Some Protein Bar Companies Are Lying to You

Hate to say it, but IMO fiber isn’t actually a fiber.


The replacement? Fiber. You may have noticed everyone is advertising “low net carb” protein bars, implying that the 10 to 15 grams of fiber aren’t actually digestible carbohydrates.

The problem? That isn’t exactly true. 

The fiber of choice for protein bar companies is something called isomalto-oligosaccharide (IMO) fiber. When IMO fiber was first being considered for use as a food additive, researchers subjected it to two enzyme tests to see whether either could break it down. The result: Neither enzyme broke IMO down, so voilà — it isn’t digestible, it’s a fiber!

Not so fast.

Several recent studies, including one by Jacob Wilson, Ph.D. (@themusclephd), did a thorough analysis of the way IMO breaks down in the body, and the results are startling.

Those early tests were technically correct — mouth and stomach enzymes DON’T break down IMO. That’s because the enzyme that breaks down IMO fiber isn’t in your mouth or your stomach. It’s in your small intestine.

Wilson ran a full battery of tests on the digestibility of IMO fiber — from blood-sugar response to breath hydrogen analysis. Similar to other recent studies, Wilson found that IMO does in fact get digested in the small intestine. If it were a true fiber, it wouldn’t. (It would get fermented in the colon.)

What does this mean? 

IMO is a good old-fashioned carbohydrate, NOT a fiber.

This is disturbing news. IMO is getting digested and metabolized, and all those carb calories aren’t showing up on the Nutrition Facts panel.

So if your diet calls for plenty of carbohydrates, IMO is great. But if your diet calls for low carbohydrates, then IMO bars are wolves in “low net carb” clothing.

If you (like many of us) are borderline religious about your macronutrient ratios, then this is a serious problem. By masquerading as “low net carb,” IMO protein bars are throwing your calculations way out of whack.

Let’s be real, fiber isn’t the sexiest of topics in the nutrition world, so most companies could probably be forgiven for not being totally up-to-date on the research.

Luckily, several companies have started to dump IMO in favor of other fiber sources; they’re doing their homework and following the science.

Look to see other fiber sources popping up in protein bars as more and more companies (and health-conscious consumers) discover the truth about IMO.

The lesson here is simple: Read the ingredients list. No matter what the Nutrition Facts panel claims, if you see IMO (or isomalto-oligosaccharide) as an ingredient, that bar isn’t low-carb.