Blueberries pack a hefty nutritional punch, being high in fiber, potassium and vitamins A, C and K. The nutrition in blueberries makes them a great option for snacking or topping your bowl of cereal or yogurt.
And we can't forget the other health benefits of blueberries, like potentially lowering blood pressure and helping to manage cholesterol and blood sugar, according to the Cleveland Clinic. Blueberries are also linked to healthy aging and better brain health.
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But can you overdose on blueberries? And what happens if you eat too many?
In some cases, the side effects of blueberries can include gastrointestinal distress, hypoglycemia and an increased risk of bleeding if you're taking certain prescription medications, says Alex McDonald, MD, a family physician with the American Academy of Family Physicians.
Here's a deeper look at what can happen if you eat a lot of blueberries along with the recommended serving size to stick with.
1. Bloating, Gas and Other GI Symptoms
Blueberries are high in fiber. According to the USDA, a 1-cup serving of blueberries has 84 calories and 3.6 grams of fiber.
The general recommended amount of fiber for adults is between 25 and 38 grams per day (or 14 grams for every 1,000 calories eaten), according to the Mayo Clinic. When eaten in moderate amounts, blueberries can help you reach that goal.
The Mayo Clinic recommends increasing the fiber in your diet gradually and drinking lots of water to help your body better process the nutrient.
Eating a lot of blueberries may change the color of your poop to dark blue or even black. But don't worry — your stool should return to normal once the fruit passes through your system.
2. Risk of Blood Clots
If you take certain medications, it may be a bad idea to eat too many blueberries. Blueberries are high in vitamin K, according to Mount Sinai, so consuming a lot of them can up your risk of blood clots if you take anticoagulants ("blood thinners") such as heparin or warfarin.
Vitamin K affects several important functions in the body, including regulating blood clotting and maintaining bone density. According to the National Institutes of Health, a 1 cup serving of blueberries contain 28 micrograms of vitamin K.
People who take prescription blood thinners are generally encouraged to keep bloodstream levels of vitamin K the same from day to day, per University of Michigan Health. Suddenly increasing or decreasing your intake of foods rich in vitamin K (i.e. many fruits and veggies) can lead to an increased risk of blood clots or bleeding, respectively.
If you plan to make any big changes to your fruit or veggie intake, talk to your doctor so they can determine if your blood thinner medication dosage needs to be adjusted.
3. Teeth Stains
There are plenty of drinks that can stain your teeth, like coffee, tea and wine, but blueberries are a common culprit, too, according to the American Dental Association (ADA). This is because of their intense pigmentation.
No matter if you eat blueberries fresh, frozen, juiced or preserved in jelly or jam, the deep-blue hue can discolor your tooth enamel or white fillings.
According to the ADA, it may be possible to combat the staining effect by brushing your teeth after eating blueberries. You can also rinse your mouth with water.
One of the health benefits of eating blueberries is the potential to lower blood sugar levels. But this could potentially be a negative side effect for someone taking diabetes medication. The interaction between blueberries and certain medication can result in hypoglycemia, Dr. McDonald says, although the research in this area is limited.
"There have been some animal studies demonstrating lower blood sugar with high level of blueberry extract, however, it is unclear how this affects people," he says.
Apart from some rare instances, eating too many blueberries is unlikely to cause major issues with your blood sugar. Still, it's a good idea to be cautious.
"In general, speak with your family physician if you are on medication to lower your blood sugar, and start with a small serving of blueberries to see if there is any reaction or side effect," Dr. McDonald says.
5. Allergic Reactions
Blueberry allergies are not common, but some people may be sensitive to a compound in blueberries called salicylates. Blueberries contain high amounts of salicylates — the active ingredient in aspirin that's also found naturally in many plants, Dr. McDonald says. Blueberry juice is especially high in salicylates.
This can cause side effects for people who have a salicylate sensitivity or intolerance, he says, including symptoms like:
- Gas and bloating
- Diarrhea or constipation
- Runny nose
In more severe cases, a person might experience hives or trouble breathing, which warrants immediate medical attention.
"This can be hard to diagnose because salicylates are not only in medication such as aspirin, but in many other foods as well," Dr. McDonald says. Plus, different people will present with different symptoms.
For many people who are mildly or moderately sensitive to salicylates, eating blueberries in smaller amounts can prevent uncomfortable symptoms, Dr. McDonald says.
If you have symptoms of anaphylaxis — a life-threatening allergic reaction marked by trouble breathing, a weak and rapid pulse and/or dizziness or fainting —call 911 or go to your nearest emergency room for medical help.
How Many Blueberries Is Too Many?
When eaten in moderation, blueberries can play an important role in a healthy, balanced diet. According to the USDA, adults should aim for 1 1/2 to 2 cups of fruit each day, and a serving size of blueberries (1 cup) can help you meet that recommendation.
For a visual aid, a cup of blueberries is about the size of a tennis ball. Eating more than that in a day isn't necessarily a bad thing unless it causes uncomfortable symptoms.
Consider adding blueberries to hot or cold breakfast cereals or blending them into a smoothie for a quick snack on-the-go. You can also toss blueberries into salads or pancake batter, bake them into desserts or add them to soups and side dishes.
Need inspiration? Try these eight blueberry breakfast recipes.
1. Can Eating a Lot of Blueberries Increase Your Risk for Kidney Stones?
According to Dr. McDonald, it depends on the type of kidney stone.
"Blueberries contain oxalate and may increase the risk of developing calcium-oxalate kidney stones, but this depends on several individual factors." he explains. "For those who have produced calcium oxalate kidney stones in the past, it may be best to limit blueberries and several other oxalate foods in their diet."
Dr. McDonald says it's important to keep in mind there are several different types of kidney stones. Dietary recommendations or medications to reduce the risk are different for each type of stone.
2. Are Blueberries a Natural Diuretic?
A diuretic is a type of medication that helps you move extra fluid and salt out of your body, according to the Cleveland Clinic. They are often prescribed to treat high blood pressure and manage other conditions.
There is limited research or evidence to support claims that blueberries work as a natural diuretic, per Dr. McDonald.
3. Can Eating Too Many Blueberries Make You Sick?
There's a reason we often hear the phrase "everything in moderation." Even though blueberries are a healthy food to include in your diet (as long as you're not allergic), it's possible to overdo it.
"Eating too much of anything can make you not feel well," Dr. McDonald says. "The most common side effect is bloating, gas and diarrhea due to the fiber content in blueberries."
- National Library of Medicine: "Vitamin K"
- National Library of Medicine: "Blueberry"
- Cleveland Clinic: "The Health Benefits of Blueberries"
- University of Michigan Health: "Warfarin and Vitamin K"
- Mayo Clinic: "Aspirin Allergy: What are the Symptoms?"
- Cleveland Clinic: "Diuretics"
- Mayo Clinic: "Chart of High-Fiber Foods"
- Mount Sinai: "Vitamin K"
- American Dental Association: "6 Tips for a Healthier Smile"
- Mayo Clinic: "Dietary Fiber: Essential for a Healthy Diet"
- National Institutes of Health: "Vitamin K"