What Kind Of "Fiber" Is in Your Protein Bar?
What Kind Of "Fiber" Is in Your Protein Bar?

Protein bars are awesome. They’re tasty, affordable, quick, convenient, and provide the perfect snack you need any time of day. Protein bars deliver a solid dose of muscle-building protein, but many also claim to be high in dietary fiber.

Delicious though they may be, have you have really stopped to think about what’s really in your favorite protein bar? Sure, there’s some combination of whey, casein, egg, or even soy protein, but what about all of the “other” ingredients. More specifically, what kind of fiber is in all of those bars that tout a high fiber content?

Related - Top 10 Best-Selling Protein Bars

This guide is here to answer all the fibrous questions percolating in your brain and provide some other informational nuggets you can tuck away for a rainy day. It’s time to go down the hole with fiber!

Types of Fiber

Before we get into the different forms of fiber that you’ll commonly encounter in your favorite protein bars, let’s first take a second to discuss what fiber is. In its most basic sense, fiber is the indigestible portion of food derived from plants. In other words, it’s the part of that plant this isn’t broken down by the body. Does that mean it’s totally useless for our bodies? Not in the least, fiber serves several important roles in the human body, which we’ll get to in a bit.

Now, there are two types of dietary fiber in the body -- soluble fiber and insoluble fiber. Soluble fiber dissolves in water in the guy and forms a gel-like substance which helps to blend with water in the gut, forming a gel-like substance, which slows digestion. Common sources of soluble fiber include oats, beans, lentils, barley, and some fruits & vegetables, such as apples or carrots. Benefits of soluble fiber include regulating blood sugar levels and various other metabolic benefits. [1]

On the other hand, insoluble fiber does not dissolve in water and passes through the digestive system mostly intact. It functions primarily as a "bulking" agent, and may potentially speed the passage of food and waste through your GI system. [2] Insoluble fiber is mostly found in the outer bran layer of grains, vegetables, and wheat bran.

Prebiotic vs Probiotic

Anytime fiber or the gut is brought up, you’ll no doubt here talk of prebiotics and probiotics. These sounds like important words, after all, they used in advertising campaigns all the time, especially when discussing yogurt. But, what are they exactly?

Probiotics are live bacteria present in yogurt, pills, and various other fermented foods, including kefir, sauerkraut, and kimchi, that are beneficial to the digestive system and support immune function. [3] Individuals are often prescribed probiotic supplements by their doctor while taking antibiotics in order to resist some of the gut bacteria depleting qualities of antibiotics.

FYI, antibiotics kill all types of bacteria in the body, they don’t discriminate between the good type of bacteria in the gut and the “bad” kind causing an infection. That being said, probiotics are extremely sensitive to heat, processing and even the digestive system, which is why it’s hard to come by a high-quality probiotic supplement that actually contains live cultures. Another way to enhance good gut bacteria is by consuming prebiotics.

Prebiotics are a type of plant fiber that feeds the good bacteria in your gut. In other words, prebiotics are the “fertilizer” for the good bacteria that are already present in your gut. They help grow and sustain the good bacteria in your gut, which supports gut health, brain function, and overall well being. [4] Additionally, prebiotics are more resilient to heat, processing, and digestion than probiotics, making them ideal for use in supplement form.

Note: Virtually all of the fiber you’ll get from protein bars are prebiotics.

Benefits of Fiber

Fiber lends a number of important benefits in the human body. Here’s a list of the benefits, beginning with the most obvious and well-known benefit:

Keeps you regular

Consuming fiber boosts the size, weight, and “softness” of your stool. Bulkier stool is easier to pass through the body, lessening your chance of constipation. If you notice loose or watery stools, fiber can help to solidify the stool since it adds bulk.

Supports bowel health

High fiber intake can reduce your risk of hemorrhoids and diverticular disease, small pouches that develop in the colon.

Regulates blood sugar levels

Fiber slows the digestion of food, including sugar, which improves blood sugar levels. This is particularly important for individuals with Type 2 Diabetes or those classified as pre-diabetic.

Supports cardiovascular health

Soluble fiber present in oats, legumes, and various fruits and veggies have been shown to lower total blood cholesterol by reducing LDL (“bad”) cholesterol.[5] Additional research has found that consuming a high-fiber diet also lowers blood pressure and combats inflammation. [6][7]

Aids body composition

High fiber foods are more filling than foods with little to no fiber. Consuming high fiber foods can prevent overeating, thereby preventing unnecessary fat gain and supporting a lean, muscular physique. [8]

Fiber Recommendations

The recommended daily intake for fiber is 14g per 1,000 calories consumed. For the typical adult, this means that women should aim to consume about 25g fiber/day and men should consume approximately 35-38g/day. Unfortunately, given the standard western diet of hyper-processed, nutritionally void food that most adults consume they fall far short of this goal, often times only consuming 13-18 grams of fiber each day.

Eat a Variety

When it comes to getting your fiber in each day, it’s important to get your fiber from a variety of sources. The reason for this is that different fibers are found in different plants, and while each fiber offers a number of benefits, no single fiber can produce every possible health benefit attributed to fiber. This is why you can just get all of your fiber from a single over-the-counter supplement, such as Metamucil or Benefiber.

Fibrous Concerns

In today’s age, the thinking is, if a little of something is good, a lot of something is that much better. That’s not really true with fiber. Consuming too much can lead to excess gas, bloating, GI upset, diarrhea, constipation, or dehydration.

Additionally, if you’ve been living a low-fiber lifestyle as of late and want to start eating more fiber, do so slowly. Space out your fiber intake throughout the day, lest you suffer the GI symptoms described above.

Finally, when upping your fiber intake, make sure to increase your water intake as well. Remember, fiber absorbs and dissolves in water. To support this increased need for water, it’s imperative that you increase your water intake.

Now that fiber has been addressed, it’s time to move onto the various kinds of fiber you’ll find in your protein bar!

Common Protein Bar Fibers

Isomalto-oligosaccharides (IMOs)

Far and away, the most common type of fiber you’re likely to encounter in protein bars is Isomalto-oligosaccharides, IMOs for short. It’s also found under that trademarked name of VitaFiber™, and came to popularity when Quest bars debuted on the market several years ago.

IMOs are a moderately sweet carbohydrate that are roughly 50-60% as sweet as sucrose and contain a relatively high amount of prebiotic fiber. What this means is that IMOs contain fewer net carbs than common sweeteners like sugar, honey, molasses, etc. Plus, it has a low viscosity and helps retain water, which makes it ideal for use in a protein bar.

IMOs aren’t just a single type of sugar, or hydrolyzed starch. In fact, there are numerous IMOs, including: [10]

  • Cyclic IMOs
  • Gluco-oligosaccharides (branched IMO)
  • Isomaltulose
  • Koji-oligosaccharides
  • Nigero-oligosaccharides

Fiber Claims

When isomalto-oligosaccharides first broke on the scene, they were billed as a low-calorie sweetener touting a high fiber content. Companies from all over began using IMOs in their bars, based on some early research, conducted in vitro, demonstrating that isomalto-oligosaccharides may be high in fiber since it wasn’t digested in the small intestine, reaching the colon intact. [10] As a result, isomalto-oligosaccharides were added to protein bars in amounts exceeding 15g, giving the protein bar its “high fiber” content.

However, a number of subsequent studies in humans showed conflicting results on whether or not IMOs did, in fact, confer any prebiotic activity. [11][12][13] This may be due to the fact that isomalto-oligosaccharides, in fact, aren’t as rich in indigestible matter as was initially thought.

A handful of studies conducted in rats and humans have shown that isomalto-oligosaccharides are indeed digested in some capacity in the body. [14][15][16] On top of that, two other human studies offered proof that IMOs are digestible, with one, in particular, showing isomalto-oligosaccharides offer 75% of the energy yield of maltose, a disaccharide composed of two glucose molecules. [17][18]

This may be due to the fact that the various isomalto-oligosaccharides that could be contained in your bar are digested and absorbed at different rates, meaning they’re not as “calorie free” as advertised. [17][18][19]

The point of all of this IMO breakdown is that the “fiber” content of your protein bar may not be as high as you think it is, which means the “net carbohydrate” content is higher as is the total calorie content of the bar.

Finally, one other drawback to large amounts of IMOs in your protein bar is that it gives the bar a very tacky, gummy texture in your mouth, meaning it takes forever to chew and get stuck in your teeth. Additionally, the longer a bar with IMO sits on the shelf, the more it seems to harden up, making it that much more labor-intensive to chew.

Inulin (Chicory Root Fiber)

The second most popular type of fiber you’ll encounter in foods is inulin, a.ka. Fructo-oligosaccharide (FOS) inulin. Commercial inulin is extracted from a wide variety of foods including chicory, onion, garlic, agave and Jerusalem artichoke.

It’s easy to work with and has essentially no discernible taste or texture, making it ideal for use in packaged foods. It has a soluble fiber content of approximately 90-92 grams per 100 grams. In other words, 90% of inulin is fiber.

A few other ways you’ll see inulin described on ingredients lists include:

  • Chicory root extract
  • Oligofructose
  • Oligosaccharide

Inulin is used in everything from high fiber breakfast bars (Fiber One Chewy Bar) to ice creams, and even beverages. While you might think that inulin and isomalto-oligosaccharides are similar due to the word “oligosaccharide” present in both names, they’re actually a bit different. In fact, inulin represents an entire family of complex carbohydrates present in plants, ranging in size from a dozen units of fructose to several thousand. [9]

Research has noted the energy content of inulin is only 40–50% that of a digestible carbohydrate, yielding about 1.5 to 2.0 kcal/g. It’s practically indigestible in the small intestine and is fermented in the colon, where it feeds the good gut bacteria. [21] Another added benefit is that inulin consumption enhances the bioavailability of calcium. [21]

However, all is not as rosy as it would seem with inulin, particularly in regards to how its tolerated in humans when added in supplemental form (i.e. the form you get in protein bars). One study, in particular, showed that even as little as 5g/day of “sweet” inulin (short-chain oligofructose) led to significantly more GI distress (bloating, flatulence, cramping, diarrhea, constipation) than a 10g/day serving of “native inulin”. [20]

But, another study comparing inulin to cellulose (another type of fiber) found that inulin led to greater weight loss and a reduction in liver fat compared to the group receiving cellulose. [22] Note that the inulin group was receiving upwards of 30g/day of inulin!

The takeaway here is that depending on what kind of inulin is used in your protein bar, and how much of it you consume, will determine how much it affects your GI system. But, unlike IMOs, inulin is indeed a truer “fiber” in regards to its indigestibility.

While inulin is tasteless and textureless in protein bars, the fact that even moderate amounts of it can lead to severe GI distress in a large number of people make this less than an ideal fiber to include in great amounts in your protein bar.

Soluble Corn Fiber

Finally, we have one of the most recent fibers to enter the protein bar market in soluble corn fiber. As you would expect, it’s derived from corn, produced via enzymatic hydrolysis of corn starch. Though it’s newer to use in protein bars, soluble corn fiber has actually been used in the United States since 2007 in numerous foods and beverages. It’s also used abroad in Europe and Southeast Asia.

Soluble corn fiber is water soluble, very stable to heat, pH, and all the various processing “stresses” that occur in the manufacturing process, making it an ideal fiber for baked and unbaked protein bars. It’s low sugar, high fiber (~90% fiber) content make it ideal for reducing the sugar content of processed foods, while providing a good source of prebiotic fiber. Similar to inulin, soluble corn fiber resists digestion in the small intestine and is fermented in the large intestine.

Compared to both isomalto-oligosaccharides and inulin, it appears that soluble corn fiber is the most well tolerated by individuals at a variety of doses, with some research showing that consuming as much as 65g of it per day and 40g is a single dose is well tolerated.[23,24,25] There’s also a number of benefits that have been noted with consumption of soluble corn fiber including:

  • Enhanced calcium absorption [26]
  • Increased fecal weight [27]
  • Reduced post-prandial glucose and insulin response [28]
  • Prebiotic effect (increase in good gut bacteria) [27][29]
  • Increased satiety

The benefit to using soluble corn fiber over other types of fiber is that it’s well tolerated by most people, even in large doses, and helps bars to stay fresher longer as well as stand up to baking better than other fibers and sweeteners commonly used. The downfall is, outside of Quest bars, there aren’t a whole lot of other places you’re likely to find soluble corn fiber, probably due to cost.


Fiber is an essential component of every human’s diet, without it, things just don’t work properly, there’s no other way to say it. Gut bacteria can’t thrive, GI function suffers, blood sugar levels and appetite are more unwieldy, the list goes on.

Protein bars represent one way you can up your fiber intake, but as we showed above, some of these fibers aren’t all they’re cracked up to be. From fraudulent fibers to excess GI upset, “fake” filler fibers in bars are “ok” but shouldn’t be the main source of fiber in your diet. To satisfy your fiber needs, focus on a variety of whole foods so you get all the various types of fiber and the wealth of benefits they offer.

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