They’re creamy, cool and delicious — but are fruit smoothies a hidden health hazard?

Some dieticians have gone so far as to describe them as downright dangerous.

There’s just too much sugar in store-bought smoothies, according to Andy Bellatti, MS, RD, a Las Vegas-based dietitian. These smoothies, which usually use fruit juice as a base, get a bad rap among nutritionists for being high in sugar and because many have little fiber or protein relative to the calories they pack, he says.

“When you make smoothies at home, you can make them very nutritious," says Bellatti. “But many commercial smoothies are made with so much fruit juice that they become liquid candy bars.”

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Trying to lose weight? Lose the typical store-bought smoothie. “People forget that if you are watching calories, fruit juice is pretty much empty calories,” says Bellatti. “They have a bit of nutrition, but it doesn’t make up for the amount of sugar they contain.”

The large-size Mega Mango Smoothie at one popular juice/smoothie chain contains a whopping 89 grams of sugar.

Too much fruit juice may also boost the risk of type 2 diabetes. A 2010 study published in the American Journal of Epidemiology found that out of roughly 44 thousand adults in Singapore, adults who consumed two servings of fruit juice per week had a 29 percent higher chance of developing type 2 diabetes.

Whole fruit is a much better bet. A 2013 review in BMJ found that three large studies on fruits and type 2 diabetes arrived at a similar conclusion: “Greater consumption of specific whole fruits, particularly blueberries, grapes, and apples, is significantly associated with a lower risk of type 2 diabetes, whereas greater consumption of fruit juice is associated with a higher risk,” wrote the paper authors.

But some smoothie joints use frozen apple purees and others that don’t include the peel. “Commercial smoothies often also used pureed fruit, removing one of the most valuable parts of the smoothie: the fiber from the fruit,” says Bellatti.

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Making a healthier smoothie

To enjoy a healthier treat — and save money at the same time — make your smoothies at home using these tips.

Include veggies. Adding dark greens such as kale to fruit smoothies is a good idea, although Bellatti says many people prefer spinach because the taste doesn’t “show through” as much.

Vary the ingredients rather than making the same smoothie each day.

Get nutty. Bellatti suggests grinding almonds, chia or pumpkin seeds into your smoothie. “Oat or wheat bran is another great fiber addition — the oats also help control bad cholesterol,” he says.

Make it thick. Bellatti finds that smoothies provide longer-lasting fullness if banana or mango slices are frozen and added for thickness. “People use ice, but it just waters the smoothie down,” he says.

Experiment with add-ins. Popular options Bellatti and other nutritionists like include coconut water, cinnamon, cacao nibs, nori (a type of seaweed), wheat germ, nutritional yeast and hemp seeds.

Tailor the smoothie to your needs. If your blood pressure is creeping up, try adding more bananas or blueberries. If you’re looking to lower your risk of Alzheimer’s disease, you might add blueberries, curcumin or unsweetened cocoa powder.

Among Bellatti’s favorite smoothies are the “Superfood Shamrock Shake” (created by a Chicago nutritionist), “no-recipe-needed” smoothies from the website Serious Eats and “54 Health Smoothies for Any Occasion” from greatist.com.

Or check out this blueberry smoothie recipe created by diabetes specialist Daniel Nadeau, MD.

Related: Four Foods That Could Lower Your Blood Pressure

Kathryn Olney is a freelance writer and editor who has served as a reporter and editor for California, San Francisco and Mother Jones magazines.