Few foods capture the feeling of summer quite like a thick, juicy slice of watermelon — especially when it is eaten by the sea.
People have been eating watermelon for around 5,000 years, and the fruit is prized not only for its sweet flavour and crisp texture, but also for its high water content.
Much like cucumber and celery, it is often described as a way of “eating your water.”
“Watermelon is made up of around 92 per cent water, so it can be a useful and enjoyable way to support hydration,” says workplace wellness nutritionist Lily Soutter.
She adds, however, that there is no strong scientific evidence showing watermelon is more beneficial for hydration than simply drinking water.
A cup of diced watermelon — about 152g, or roughly a slice — contains around 46 calories and 9g of sugar, making it a relatively healthy option for those looking to satisfy a sweet craving.
Its red flesh is also rich in lycopene, the antioxidant responsible for its colour, and contains more of the compound per serving than any other fresh fruit or vegetable. Lycopene has been linked to reduced inflammation and improved heart health.
With that in mind, we examined the science behind some of the most common claims about watermelon, and asked our expert to dispel the biggest myths surrounding the striped green fruit.
Watermelon is made up of around 92 per cent water
Can watermelon ward off cancer?
A cup of diced watermelon contains around 12g of carbohydrates, virtually no fat or salt, and approximately 7mg to 11mg of lycopene.
Lycopene is the natural pigment that gives watermelon its red colour and is also found in foods including tomatoes and pink grapefruit.
It acts as an antioxidant, helping to neutralise unstable molecules known as free radicals.
Free radicals are produced naturally by the body, but levels can also rise because of factors such as smoking, air pollution and exposure to ultraviolet light.
In excessive amounts, they can damage cells and have been linked to ageing and a range of chronic diseases.
‘Fresh watermelon has a higher concentration of lycopene than fresh tomatoes,’ says Ms Soutter.
‘However, the lycopene in processed tomato products, such as canned tomatoes and tomato purée, tends to be more easily absorbed by the body than that found in fresh watermelon or raw tomatoes.’
Some studies have associated a higher intake of lycopene with a lower risk of prostate cancer. However, the findings have been inconsistent and do not prove that lycopene itself prevents the disease.
‘Lycopene is responsible for watermelon’s red pigment and has powerful antioxidant effects,’ says Ms Soutter.
‘There has been research into whether lycopene could reduce the risk of certain cancers, including prostate cancer, but the findings remain inconclusive.
‘More generally, eating a diet rich in fruit and vegetables, including watermelon, can support overall health and is associated with a lower risk of some cancers.’
And what about blood pressure?
A cup of watermelon contains several hundred milligrams of L-citrulline, an amino acid the body uses to produce nitric oxide.
Nitric oxide helps blood vessels relax and widen, supporting healthy circulation and potentially helping to regulate blood pressure.
‘Most research to date has assessed L-citrulline supplements, which provide a much higher dose of the amino acid than you would obtain from eating watermelon alone,’ says Ms Soutter.
A recent review of previous studies also found that consuming between 5mg and 30mg of tomato-derived lycopene a day – equivalent to a generous serving of watermelon or one or two tomatoes – was associated with modest improvements in cardiovascular risk factors, particularly blood pressure.
However, the findings relate largely to tomatoes and lycopene supplements, so they do not prove that eating watermelon will produce the same effect.
Watermelon contains L-citrulline, which plays a role in blood vessel relaxation and may support healthy blood pressure. Pictured, pop art legend Andy Warhol and music icon Tina Turner
Is it better to eat watermelon whole or juiced?
A small study from Louisiana State University investigated whether watermelon juice could help protect blood-vessel function during a temporary rise in blood sugar.
In the trial, 18 healthy young adults drank watermelon juice daily for two weeks.
The results suggested that it helped limit some of the temporary decline in blood-vessel function caused by raised blood sugar and influenced measures of heart-rate variability. However, the study was small, and more research is needed before firm conclusions can be drawn.
A cup of watermelon also provides Vitamin A, which helps support the immune system and maintain healthy skin and vision.
It contains around 12mg of Vitamin C, which helps protect cells from damage and supports the body’s natural defences, as well as approximately 170mg of potassium, a mineral involved in muscle function and fluid balance.
However, Ms Soutter says there is one key reason why a slice is generally preferable to a glass of juice: fibre.
‘Whole watermelon would be the first choice because it is more filling, retains its fibre and takes longer to consume than watermelon juice,’ she explains.
‘When fruit is juiced, much of the fibre is removed and its naturally occurring sugars are classed as free sugars, which should be limited in the diet. This is why current guidance recommends consuming no more than 150ml of fruit juice or smoothies a day.’
Who shouldn’t eat watermelon?
Watermelon is unlikely to cause serious problems with medicines, but eating very large amounts may add to the effects of blood-pressure drugs, nitrates, erectile-dysfunction medicines or potassium-sparing diuretics.
This could potentially lead to low blood pressure or, in people taking medicines such as spironolactone, raised potassium levels.
‘Whilst watermelon can be part of a diabetic-friendly diet, as it is a source of sugar, portion size would matter,’ says Ms Soutter.
Similarly, watermelon contains fructose; therefore, those with Irritable Bowel Syndrome (IBS) may want to be mindful of portion size if they notice it contributes to symptoms.
Plus, it goes without saying that anyone with a watermelon allergy should avoid it.
Can watermelon help with weight loss?
Some research suggests that replacing a less nutritious snack with watermelon could help people feel fuller and support weight management.
Fashion icon Victoria Beckham, 52, is known for her strict diet and exercise regime, was known in the past to only allow herself a watermelon cake on her birthday. Pictured in 2018
Kate Middleton reportedly enjoys a watermelon and feta salad in the summer
A small 2019 study followed 33 adults who were overweight or obese.
For four weeks, participants ate two cups of watermelon each day; during another four-week period, they consumed an equal-calorie portion of low-fat biscuits.
Participants reported feeling less hungry and fuller after eating the watermelon. They also experienced small reductions in body weight, body mass index and systolic blood pressure during the watermelon period.
However, the study was small and does not show that watermelon directly causes weight loss. The benefits may partly have arisen because it replaced a more calorie-dense, less filling snack.
A separate 2023 study also highlighted the weight loss benefits.
It involved children aged 10 to 17 years who drank a cup of blended watermelon every day for eight weeks and then drank a sugary drink with the same number of calories for the same period.
Results showed that drinking watermelon juice led to mild improvements in body fat and overall weight.
What is the best way to add watermelon to my diet?
Watermelon can be surprisingly versatile – and even makes a great addition to a salad.
Kate Middleton famously enjoys a watermelon and feta salad on hot summer days, with other popular recipes suggesting pairing the vibrant red flesh with salty, freshly fried halloumi or chargrilled prawns.
Victoria Beckham once revealed that in lieu of a carb-heavy birthday cake, she enjoyed a carved square of watermelon.
