Is the Watermelon Diet Worth Trying?

Here's what you need to know about the diet that focuses on just one food.


Paleo, Whole 30, and even plant-based keto. These days, there are no shortage of diets for us to cling onto for all our health hopes. This world of diets includes one newly popular one, centred around one favourite food: watermelon.

A certain cheerleader named Gabi Butler on the Netflix hit docuseries Cheer boasted about going on the watermelon diet leading to a stir on social media and leaving some people wondering if it’s worth checking out. (She talks about it as a watermelon “fast” in an interview with Extra.)

Like many other aggressive diets, the watermelon diet makes some big promises. But does it deliver?

Obviously, any diet that only involves eating one food for a certain period is going to get alarm bells ringing. So we chatted to a dietitian for the lowdown on the watermelon diet to figure out if it’s just another fad or one that can give your health and your running the boost they need.

What precisely is the watermelon diet?

Imagine eating a crisp, juicy slice of watermelon on a hot summer’s day after a steamy run. Now, imagine eating nothing but watermelon, morning to night. That is the gist of the so-called watermelon diet.

There are a few variations on ways to do it that are floating around, but most often someone will eat no other calories than those hailing from watermelon for a certain number of days, and then start to introduce more foods into the diet. For example, you may begin introducing other foods back into your life by having two light meals each day and eat watermelon as a snack before returning to your regular eating schedule. But some people just resume their regular diet from the get-go after their ‘cleanse.’

The watermelon-only stage generally does not last more than a week, and can be as little as three days, but may reach up to 10 days for some die-hards. There are not any strict rules about how much watermelon you’re supposed to eat, but for many people, it may end up being about one fruit per day.

Why? The big sales pitch is that it can help you lose weight, reduce inflammation, and cleanse your body of harmful toxins—or at least that’s what a handful of influencers would have you believe. These types of diets inevitably appeal to people because they have a lot of structure but only require a short commitment period. And who doesn’t love eating watermelon? It would be a tougher sell if it was called the Sardine Diet.

Is the watermelon diet worth trying?

Before you go stock up on watermelons, though, dietitian and marathon runner Anne Mauney, M.P.H., R.D., offers some words of warning about this detox plan.

The main downside she tells Runner’s World is that by eating only a single food item, you won’t get a sufficient balance of macronutrients—that means carbohydrates, fat, and protein. “[Macronutrients are] essential for everyone, but especially for runners,” Mauney says.

Though you get some carbs from the watermelon, she stresses the diet is devoid of protein and fat, and in turn, an adequate amount of calories. “Not fuelling adequately means your body will not be able to sufficiently recover from workouts because your muscles can only adequately repair and re-build after long runs if your body has enough energy to do so.”

Over time, too large of an energy deficiency can lead to negative consequences such as nutrient deficiencies, fatigue, muscle loss, and hormonal issues, just to name a few. And with no gas in the tank, you’ll certainly have to scale back on your workouts during the watermelon-only phase of the diet. Your body just won’t have the energy to push through miles.

What’s more: You also run the risk of stomach woes from eating all that fruit, thanks to the fructose content, which can cause bloating and even diarrhea in some people.

Since watermelon is so high in water, proponents say that this helps keep hunger in check in the absence of a reasonable amount of calories. But this will quickly subside and soon you’ll likely find yourself ravenous, which could leave you going to town on an entire bag of chips or other foods with empty calories, which goes against the purpose of the diet.

As for cleansing the body, nutrition experts like Mauney are quick to point out that no food item will flush toxins from your system. Your body already has a natural detoxification system thanks to your liver and kidneys, and focusing on one particular food like watermelon is not going to impact that.

Plus, when you go back to eating your regular diet, it is very likely you’ll just put back on any weight you lost. You might end up gaining weight once you return to a normal diet if you end up overeating to make up for the previous restriction. Also, if you rarely ate fruits, veggies, and whole grains and didn’t have a balanced diet before doing the watermelon cleanse and go right back to it after, you certainly won’t be any further ahead when it comes to your health.

To be fair, if you’re generally healthy, it’s unlikely that following the watermelon diet for a few days will cause harm when it comes to longterm health consequences and nutritional deficiencies. If you have a plan for how to continue healthy eating efforts once the diet is over, and all you need is a little jumpstart, then maybe you explore it. But it’s never the best choice to eat a diet that focuses solely on one food. Instead, make small changes to create a bigger impact on your health.

But, what about the benefits of eating watermelon?

Just because the watermelon diet is a dud, doesn’t mean you shouldn’t consider wedging more of this fruit into your diet.

For starters, since the blushed fruit is about 90 percent water, Mauney says it can help runners meet their overall hydration needs. It’s not just the fluid you drink but also the fluids you get from certain foods like water-logged fruits that can contribute to daily hydration. And because watermelon has a mere 46 calories per 1-cup serving, you can eat plenty of it to help top up your fluid stores without too much worry about going overboard on calories.

Watermelon also contains vitamin C, beta-carotene, and the carotenoid phytochemical called lycopene. Lycopene is a red pigment that occurs naturally in certain plant tissues and can provide us with various health benefits. A meta-analysis of research conducted by British investigators found that higher intakes of lycopene and greater levels in the blood may offer some protection against mortality, stroke, and heart disease.

Meanwhile, a recent study in the journal Public Health Nutrition found that lycopene intake is inversely related to the risk of death from various cancers. Lycopene has also been well-studied regarding its inhibitory role in the progression of prostate cancer, specifically. To top off lycopene’s benefits, a few studies, including one from The Journal of Nutrition, suggest lycopene can help protect against cognitive decline as we age.

Lycopene acts as a powerful antioxidant which is likely how it benefits our health. Such antioxidants can scavenge cell-damaging reactive oxygen species to render them less harmful. This can lower levels of oxidative cell damage and inflammation in the body and, in turn, lower the risk for several chronic conditions, like cancer and heart disease.

Worth noting is that watermelon appears to contain even more lycopene than tomatoes. And research in The Journal of Nutrition shows that the bioavailability (i.e. how much we can absorb and use) of the lycopene in watermelon is very high. Levels can vary based on the type of watermelon with seedless varieties testing for higher lycopene amounts than seeded types.

Watermelon is also a source of citrulline, an amino acid that may have a positive impact on exercise performance. While you can make citrulline in your body, you can increase your levels by eating foods like watermelon that provide the amino acid. Citrulline can help widen your blood vessels by increasing levels of another amino acid, arginine, which then raises levels of the vasodilating compound, known as nitric oxide, that relaxes and widens arteries or veins to improve blood flow.

Due to its ability to boost blood flow, several studies have looked at citrulline in the context of endurance exercise performance. The increased oxygenation of muscles and glucose delivery to working muscles resulting from improved blood flow has been shown to improve performance, shown by metrics like increasing time to exhaustion by making the body more efficient at generating energy at a given work rate.

A study in the Journal of Sport and Health Science even found that citrulline supplementation may help reduce post-exercise muscle soreness, a benefit we can surmise is also chalked-up to better blood flow. The improvement in how blood flows through the body is likely why research shows increased citrulline consumption may help improve blood pressure numbers, which could have cardiovascular benefits in those with hypertension.

But how much watermelon you need to eat to get enough citrulline to boost your running and for how many days you need to eat it before a workout for it to have an ergogenic effect is not well known. A single dose of citrulline from watermelon juice does not appear to be beneficial for performance, which suggests that you need to consistently take in more citrulline.

Watermelon Diet: The Bottom Line

Watermelon can, of course, be part of a healthy, balanced diet considering its many nutritional benefits—not to mention it’s ultra-refreshing after a sweaty workout. But eating watermelon, or any single food item, alone is not an overall healthy approach to eating. There are smarter ways to approach eating for health, weight loss, and performance than such crash diets that research rarely finds have lasting results.

“If you’re looking to better nourish your body and want an approach that is sustainable longterm, I’d recommend focusing on an ‘add rather than subtract’ approach,” says Mauney. “So rather than subtracting too many things from your diet, which is not sustainable longterm, try putting a positive spin on it and adding in healthy items instead.” That could be an extra serving of vegetables at lunch or a wedge of watermelon for a satisfying afternoon snack.


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