Surprising Side Effects of Eating Grapes, Dietitians Say: Eat This Not That

Did you know that grapes are one of the most popular fruits in America, right after strawberries and bananas? It’s not even that surprising. Grapes taste sweet like candy, make a handy portable snack since you don’t need any utensils, and are just plain fun to eat. Not to mention, they’re packed with a wide range of beneficial nutrients, so you can generally feel good about eating them.

According to Shirlene Reid, RD, MA, grapes, like any other fruit, are healthy as long as consumed in moderation. The only thing you really need to watch out for is the high sugar content, Reid says, which can quickly rise if you’re gobbling them up in large handfuls. Keep in mind that one serving is 1/2 cup (or about 16 grapes). You may also want to portion that portion in a plastic bag so you don’t get carried away.

But have you ever wondered how eating grapes could affect your body? Experts say there are both pros and cons to eating them. Here are some common side effects to be aware of.

green grapes

Are you trying to keep your brain in top condition as you age? So consider putting some grapes in your business lunch bag.

“Grapes improve memory and focus,” says Danielle McAvoy, RD with Strong Home Gym. “The antioxidant compounds in grapes help minimize oxidative stress in the brain. This protects the brain from cognitive decline and memory loss with age.”

Melissa Mitri, RD with Zenmaster Wellness, notes that grapes can also improve blood flow to the brain, thereby improving your daily focus.

Studies have shown that resveratrol, a specific antioxidant found primarily in grape skin, helps reduce the risk of Alzheimer’s by lowering inflammation in the brain and also eliminating beta-amyloid peptide, which has been linked to the progression of this full disease when it accumulates.


Chronic inflammation has been linked to cancer, heart disease, asthma, type 2 diabetes, and rheumatoid arthritis, among other conditions. Fortunately, grapes are packed with antioxidants like vitamin C, vitamin K, polyphenols, catechins, and anthocyanins, which can help reduce inflammation, says Jesse Feder, RD and personal trainer at Strength Warehouse.

“Also, grapes, especially red ones, are known to be rich in resveratrol,” adds Feder. “Research has shown that this compound protects against oxidative stress and inflammation.”

In particular, resveratrol provides a protective coating for blood vessels to prevent injury, thereby warding off inflammation of the heart.

woman harvesting grapes

When high blood pressure is not controlled, it can increase the risk for the two leading causes of death in Amercia: heart disease and stroke. But the good news is, there are many easy ways to treat and prevent high blood pressure. For one, McAvoy and Mitri suggest snacking on some grapes, which can help balance blood pressure because they’re high in potassium and low in sodium.

A 2016 study in Nutrients suggested that potassium helps lower blood pressure by helping to dilate veins and arteries while at the same time eliminating excess sodium.


Grapes make a great evening snack because they can help you fall asleep and capture some quality Z’s, says McAvoy. Why? This fruit contains a small amount of melatonin, the hormone that helps regulate your body’s sleep-wake cycle.

Try eating grapes an hour or two before bed and remember, pay attention to your serving size or you may accidentally overload the sugar, which can interfere with the quality of your sleep.

red and green grapes

If you’ve ever lost track of how much grapes you’ve eaten, which, let’s face it, is all too easy to do, you may have experienced a stomach ache. According to Reid, this usually happens due to the high amounts of fructose in grapes (around 12.4 grams per cup, compared to around 3 grams in a cup of raspberries).

“Fructose is a natural sugar found in fruit that can cause gas when consumed in high quantities,” says Reid. “So when you eat too many, you may get stomach pain from gas. The tannins in grapes can also play a role in stomach pain – these natural polyphenols, found in the peel and seeds, can cause nausea and diarrhea if ingested in large quantities. “

Mitri adds that some people who are especially sensitive to these compounds in grapes may experience bloating, constipation, or diarrhea after eating too many.

merlot grapes

Sara Chatfield, RDN at Health Canal, calls grapes one of her favorite snacks. This is partly due to the fact that this fruit is rich in vitamin C, beta carotene, quercetin, and other antioxidants known to promote immune health.

The stronger your immune system, the better prepared your body is to fight disease. How is this a reason to savor grapes during cold and flu season?

Leave a Comment