Fruits like watermelon are an essential part of a healthy diet, as they’re packed with vitamins, minerals, and healthy antioxidants.

Watermelon is a great source of vitamins A and C, as well as the antioxidant lycopene, which is revered for its cancer-fighting properties and cardiovascular health benefits (1, 2, 3).

However, you may be wary of overeating fruit. Overeating anything — including fruits — may come with a couple of unwanted side effects.

This article focuses on the side effects of eating too much watermelon and dispels certain myths about watermelon’s effect on your diet.

Despite its multiple health benefits, there are some downsides to overeating watermelon.

May cause digestive issues

Eating too much watermelon may cause abdominal discomfort, bloating, gas, and diarrhea due to its high FODMAP content (4, 5, 6).

FODMAP is an acronym that refers to a group of fermentable short-chain carbs that are either nondigestible or slowly absorbed in the small intestine. These include oligosaccharides, disaccharides, monosaccharides, and polyols (5).

Nutritionists generally prescribe low FODMAP diets for people with irritable bowel syndrome (IBS), a digestive condition characterized by symptoms like bloating, gas, and diarrhea (7).

Yet, high FODMAP intakes may also cause IBS-like symptoms and aggravate gastroesophageal reflux (GERD) in healthy people without IBS (4, 5).

Nutritionists deem watermelon a high FODMAP food because of its fructose content. Fructose is a monosaccharide — or a simple sugar — that may cause bloating or discomfort when consumed in large amounts (5).

While watermelon’s high FODMAP status may indicate it causes digestive issues among fructose-sensitive people, you shouldn’t expect a stomach ache every time you eat a large serving. Still, those who suffer from IBS may want to eat watermelon more sparingly.

May raise your blood sugar levels

In addition to its high FODMAP content, watermelon has a high glycemic index (GI). Therefore, overeating watermelon may raise your blood sugar levels, which you should be particularly mindful of if you have diabetes.

The GI of a food measures its effects on your blood sugar during a 2-hour period. High GI foods tend to spike your blood sugar levels, while low GI foods produce a steady rise (8, 9).

Foods classified as low GI have a GI level under 55, those deemed to be medium GI range from 56–69, and high GI foods are over 70. Watermelons have a GI of 72–80 (10, 11).

Nevertheless, while the GI may indicate how your blood sugar reacts to a specific carb-containing food, the glycemic load (GL) considers the serving size (8, 9).

As such, the GL tends to be a more accurate measure of a food’s effect on your blood sugar levels.

The GL index also classifies foods into low, medium, or high. A count of less than 10 is considered low, 11–19 is medium, and over 20 is considered high (10).

With a GL of 5–6 per cup (152 grams), watermelons are classified as a low GL food — meaning that regardless of their high GI status, a small, 1-cup (152-gram) serving won’t cause any harm (11).

However, overeating watermelon will increase its GL, most likely leading to a spike in your blood sugar levels.

Watching your blood sugar is especially important if you have diabetes (12).

May lead to orange discoloration of the skin

Although rare, one study determined that eating too much watermelon may be correlated with a yellow-orange discoloration of the skin called lycopenemia, a variant of carotenemia (13).

Lycopene is both an antioxidant and a pigment, and it’s responsible for the characteristic red color of watermelons and other fruits and vegetables.

If consumed in excess, lycopene may build up in your skin’s outer layers and alter your skin pigmentation. However, the study didn’t indicate how much was too much watermelon in this case (13).

Fortunately, lycopenaemia is a rare condition that’s entirely reversible. Its effect on your skin can be completely reversed by reducing heavy intake of lycopene-rich foods like watermelon.

Summary

Eating too much watermelon may cause abdominal discomfort, bloating, gas, a spike in your blood sugar levels, and — in rare cases — an orange discoloration of your skin.

Overeating watermelon may present you with some unforeseen side effects. However, some side effects you may have heard are completely unfounded.

Some dubious sources claim overeating watermelon may lead to heart problems and overhydration. Neither claim is backed by science or likely to occur.

What’s more, dubious claims have been made alleging that watermelon’s potassium content may cause hyperkalemia. This condition is characterized by a slow heart rate, low blood pressure, muscle weakness, and an irregular heartbeat.

Yet, you’d have to eat a whole watermelon to exceed the recommended amount of potassium you should consume per day. Even so, research agrees that in people without kidney disease, your body adapts and excretes excess potassium through urine (14).

Nevertheless, people with heart failure, kidney disease, type 1 diabetes, adrenal insufficiency, and liver disease may have a hard time managing excess potassium (15).

Others have made claims about the dangers of overhydration — an imbalance of fluids that may dilute electrolytes in your blood — since watermelons comprise 92% water. However, there’s no research to back this claim.

Summary

Overeating watermelon is very unlikely to cause overhydration or heart problems in healthy people. Yet, people with heart failure, kidney disease, type 1 diabetes, adrenal insufficiency, and liver disease are at higher risk of developing heart problems.

You may want to indulge in sweet and refreshing watermelon on a hot summer day.

Fortunately, watermelon is a safe and healthy fruit, and nutritionists have not defined an unsafe limit for its intake. You may only want to moderate your intake if you need to keep your blood sugar levels low.

Regarding its effect on blood sugar levels, a 4-cup (608-gram) serving of watermelon has a high glycemic index level and provides 46 grams of carbs, with 36 of those grams coming from sugar. This may cause a spike in your blood sugar levels (16).

If you want to stay on the safe side of sugar intake, the U.S. Department of Agriculture (USDA) recommends eating about 2 cups of fruit per day for those on a standard 2,000-calorie diet, which translates to roughly 300 grams in the case of watermelon (17).

Summary

There’s no official upper limit for watermelon intake. However, try to limit your intake to 2 cups (300 grams) a day if you’re not consuming other fruits.

Watermelons are a healthy and refreshing fruit, but eating too much may lead to high blood sugar levels or gastrointestinal discomfort among those who are sensitive to FODMAPs.

As with anything else in nutrition, moderation is key. Try to limit your watermelon intake to 2 cups (300 grams) per day if that’s the only fruit you’ll be having.