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The Truth About Low-Carb Protein Bars

Finding healthy and macro-friendly food on the go is one of the biggest struggles for anyone trying to achieve body composition goals. 

You can be completely devoted to meal prep, but eventually life will get in the way.

You’ll find yourself in a sticky situation, weak from hunger, and so ravenous that you can barely think. You’ll be desperate for a snack that will stave off the hunger without making a dent in your progress.

Enter the ‘low carb protein bar’! 

Generally under 5g of net carbs, with over 20g of protein and just short of 200 calories, these bars sound too good to be true. Unfortunately, it turns out they probably are.

Low-carb, high-protein bars are the new fitness trend. There’s nothing more convenient than a wrapped bar that you can pop in your gym bag, purse, or car, and whip out in case of emergency (much easier than carrying a blender, ice, and bag of whey at all times).

While in the past energy and protein bars were jam packed with nuts and dried fruits, and have featured nutrition labels pathetic enough to make a flexible dieter cringe, we’re in the midst of a protein bar revolution.

More and more companies are coming out with what are seemingly ‘miracle’ protein bars.

They are super low carb, boast an impressive amount of protein, and are even delicious. With flavors like chocolate chip cookie dough that taste like you’re eating batter off a spoon, it’s hard to resist ditching “real food” altogether and subsisting off of these bars alone.

What are Net Carbs?

In order to understand how food companies are able to create delectable bars that are so low-carb, it’s necessary to distinguish between ‘total carbs’ and ‘net carbs’.

Once carbohydrates are consumed, they are converted to glucose to be used as fuel.

If you consume more carbs than needed, your body will store some of those carbs as glycogen in the muscles and liver. The rest, sadly, will be stored as fat.

But not all carbs are created equal. There are simple carbs like sugar or refined starches that are absorbed quickly and cause insulin to spike significantly.

There are also complex carbs, like whole grains and vegetables, which contain a lot of fibre and move through the digestive system slowly. These carbs have a smaller glycemic load.

Food manufacturers have come up with a new category of carbs for nutrition labels – ‘net carbs’.

Net carbs are total carbs minus the carbs that don’t have an impact on insulin levels and blood sugar, and aren’t fully digested, like fiber and sugar alcohols. For example:

Total carbs: 25g

Fiber: 5g

Sugar alcohol: 5g

Net carbs: 15g

But don’t worry; you’ll never have to do the calculation yourself. Food companies are more than happy to do the calculations for you.

Generally, you’ll find the net carbs sitting above the total carb line, because low-carb food items appeal to most consumers and food companies know it.

These new protein bars aren’t low in total carbs; they’re low in net carbs. And it’s the net carbs that diet junkies tend to focus on.

How do they achieve such low levels of net carbs? We have isomalto-oligosaccharides (IMO’s) to thank for that.

What are IMOs?

IMOs are the macro-friendly replacement for simple sugars, and the backbone of low-carb protein bars. They make bars chewy, sweet, and actually pleasant to eat (mitigating the dry chalkiness that comes from protein powder), and most importantly, low net-carb.

They are promoted as low GI, prebiotic fibre that isn’t digestible, but rather moves through the small intestine undigested to the colon, where it is fermented and contributes to our “good” bacteria.

IMOs are products of starch. Starches are polymers; they consist of many glucose molecules strung together by chemical bonds to form a long chain.

These glucose polymers are then broken down into shorter chains (oligosaccharides). One of the products of the starch break down is Isomalto-oligosaccharides.

The glucose molecules in IMOs are connected by strong bonds that are not easily broken down in the gut.

As such, it is claimed they pass through the intestines unscathed, which is why they don’t cause an insulin spike and don’t contribute much in the form of sugar or carbs.

IMOs naturally occur in some foods, including soy sauce, miso, and honey. However, the IMO syrup that you’ll find high on the ingredient list of any low-carb protein bar is not natural. It’s lab created using enzyme-catalyzed hydrolysis.

Scientists simply manipulate a process that is already occurring to ensure that the glucose molecule bonds in IMO syrup are difficult to break.

Long story short, IMOs are a dieter’s dream. The high fibre content means volume, which equals satiety. Prebiotic fibre means a healthy gut, and we all know that the gut is like the second brain and critical to our health. And eating carbs that aren’t digested and don’t really count literally couldn’t sound any more appealing. The only problem is IMOs may not really be as guilt-free as they’ve been made out to be…

Are the carbs really undigestible? 

We’ve been gobbling protein bars imagining that the carbs we’re eating are disintegrating into thin air, with no consequences. But it turns out that IMOs aren’t as un-digestible as we thought. While not all of the prebiotic fibre is digested, studies have shown that at least some of it is.

Initial studies of IMOs using a digestive modeling system led us to believe that IMOs would not break down in the small intestine and would reach the colon intact.

But later studies have proven otherwise. In a human study conducted in 1992, six fasted subjects consumed 25g of IMO syrup while fasted.

Their serum glucose levels went from 109 mg/dL prior to ingesting the IMO syrup to 136 mg/dL within 30 minutes of consuming it. Their serum insulin levels rose in parallel with their glucose levels.

Researchers concluded that IMOs are 83% as digestible as maltose (which is a fully digestible carb) under resting conditions, and 69% as digestible after exercise.

While some IMO does make it to the colon, the majority of IMOs are digested in the small intestine, absorbed, and metabolized. Our bodies are, in fact, able to break the strong IMO bonds, according to this research

The brush border of the intestinal lining is where the final digestion of carbohydrates takes place. This brush border contains an enzyme (sucrase-isomaltase) that is capable of breaking the “strong” bonds that are supposed to make IMOs indigestible (alpha-1,6-glucosidic bonds).

Unfortunately, if the bonds are broken down, we’re left with glucose molecules that are digested and will cause a spike in insulin. They are certainly not carb- or calorie-free. What does that mean? The nutrition labels are seemingly wrong.

Read our guide to managing blood sugar and improving insulin sensitivity for body composition


We’ve established that some, but not all, of IMOs are digested in the small intestine, while the rest pass on to the colon.

There, bacteria break down the IMOs, producing gas, and making us gassy and bloated.

If you think you’ve experienced bad bloating before, try chomping down a few low carb bars and see how you feel. It brings the term food baby to a whole new level.

You consume too much IMO syrup and, male or female, will feel like you need to shop in the maternity section. To avoid bloating and gas, keep your IMO consumption to a minimum.

Replacing real food with protein bars

While protein bars may not be as low-carb as we once thought, it doesn’t mean that they’re unhealthy, or that you should never eat one again. However, the convenience that these processed foods offer can pose a risk.

It’s very easy to slip into the habit of replacing real food with protein bars, even when it’s not necessary.

For most people, a chocolate brownie-flavored snack is more appealing than a plate of meat and vegetables. It feels like a treat – almost like cheating on your diet.

As you incorporate these snacks into your diet, you’ll find yourself more and more likely to opt for a pre-wrapped bar than fill up on healthy meats, vegetables or “real” foods that offer vitamins and minerals that processed foods simply can’t compete with.

While these protein bars aren’t “bad” for you in absolute terms, they’re not anywhere near as good for you as real food.


Sugar for so many people feels like a real addiction. Some of us have to cut it out of our lives completely in order to gain control over cravings (yes, I’m speaking from experience).

While the rare individual finds sweets unappealing, for many of us, just a taste of a sweet is enough to send us into an uncontrollable spiral of biscuits, cakes, candies… anything that will engender late that sugar-induced euphoria (and unfortunate subsequent crash).

The ‘addiction’ is natural. When we eat sweets, the neurotransmitter serotonin is released, and it makes us feel happy.

We begin to associate sweets with happiness, and we begin to crave them. Just like a former smoker shouldn’t take a drag, sugar addicts shouldn’t eat sweets. Even artificially sweetened or low-calorie goodies will open the floodgates.

And that relatively harmless protein bar can easily make staying on track with a diet unnecessarily difficult. There’s no need to make things harder for ourselves.

The Bottom Line on Low Carb Protein Bars

Protein bars made with IMO syrup won’t make you fat. Even with the caloric difference from the digested prebiotic fibre, we’re probably only looking at an additional 100 calories per bar.

Still, it’s best to keep your distance. While very helpful in a pinch, “diet foods” can become addicting.

At the end of the day, even if you’re eating something with an impressive amount of protein, hardly any fat, or low-carb enough to satisfy a keto aficionado, bear in mind what you’re replacing.

Processed food is processed food, and it will never be able to fill the shoes of real food.


Learn the secrets behind Ultimate Performance’s body transformations, nutrition principles and much more in our range of specialist books.  

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