The ‘prebiotic’ nature of prebiotic fibers depends on manufacturing conditions. Questions swirl around one category of these fibers, the IMOs (isomalto-oligosaccharides). IMOs occur in tiny amounts in nature, but the fibers on the market are made through a multistage enzymatic process with corn starch or tapioca starch as typical starting points. Essentially the starch molecules are first broken down into simpler sugars and then are reconstituted into longer chain molecules that can claim to act as dietary fiber that will resist digestion until reaching the colon.
The ingredient is usually supplied as a syrup that is easy to formulate with and has featured in a number of energy and nutrition bars. They can offer a fairly benign label claim; they are often referred to as ‘tapioca fiber’ or ‘corn fiber.’ The fibers are generally well tolerated, which can allow some manufacturers to make some spectacular fiber claims on labels. In one case a manufacturer of a nutrition bar that lists tapioca fiber on the ingredient deck claims 108% of the dietary fiber RDA in a single bar with a very low amount of sugar called out on the label.
But that digestibility and ease of use can be the rub, said food industry expert Tim Avila, principal in the Orange County, CA-based consulting firm Systems Bioscience. Concentrated slugs of fiber have usually been associated with gastric issues among some consumers not used to ingesting them. Dietitians in the past have often advised consumers to start slowly when adding larger doses of fiber to the diet to see how they cope with the typical gas and bloating issues. The idea in the past has been that it takes time for the microbiome to adjust to this new, hard-to-digest food source and to build up the appropriate suite of microbial species to reliably ferment these molecules without undue discomfort.
“In these manufactured fibers there could any amount of partially to fully indigestible fiber,” Avila told NutraIngredients-USA. “As digestiblity goes down you are going to have the gastrointestinal issues. As digestibility goes up you might tolerate it better but then you are going to have real problems with glucose.”
Some experts in the field have raised issues about how some of these IMO fibers perform. Jack Oswald, CEO of Isothrive, a company that markets a prebiotic ingredient that was researched and developed at Louisiana State University, said the building blocks of some of the fibers on the market that fly the IMO flag are not sufficiently strongly linked together to really resist digestion. The label might say fiber, but the body sees something else—a source of sugar.
“Some of these IMO ingredients just rapidly fall apart into a big bolus of glucose in the system,” he said.
IMO can mean a lot of things
A 2011 paper by three French researchers outline the boundaries of the issue. The definition of the term IMO has changed over the years they said.
“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,” they wrote. And more recently, ingredients with α-(1→3) linkages have been included in that bargain. The lower the number in that linkage designator, the more easily the molecule is broken down and digested. Leaving the digestibility of the base molecule aside, in some production processes there can be some simpler sugars still floating around in the tank which some producers then remove through a fermentation, filtration or other processing steps. The GI index of the final ingredient depends on the quality control at that juncture.
The paper lays out the many different ways these ingredients can be manufactured. One big advantage of selecting IMOs as a target point is the processes, though complicated-looking to the casual observer, are much simpler than those required for other functional fibers, so the cost is lower. But that multiplicity of manufacturing methods means that the final ingredients, though all technically IMOs, could behave quite differently depending on who made them and how.
“It thus brings a great disparity in the IMO structures and composition of final products and therefore the need for step-forward analytical methods. IMOs present the advantages of being produced from highly available and relatively low-cost plant material (hydrolyzed starch, saccharose, etc.) through a simple enzymatic process compared to other functional oligosaccharides extracted from plants. However, the use of hydrolyzed starch implies the presence of residual digestible low DP malto-oligosaccharides and the co-production of glucose which not only considerably lowers the global added value of the product but also its beneficial effect on the host,” the researchers wrote.
Possible blood sugar spikes
There have been some reports that some IMOs have caused blood glucose spikes among consumers, which could be a concern for diabetics who might consume a product expecting a low net carb load. In one case, an IMO was the subject of a class action lawsuit filed in 2013 against Quest Nutrition LLC that alleged the company was overstating the fiber content and understating the carbohydrate content of its nutrition bars. (Quest lists ‘corn fiber’ on its label.) That suit was subsequently dismissed.
So what’s the takeaway? It certainly is possible to produce an IMO that performs like the prebiotic fiber it claims to be on the label. “The prebiotic effect specificity has been proved to be driven by the nature and the structure of the oligosaccharides,” the French researchers wrote. But for a consumer, it’s difficult at the moment to know if the IMO used in a product has solid digestibility data behind it that could be linked to an ingredient brand, since generic ingredient callouts still seem to be the rule. And a key point hovering over the entire discussion is that the term ‘prebiotic’ is at present mostly a marketing term.
“The term prebiotic is not regulated by the FDA. The concept of prebiotics was introduced two decades ago. The original definition went through several revisions and the scientific community continues to debate what it means to be a ‘prebiotic’. Lacking a legal definition, the food and supplement industry, consumers and healthcare professionals add their own slants to this term. Advances in community-wide sequencing and glycomics reveal more complex interactions between putative prebiotic substrates and the gut microbiota than previously considered…and requires consensus among scientists before policy makers can come up with an appropriate definition of ‘prebiotic’. Until then, ‘prebiotic’ is a marketing term at best,” said Kantha Shelke, PhD, principal in the Chicago-based food consultancy Corvus Blue LLC.