Spuds are duds—and other not-so-healthy fruits and veggies

By John Murphy, MDLinx
Published February 28, 2019

Key Takeaways

It's better to eat any fruit or vegetable than, say, a plate of chicken wings or a bag of Fritos. That said, when you do eat fruits and veggies, be aware what's in them—some have better nutrients than others. For instance, frequently eating potatoes can potentially lead to weight gain (and not just chips or French fries, but plain old 'taters). And some fruits are loaded with more sugar than you might suspect. So, here are several fruits and vegetables that you might want to consider eating less often (although they're still better to eat than, say, a microwave burrito or a pack of M&M'S).


Bananas are a tasty and convenient snack—they even come in their own easy-to-peel wrapper. They're also rich in fiber and nutrients like potassium, vitamin B6, and vitamin C. Bananas are low in fats and protein, and only contain about 105 calories. But because more than 90% of these calories come from carbohydrates, people looking to reduce sugars may want to think twice about eating bananas on a daily basis.

But, consider this: Although unripe green bananas contain the same amount of carbs, most of these are in the form of resistant starch, not sugar. (Resistant starch is considered a fermentable fiber that helps lower blood sugar, reduce appetite, and improve gut health.) As bananas ripen from green to yellow, these starches convert to sugars.

On the glycemic index—a scale that measures how quickly a food causes blood sugar to rise—a green banana scores a low 30, while a ripe yellow banana has a medium value at about 50 to 60. (A can of Coca-Cola, for comparison, has a glycemic index value of 68.)

Bottom line: Bananas are fine on occasion, but consider unripe or less ripe bananas if you're watching your sugar intake.


It's hard to imagine a summer barbecue (or Thanksgiving dinner, for that matter) without fresh, sweet corn on the cob. But even the name—sweet corn—indicates this vegetable contains a good deal of sugar. (Wait—is corn a vegetable? Or is it a grain, or a fruit? Turns out, corn is all three.)

A typical 80-g serving of sweet corn contains about 16 g of carbohydrates with a middle-range glycemic index score of about 48. In a 2015 study on fruit and vegetable consumption, researchers at the Harvard School of Public Health found that people who regularly ate vegetables with a higher glycemic load, such as corn, tended to gain weight over time as compared to people who regularly ate veggies with a lower glycemic load, such as broccoli and Brussels sprouts. These people tended to lose weight over time. Still, corn isn't all bad—it's a good source of dietary fiber, vitamin C, pantothenic acid, and manganese, as well as lutein and zeaxanthin, two carotenoid antioxidants that are healthy for your eyes.

Bottom line: Enjoy corn at barbecues and on holidays—but go easy on the added butter and salt.


Like sweet corn, it's difficult to picture a summertime event without a big, cool, sweet slice of watermelon. But is watermelon any good for your health? True, watermelon contains—you guessed it—water. In fact, nearly 92% of watermelon is H20.

But this sweet summer treat also has a high glycemic index of 72—the same number as a slice of plain white bread. However, watermelon has less than half the glycemic load than a slice of bread. (A quick word of explanation: Glycemic index and glycemic load aren't the same thing. While the glycemic index is a measurement of how quickly a food raises blood glucose, the glycemic load also takes into account the amount of carbohydrates in a serving of food.) So, even though watermelon has a high glycemic index, it has a glycemic load of around 4, compared with the glycemic load of 10 for that slice of bread.

Still, does that make watermelon good for you? Not especially, although it does contain a healthy dose of vitamin C as well as proportionately more heart-healthy lycopene than a raw tomato.

Bottom line: A refreshing slice of watermelon won't cause a sugar crash, but it won't juice you up with nutrients either.


Once a rare tropical treat in supermarkets, mangoes are now more available than ever. As a common component for sweetening smoothies, sushi rolls, and guacamole, mangoes may be on your plate or in your cup without you even knowing it.

If that's the case, you might want to take a second look at your mango intake. For instance, one mango is loaded with 30 g of carbohydrates and about 26 g of sugar. It also scores a middle-to-high value of 60 on the glycemic index, along with a glycemic load of 9. And as a mango ripens, its glycemic index rises. On the upside, mangos are a good source of certain vitamins, minerals, and antioxidants. In fact, one mango will supply you with your entire daily requirement of vitamin C. Mangoes are also high in vitamin A, folate, and potassium.

Bottom line: Eat mango fruit in smaller portions, and watch out for mango included in your smoothie or guacamole.


Potatoes, like corn, are a starchy vegetable that the Harvard School of Public Health researchers found to be linked to weight gain. (Perhaps surprisingly, peas are yet another not-so-healthy veggie, the researchers reported.) With this kind of notoriety, the potato has received a lot of bad publicity lately, even described as "probably the most cautioned of all veggies."

But potatoes are not all bad. A medium-sized (6 oz) white baked potato—with the skin—has 159 calories, 36 g of carbohydrates, and about 4 g of fiber. Potatoes (again, with the skin) are also loaded with potassium, magnesium, and vitamins B6 and C.

Interestingly, the type of potato, the way it's grown, and the way it's prepared can affect its glycemic index. A medium baked potato may have a glycemic index of 85, while a boiled potato may score a 50. Like bananas, potatoes have resistant starch. This starch breaks down when potatoes are cooked, but then it resets when the potatoes get cold—which explains why the glycemic index of cold cooked potatoes is lower than that of hot cooked potatoes.

In any case, the worst thing about potatoes is not the potatoes themselves, but the butter, salt, and deep-fry oil that we add to them.

Bottom line: Eat your cooked potatoes cold (as in potato salad), and skip the sour cream, butter, and bacon bits.

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