Earlier this year, the FDA released its industry guidance report on dietary fibers.

Isomalto-oligosaccharides (IMOs) weren’t on the list.

In fact, IMO manufacturer BioNeutra submitted a petition to the FDA to have IMOs added to the dietary fiber list — they were denied.

Based on our consideration of the scientific evidence and other information submitted with the petition, and other pertinent scientific evidence and information, we conclude that the strength of the evidence does not show that the consumption of IMO has a physiological effect that is beneficial to human health. Consequently, we do not plan to propose to amend the list of nondigestible carbohydrates that meet the definition of dietary fiber to include IMO as a dietary fiber based on this scientific evidence.

The FDA, denial response to BioNeutra.

Importantly, guidance documents are simply the FDA’s current thinking on a topic; they aren’t laws. While we can expect some companies to begin reformulating their products, not all will, and IMOs will remain a falsely labelled fiber for the foreseeable future (say that five times really fast).

Why this matters

IMOs entered into the spotlight with the launch of Quest Nutrition’s Questbars, a protein bar determined to be, as they say, candy in disguise. These things boasted 20 grams of high-quality protein and 15+ grams of fiber, making them every gym-nut’s dream come true.

As with any successful venture, competitors began to pop up with similar protein bar formulations, all using IMOs to get that fiber in (e.g., OhYeah’s One Bars).

Quest ended up in some lawsuits challenging the nutrition info of their Questbars, and ultimately ditched the IMOs in favor of soluble corn fiber, a prebiotic fiber that benefits glycemic control.

The copy-cat bars didn’t follow suit. Most high-fiber bars on the market still use IMOs.

Eat IMOs, get sugar

The central issue with IMOs is that they are not a single compound, but instead a group of related compounds.

Although in a strict sense, IMO means glucosyl saccharides with only α-(1→6) linkages, commercial IMO syrup is generally accepted as a mixture of glucosyl saccharides with both α-(1→6) linkages and α-(1→4) linkages. Moreover, this definition has been extended in these past years to glucooligosaccharides linked by α-(1→6) linkage and/or in a lower proportion α-(1→3) or α-(1→2) glucosidic linkages.

Goffin et al. Crit Rev Food Sci Nutr. 2011 May; 51(5): 394-409. (edited for clarity)

It would be silly to expect different compounds to act similarly within our digestive tract, and this silliness is illustrated in an analysis of seven commercial IMO food ingredients, reporting that some portion of the IMOs were digestible.

It appears that most manufacturers have adopted a loose definition that is neither based on an accurate quantitative analysis nor consequence of metabolic impact. This is significant because claims, such as “low glycemic,” “zero calorie,” and the like, are certainly false, and may pose a health hazard to certain populations (diabetic patients and epileptic patients on ketogenic diets, in particular) while misleading others (those on low carbohydrate diets).

Madsen et al. J Food Sci. 2017 Feb; 82(2): 401-408

This isn’t too surprising considering that the most common base for IMO creation is hydrolyzed corn and tapioca starches…

IMOs produced from hydrolyzed starch do not conform strictly to the non-digestibility criterion of potential prebiotics as they are partially digested by isomaltase in the human jejunum while the residual oligosaccharides are fermented by bacteria in the colon.

Goffin et al. Crit Rev Food Sci Nutr. 2011 May; 51(5): 394-409.

Don’t believe me?

We’ve known since at least 1992 that IMOs are mostly digested. Researchers out of Japan had a small group of healthy men consume 25 grams of IMOs after an overnight fast. Blood glucose and insulin levels peaked after 30 minutes, but breath hydrogen levels also increased, indicating some fermentation. The researchers estimated that IMOs contributed about 70–80% of the digestible energy we get from sugar.

Another study compared the fermentation potential of 10 and 20 grams of IMOs with FOS (fructo-oligosaccharide), a known fermentable fiber. Breath hydrogen with both IMO doses was minuscule, indicating that almost all of IMO ingested was digested by enzymes in the small intestine. Moreover, IMO did not cause any abdominal symptoms, while FOS gave people distended stomachs and bad gas.

Most recently, IMOs were tested against dextrose (glucose) in a randomized crossover trial of healthy men and women. The image below shows, quite clearly, that there were no differences between the two for blood glucose, insulin, or breath hydrogen responses after consuming 50 grams of each.

Summing up

In short, read the ingredient label of your favorite high-fiber protein bar. If it uses isomalto-oligosaccharides (IMOs), then it is best avoided. The FDA has ruled that IMOs have insufficient evidence to be claimed as a dietary fiber, and a handful of studies suggest that they are absorbed with similar efficiency as sugar.