T Nation

carb question

Is it true that you can subtract fiber from a carb count? For example alot of protein bars say 2 net carbs but actually have 20 carbs. Any insight on this would be great, thank you.

Yes. Because Fiber doesn’t get fully digested and it passes straight through you.

Some say some of the fibre you take in is actually digested but most of it passes right through you. Hence it being “ruffage”.

Yes, you can subtract fiber from carb counts. Although fiber (cellulose) is technically a carb, it is not digested by the human GI tract. It serves more of a purpose of adding bulk to the stool and moving things along.

In the case of protein bars, however, you aren’t going to have 18 of those 20 grams coming from fiber. Most of those carbs come from sugar alcohols, which is now being classified as a carbohydrate. Sugar alcohols, such as glycerine, are good for between 4 and 4.5 calories per gram, but they don’t cause as much of an insulin spike as straight sugar. That is the reasoning behind calling them “impact carbs.”

I don’t completely buy into the hype of impact vs. non-impact carbs. It is true that you can take advantage of the type of carb and the timing of carb intake to manipulate insulin release, but a calorie is still a calorie. Check out the Atkins book for a good explanation of carbs/insulin info.


Who should answer this one, me or Terry? LOL

Well in regards to the protein bar example you gave… the 18 grams of “missing” carbs isn’t all fiber. Most of it is sugar alcohol, or polydextrose, or maltitol, or some other crap like that. Supposedly doesn’t cause a blood sugar response therefor it isnt included in the “net carbs” but still has a calorie value thus being included in the total carbohydrate count. I’ve heard things about glycerol being able to be metabolized into blood sugar despite reports that say otherwise, so maybe someone else will chime in with more specifics.

Blarg, sorry for repeating what has already been said more effectively.

Thunder you’ve got your hand problems, either let Terry do it…or copy and paste from the previous post of yours regarding fiber and physiology and all that jazz.

Fiber consists of both fementable and non-fermentable (unavailable) carbohydrates and fermentable forms have been found to contain 2kcals/g in humans(anywhere between 1.5 and 2.5 actually)and non-fermentable forms have been found to contain 0kcal/g. Since dietary fiber contains both forms, the established figure is 1.5kcal/g of dietary fiber.

As as been said before fiber can be anaerobically fermented by the colonic microflora to short chain fatty acids (in addition to CO2, H2, etc). Because it’s an anaerobic process, less energy is recovered from fermentable fiber than 4kcal/g. Foods that contain large amounts of hemicellulose and pectins such as fruits and vegetables are more fermentable than foods high in cellulose.

Do I count fiber? Nope. I can’t be bothered. It’s probably just as eas4y to subtract it all. Or you could subtract half of it which is technically more correct.

I just copied my previous post. LOL

No way I was retyping that.

Hah, damn straight, especially not with that hand.

Man I love reading that post.


its as nutrition as eating cardboard witht the staples still in it.


Great repost

I have been wonder about this issue for a while. I subtract fiber from my total carb count, but dont take the time to screw with the calorie totals.

Do you take the time to subtract from the kcal total also?


I’m just wondering because I’m eating, as we speak, a tri-o-plex(damn good) which lists at 34g carbs but only has 9 impact carbs becasue of “fiber, glycerin, oats, oat flour”.

Trioplex bars were tested and came back with lower protien, higher fat, and much higher carb count than listed on the package. Check the link.

You know what? I literally don’t even think about fiber. I don’t even subtract it. I just work off the total carb count. You can really only worry about so much, and unless you’re consuming tons of fiber, I don’t feel it will add up to much difference.

Having said that, maybe I’ll start subtracting some fiber grams … or half of them anyway.

For some reason my endocrinologist said you can subtract the fiber, but not until there is a minimum of 5 grams of fiber. So, for example, if there are 3 grams of fiber, you count them as 3 grams of carbs, but if there are 6 grams of fiber you can count them as zero carbs.

I have no idea of where he came up with that, but that’s what they tell their diabetic patients. I like Thunder’s explanation better.

roc, lots of good input, here, and different points of view.

The bottom line is that if you’re eating very few carbs, you could make persuasive argument for subtracting fiber from total carbs. And if you’re bulking or not on a carb-restricted diet, you could make persuasive argument for NOT subtracting fiber from total carbs.

Either way you choose to go, if you’re keeping a food log, you’ll be making adjustments to your program along the way so that you continue to progress towards your goals.

Thanks everyone, I was just wondering what everyone thoughts were on the subject. I never go by carb advantage labels, probably why I never eat protein bars, because of the misleading labels, in my mind anyway.

Yes, the food log does make things much easier after a while.