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   Apr 25

High blood pressure? Try watermelon juice

Fancy a nice slice of watermelon? It’s so much more than a refreshing snack on a warm day. Research is increasingly showing that it has surprising health benefits too — ranging from beating post-workout muscle soreness to potentially lowering blood pressure.

A team at Reading University is the latest to investigate its benefits, with a study into the impact of watermelon juice on blood pressure. Dr Charlotte Mills, a lecturer in nutritional sciences, has recruited ten young, healthy adults for a trial that involves the volunteers having blood-pressure measurements taken before drinking half a litre of a commercial watermelon juice or a placebo drink of water, and again after drinking.

She says she is looking to find out if the compound L-citrulline, found naturally in watermelon, helps to widen blood vessels and lower blood pressure. “Watermelons are such lovely fruit, but there has also been a lot of recent scientific interest in their potential health benefits,” Mills says. “We know L-citrulline has the potential to lead to dilation of blood vessels and we want to find out if there is enough of it in watermelon juice to make a difference.”

Previous studies suggest that this may be so. At Florida State University, a team gave overweight middle-aged men and women a placebo or an extract of watermelon for six weeks before asking them to switch. During that time the participants had their blood pressure checked in normal conditions and with one hand dipped repeatedly in cold water — cool temperatures are a source of stress that cause blood pressure to increase and the heart to work harder. The results of that study showed that the watermelon extract had a positive impact on blood pressure and the heart.

It’s not just blood pressure that can benefit from watermelon. In 2019 a pair of papers hailed it as being among the healthiest fruit. Researchers from the University of South Africa highlighted that “it contains vitamins B, C, E and phytochemicals such as polyphenols and betacarotene and so possesses anti-inflammatory and antioxidant properties”.

“Watermelons are also a source of lycopene, a carotenoid that gives them their pink colour, and that has been shown to help to keep the prostate gland healthy,” says the nutrition therapist Ian Marber.

No wonder, then, that watermelon juice suddenly seems to be everywhere — brands including Mello and What a Melon, and Vitamin Planet’s watermelon juice are on sale in supermarkets, while roasted watermelon seeds — high in fibre, protein, iron, magnesium and potassium — are available in health food stores such as Holland and Barrett.

At San Diego State University, exercise and nutrition scientists found that fresh watermelon can help to ward off hunger pangs and help with weight loss. They gave 33 overweight adults 300g of watermelon cubes or low-fat cookies as a daily snack for four weeks. Not only did the watermelon eaters have a lower BMI and waist-to-height ratio by the end of the trial, they also reported feeling less hungry for up to 90 minutes after eating the fruit, compared with the cookie-eaters, whose hunger levels returned after 20 minutes. Although the fruit contained almost double the amount of sugar (17g) as the cookies (9g) per serving, the scientists said that “watermelons possess nutritional components that suppress a rise in glucose and also contain a small amount of fibre, which can improve the body’s glucose tolerance”. All of this meant that the rise and fall of blood sugar that can increase appetite was less pronounced than expected.

Because it is 92 per cent water — and therefore great for rehydrating — watermelon is also an ideal post-workout snack and may even enhance performance, according to studies. When exercisers were given natural watermelon juice, watermelon juice enriched with added L-citrulline or a placebo an hour before their workouts, researchers from the Technical University of Cartagena in Spain found both types of the fruit juice “helped to reduce the recovery heart rate and muscle soreness after 24 hours”, although it was the natural watermelon juice that seemed to be more easily absorbed by the body.

Another trial at Exeter University showed that after two weeks of taking a watermelon juice concentrate, which provided 3.4g L-citrulline, or an apple juice placebo, cyclists experienced improved muscle oxygenation during moderate-intensity exercise, although in this case there was no improvement in performance. “Watermelon juice typically contains about 2.3g citrulline per litre so you’d need to drink about 2.5 litres of juice to get the dose of citrulline used in some studies,” says the sports nutritionist Anita Bean, author of The Complete Guide to Sports Nutrition. “Perhaps the next fashionable health tonic for gym-goers will be a concentrated watermelon shot.”

Source: Sunday Times

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