Some Fiber is Absorbed As Glucose? Westman v Rosedale


I am trying to find out whether fiber turns into glucose in the body as Dr. Westman states or whether fiber has no effect on blood glucose as Dr. Rosedale states.

My partner was reading Keto Clarity and showed me this rather strange paragraph: DOCTOR’S NOTE FROM DR. ERIC WESTMAN:

“There is often confusion between counting “net carbs” and “total carbs.” “Net carbs,” determined by subtracting the fiber grams from the total grams of carbs, works well for those who are not very rnetabolically sick or who don’t have much weight to lose. But because some of the fiber is absorbed as glucose and your goal now is to become ketogenic, the more prudent approach is to not subtract even the fiber grams from the total grams of carbs.”

This flies in the face of my understanding, said in The Rosedale Diet book by DR. RON ROSEDALE:

“A more useful classification of carbohydrates is as either fiber or nonfiber carbohydrates. High fiber carbohydrates are found mostly in vegetables and nuts. The major advantage of fiber is that it can’t be broken down into sugar, which means that it doesn’t raise blood sugar levels or send your insulin and leptin levels soaring. In fact, only bacteria (including some that inhabit our gut) can digest fiber at all, and they di- gest a type of fiber called soluble fiber into good fats that are used for energy by the cells that line our intestines.”

Can anyone shed some light on this apparent disagreement? I’d really love to know all the possible metabolic pathways for fiber.


I just want to add that according to this article Jimmy Moore (author of Keto Clarity), had a fibre intake too low and it was causing issues in his metabolism and test results. Not sure if it’s related to Westman’s statements.

Also in that same article is how some low-carb high fiber snacks actually raise glucose levels (mechanism of action isn’t defined though).

(Ketopia Court Jester) #3

Yeah, I’d like to know about this, too. As a profoundly deranged…er, metabolically deranged…individual, it would explain why I intuitively veer away from a lot of things otherwise considered low net carb.



(Todd Allen) #5

I’m inclined to believe Dr. Westman is right, but I don’t agree with him… More specifically he is probably right that some fiber can be absorbed as glucose but I don’t believe individuals should automatically count fiber as carbohydrate for the sake of prudence when the odds are high the amount of fiber absorbed as glucose is low. People should monitor blood glucose and ketones and see what their response is to the foods they eat.

(Jamie Hayes) #6

Great question well articulated.


The more processing, the greater the breakdown and digestability of the food product, including fibre. If you eat the food in its natural state, ok, subtract the fibre for calculating net carbs. But, not for processed foods. Big difference between digesting flax seeds versus ground flaxseed flour. Or whole fruit versus fruit liquified in a blender.


Agreed, this ties into the Green Vegetable Juice thread. The more processing, even something as simple as a blender, can adulterate the fiber in such a way as to make it something to avoid.


Does this actually justify the statement “some of the fiber is absorbed as glucose” that Westman made? It’s a pretty clear statement about glucose.


Thanks for this. This may be an argument for not eating fiber but not for the reasons Westman stated, which was because it’s absorbed as glucose.

Also the speculation about correlation between blending and juicing in that thread seems a little suspect.


I can speak for myself. I’ve seen it affect me as if I ingested starch or sugar.


I don’t doubt the effect you’re experiencing. Would it be right to call it glucose absorption from fiber?

Or is it your deranged metabolism responding by creating glucose (presumably from protein), in the same way that some people respond to artificial sweeteners, also with gluconeogenesis?

In my experience a great many things can trigger gluconeogenesis so it’s poor science to just guess at it. I have blended veggies every day in a green smoothie and if I was having a glucose response I’d certainly know about it. The fatigue I always experience when ingesting even small amounts of glucose is unstoppable. Instead, when I eat my smoothie, I have my typical keto smooth ongoing energy. There’s tonnes of fiber in it, yet no glucose response in me.

My question is about fiber, glucose and to work out what, exactly, is the metabolic events between fiber and glucose absorption that Westman is referring to (in the absence of a glucose source).


For me, there is a difference between liquified kale versus whole kale, for example. Liquified veg and fruit is basically turning whole foods into processed foods. Doesn’t matter if I process it or buy it processed from the store. I digest whole and processed foods differently.


Fair enough, but where is the glucose coming from and why?


If you reread my initial question you’ll see it’s about how fiber is absorbed as glucose. That was Westman’s statement. I’m trying to figure out what he’s referring to. If what you propose is it then his statement is really poorly phrased, wouldn’t you agree?


I think it is very possible that breakdown of fibre into more digestible components happens. Is there a mechanical issue at play here? I dunno. Like greater surface area for chemical attack when veg is Liquified.


Is that science or speculation? My understanding is that there are only two routes for fiber.

  1. it is insoluble and undigested. period.
  2. it is soluble and is digested by the gut biome, releasing essential fatty acids. period.

Can you show me the science for anything else?

I’m seriously interested.

p.s. Also, I have no issue at all with blended (not liquified) veggies. Actually, they feel easier on my digestion. I also have processed chlorella powder and that goes down a treat too. So each of us respond differently I guess. Still, no clarity on the glucose issue though.


Overall I think you are having a different discussion to the one I am interested in. It seems like a worthy discussion but it is just not the one I am asking about in the thread.

I am asking about Dr. Westman’s statement about glucose from fiber. If what you are saying is connected to that I don’t mind the speculation but can you make it clear to me at which point you think glucose is coming into play?


I have the same response to vegetables that are liquefied versus eaten whole because I tried to use my blender to convert a salad I was eating into a breakfast shake and was dumbfounded at the time why I couldn’t eat it without what felt like eating carbohydrates, but in retrospect it makes sense. I tried it multiple times to confirm the result.

I’m highly speculating, but I think it’s related to intestinal flora, which are supposed to only be able to generate fatty acids from fiber, somehow influencing the rate of gluconeogenesis, not through conversion to glucose, but through one of the other mechanisms involved in digestion. For example, our gut flora produce about 90% of the neurotransmitter serotonin so what else are those little buggers doing?

We’re only beginning to understand the enormous impact of the microorganisms that we carry along in our gastrointestinal tract and although it’s easy to point a finger at something that’s emerging and barely understood, it also seems likely to explain what otherwise appears to be inconsistent and contradictory to what’s known about fiber digestion.

In other words, on the surface it appears that fiber is being absorbed as glucose, but it’s only an indirect effect - whatever the mechanism, it’s real in me and I’ll get whatever fiber I consciously include in my diet from unprocessed sources.


Fiber comes in so many forms, some decrease glucose levels and like Dr.Westman says some contain glucose, I believe pectin and cellulose to name a few. If you need to keep ketones high for medical reasons various fiber could be a problem but otherwise i’d rather have a healthy gut from feeding it a variety of prebiotic fiber than care about my millimolars.

Do you ever use ncbi? If you search glucose and fiber you get over 44000 results. Didn’t go deep but looks like all the info you are looking for is in here.