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Are Quest Bars Bad For You?



Short answer

Quest Bars can be hard on your gut. They also contain sucralose, which is a somewhat controversial sweetener that's probably safe in moderate amounts.



Recommended Alternative

Long answer

Quest Bars boast 17 grams of fiber. That's quite a bit. Most of that fiber comes from isomalto-oligosaccharides, or IMOs. These syrupy fibers are a natural product produced by yeast. They're hard for our bodies to digest, so they largely pass through our gut as fiber. Some of the IMOs in Quest Bars might be partially broken down in the gut - there's a chance you'll get a few extra calories. Quest has been sued before for allegedly overstating fiber content and understating total carbohydrates.

IMOs are a cheap source of fiber that's easy to produce. Fiber's not just important to keep things regular, however - it also provides food for the populations of bacteria that live in our gut. Different bacterial populations eat different kinds of fiber. The bacteria who eat IMOs make up a pretty small slice of the pie. If you're getting too much of your fiber from IMOs, other bacterial populations might decline and the balance of your digestive system may be thrown off.

It's not just IMOs, however. Quest Bars are high in protein - enough to kick the kidneys into overdrive and deprive your gut of the water it needs to function.  They've got milk protein, which the lactose intolerant can't break down, and whey protein, which infamously causes bloating and gas. They've also got a healthy dose of calcium, which can also cause digestive distress in large amounts.

All of these ingredients together may be the perfect storm for a sensitive gut. You might feel bloated and become constipated, or experience the opposite - runny stools and diarrhea. People who struggle with IBS, Crone's Disease or other gastro problems may be at higher risk of Quest Bar-consumption-related issues. Remember to diversify your sources of fiber and talk to your doctor if you think that Quest Bar are causing problems with your stomach or your bowels.

Quest Bars are sweetened with sucralose, which tastes like sugar but passes through your system mostly undigested. Sucralose is controversial: consumer advocacy groups like the Center for Science in the Public Interest claim that there's good evidence that it's carcinogenic and might interfere with fetal development. The studies on which they base that claim - one from Duke, another from an Italian scientist at the Ramazzini institute - have been criticized as sloppy and poorly executed in their peer reviews and the national media. So far, regulatory agencies in the US, Europe and elsewhere maintain that sucralose is safe and non-carcinogenic, however, it may still be best to err on the side of caution. 

Possible short-term side effects

  • nausea
  • bloating
  • constipation
  • loose stool
  • diarrhea
  • gut bacteria imbalance

Possible long-term side effects

  • cancer (insufficient evidence)

Ingredients to be aware of

  • sucralose
  • lactose
  • fiber (mostly in the form of imos)


  • good source of:
  • calcium
  • protein
  • fiber

Our Wellness Pick (what is this?)

RXBAR Protein Bars

  • High protein snack
  • Chocolate Sea Salt flavor
  • Convenient 12-pack box
  • No added sugar
Learn More!

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View Sources | Written by Sean McNulty
Published on: 11-17-2016
Last updated: 12-01-2023

Thank you for your feedback!

View Sources
Written by Sean McNulty
Published on: 11-17-2016
Last updated: 12-01-2023

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