At a glance:
- 100 g of watermelon contains approximately 30 kcal, 0.6 g of protein and 7.5 g of carbohydrates.
- Watermelon contains an average of 4.5–7.5 mg of the antioxidant lycopene per 100 g — more than most tomato products.
- The amino acid citrulline in watermelon supports normal blood flow and helps lower blood pressure.
- Watermelon is over 91% water, making it one of the best natural sources of hydration.
Watermelon is a summer fruit whose nutritional value is often underestimated — behind its low calorie count lies a rich array of phytonutrients and amino acids. This article takes a systematic look at what 100 grams of watermelon actually offers your body.
What is the nutritional value of watermelon per 100 grams?
100 g of edible watermelon contains approximately 30 kcal, 7.5 g of carbohydrates (of which 6.2 g are naturally occurring sugars), 0.6 g of protein, 0.2 g of fat and 0.4 g of dietary fiber (National Institute for Health Development nutrition database, 2023). Water accounts for more than 91% of watermelon’s weight, making it an extremely low-energy-density food. It contains approximately 8 mg of vitamin C and 112 mg of potassium per 100 g.
Watermelon’s protein content is modest — to understand why protein is essential for your body, read What is protein?, which explains its role in cell structure and repair. If you train, it makes sense to combine watermelon with foods that are richer in protein: Egg nutrition provides a useful overview of why eggs, with their amino acid profile, are among the most complete sources of animal protein.
Which bioactive compounds does watermelon contain, and why do they matter?
Watermelon’s real nutritional strength lies in its micronutrients and phytonutrients.
Lycopene is a carotenoid that gives watermelon its bright red color. 100 g of watermelon contains an average of 4.5–7.5 mg of lycopene — generally more than fresh tomatoes (Edwards et al., 2003). Lycopene has been associated with reduced oxidative stress and support for cardiovascular health.
Citrulline is a non-essential amino acid found at particularly high levels in watermelon — in both the flesh and the rind (Rimando & Perkins-Veazie, 2005). Your body converts citrulline into arginine, which is used to produce nitric oxide — a vasodilator that relaxes blood vessels.
Vitamin C (approximately 8 mg/100 g) provides around 9% of an adult’s recommended daily intake, according to the EFSA Dietary Reference Values database.
As the article More than calories explains, a food’s value cannot be reduced to its energy content alone — this diversity of bioactive compounds is precisely what makes watermelon more than just a sweet snack.
How does the citrulline in watermelon affect blood pressure and athletic performance?
The effects of citrulline have been clinically documented. In a randomized pilot study, Figueroa et al. (2011) confirmed that consuming watermelon extract was associated with a significant reduction in systolic blood pressure in adults diagnosed with prehypertension. Collins et al. (2007) showed that eating watermelon significantly increases plasma L-arginine concentrations — suggesting potential benefits for blood flow and nitric oxide metabolism in muscles.
This is relevant for athletes: greater arginine availability supports vasodilation and may speed up recovery after exercise. However, watermelon does not replace complete protein sources — Egg nutrition explains why the amino acid profile of eggs is considered one of the most nutritionally valuable reference standards.
Is watermelon suitable if you are watching your weight, and how can you eat it sensibly?
Watermelon’s low energy density (30 kcal/100 g) and high water content make it a suitable choice whether you are on a diet or lead an active lifestyle. Although its glycemic index is 72, the glycemic load of a standard serving (120 g) is only 4 — meaning the rise in blood sugar is moderate and the insulin response is modest.
Overall, watermelon is low in calories yet rich in lycopene, citrulline and vitamin C — a good choice for everyday eating, hydration and recovery after exercise.
References
- Edwards AJ, Vinyard BT, Wiley ER, et al. (2003). Consumption of watermelon juice increases plasma concentrations of lycopene and beta-carotene in humans. J Nutr. 133(4):1043–50. PMID: 12612176
- Figueroa A, Sanchez-Gonzalez MA, Perkins-Veazie PM, Arjmandi BH. (2011). Effects of watermelon supplementation on aortic blood pressure and wave reflection in individuals with prehypertension: a pilot study. Am J Hypertens. 24(1):40–4. PMID: 21849873
- Rimando AM, Perkins-Veazie PM. (2005). Determination of citrulline in watermelon rind. J Chromatogr A. 1078(1–2):196–200. PMID: 15862547
- Collins JK, Wu G, Perkins-Veazie P, et al. (2007). Watermelon consumption increases plasma arginine concentrations in adults. Nutrition. 23(3):261–6. PMID: 17352962
- EFSA (2019). Dietary Reference Values for the EU. European Food Safety Authority.
Frequently asked questions
How many calories are in watermelon?
100 grams of watermelon contains approximately 30 kcal. A typical 200–300 g serving therefore provides 60–90 kcal, making watermelon one of the least energy-dense fruit choices.
Does watermelon contain protein?
Watermelon contains 0.6 g of protein per 100 g — a small amount. Watermelon is not suitable as a primary protein source, but combined with eggs, quark or legumes, it can make a useful contribution to meeting your protein needs.
What is citrulline, and why is it valued in watermelon?
Citrulline is an amino acid found at unusually high levels in watermelon. Your body converts it into arginine and then into nitric oxide, which supports normal blood flow and blood pressure.
Does watermelon contain more lycopene than tomatoes?
Yes — 100 g of raw watermelon contains an average of 4.5–7.5 mg of lycopene, exceeding the amount in most fresh tomatoes (2–3 mg/100 g). Lycopene is an antioxidant associated with supporting cardiovascular health.
Is watermelon suitable for people with diabetes?
Watermelon has a glycemic index of 72, but the glycemic load of a standard serving is low (around 4) because the amount of sugar per serving is small. Consult your doctor before making dietary decisions.
Illustrative photo: Mart Veelmaa
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