watermelon's appearance in blood pressure research,
though the effect from ordinary portions is modest.
Food safety: pre-cut melon has been involved in listeria and salmonella
outbreaks. Buy whole where you can, wash the rind, refrigerate cut fruit promptly.
Diabetes: whole fruit over juice, portion aware, and better eaten
with protein or fat than alone.
IBS: several fruits are high-FODMAP
and commonly trigger symptoms — tolerance is personal.
Kidney
disease: potassium may need limiting. Ask your doctor for your numbers.
This is information, not a prescription. If you are managing a diagnosed condition or taking medication, talk to your doctor before making a large change to your diet.
Nutrition figures on this page come from standard food composition data. These links let you check the numbers and read the underlying research yourself rather than taking our word for it.