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Secret Side Effects of Eating Protein Bars, According to Science

Take a look at the ingredients (and the science) before you unwrap one. 
FACT CHECKED BY Olivia Tarantino

It's 7 a.m. and you're starving. Only problem? There's no time to cook eggs because you're late for work. So, you grab a protein bar from the pantry or you swing by a convenience store for a coffee and one of the dozen or so protein bars on the rack. There's no shame in opting for a more grab-and-go option than a homemade one—those bars fill you up! They make you feel like an athlete. They taste pretty good. Even though you'd rather eat a doughnut, you feel better about eating a protein bar. Maybe you do that every day.

It seems like a good practice, after all, it is protein, right? Protein seems synonymous with good health these days, but that doesn't mean that all protein bars are healthy or can provide health benefits. Read on to learn the secret side effects of eating protein bars, according to science. And, if you're hungry, check out our review of 15 Best Healthy & Low-Sugar Protein Bars, According to Dietitians.

Eating protein bars may save your muscle.

fruit nut granola bar

As you age, you lose muscle mass and strength unless you do something about it. The technical term for this age-related muscle loss is sarcopenia. However, many studies have shown that increasing your protein consumption in addition to resistance training can help you preserve your muscle. One study in Nutrition in Clinical Practice suggests that protein supplements, like protein bars, are useful in preventing sarcopenia and that whey protein is best, increasing muscle protein synthesis more so than casein or soy proteins. Maintaining muscle as you age has many benefits, including higher metabolism and weight maintenance, better blood sugar control, increased activity, fall prevention, less inflammation, and better heart health.

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You could gain weight.

Refrigerated protein bar on a counter

Many protein bars are very high in calories, on par or even higher than some candy bars. MET-Rx Super Cookie Crunch, for example, weighs in at 410 calories and 14 grams of fat. That's the same amount of fat and 130 calories more than you get in a regular Snickers bar. If you're trying to gain weight, a protein bar makes sense because it's calorie-dense, but that'll work against you if you're trying to slim down.

It may make you hungrier.

eating a protein bar at a desk with a laptop

While many protein bars avoid added sugars, some contain the worst kind—high fructose corn syrup, a cheap sweetener that studies like one in the journal Frontiers in Nutrition which shows is more effective at causing obesity than regular sugar and actually increases appetite. Some of these nutrition bars are little more than candy bars in disguise. Nutra Grain Cereal Bars come in strawberry, raspberry and other fruit flavors, but contain little actual fruit but rather a puree made up of mostly fructose, sugar, corn syrup, modified food starch and wheat gluten. One bar contains 12 grams of added sugars, the same amount you get in a serving of Fruity Pebbles cereal.

You could develop metabolic disorders.

stack of protein bars

Eating too many foods high in added sugars can contribute to countless metabolic diseases that include obesity, type 2 diabetes, and heart disease, according to the Centers for Disease Control and Prevention. And some of the leading sources include sweet snacks like, cookies, cakes, pastries and protein bars. Again, don't get hoodwinked by the words "protein" on the package; check the Nutrition Facts box on the back.

Protein bars can be notorious for loading up on added sugars to make them more palatable. In fact, some bars may include upwards of 20 grams of sugar—that's about what you'd get by eating two Tootsie Roll Pop lollipops. "As a general rule, sugars in a healthy protein bar shouldn't exceed the grams of protein," says registered dietitian Trista Best, RD, with Balance One Supplements.

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Jeff Csatari
Jeff Csatari, a contributing writer for Eat This, Not That!, is responsible for editing Galvanized Media books and magazines and for advising journalism students through the Zinczenko New Media Center at Moravian University in Bethlehem, PA. Read more about Jeff