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Is soluble fiber sabotaging your LC efforts?

Expert Low-Carber

I've been doing a lot of research on fiber over the past week or so in an effort to sort out the "bottom line" of fiber, carbs and calories. I invite constructive criticism of the conclusion I have come to -- I actually hope to be wrong on this! -- but that conclusion isn't going to be good news to a good many ears here.

That is that 1 g soluble dietary fiber (SDF) = ~ 0.5g net glucose carbs!

Insoluble dietary fiber, IDF, passes through the human digestive system unchanged so it is non-nutritive in all aspects. Further, since it adds bulk to food and assists in stool formation and "moving things along" IDF can reduce the nutrient absorbtion from the food we do eat. Bonus for just about anyone wanting to lose weight regardless of the strategy employed. (I know this is gross, but think corn on the cob )

But as I've learned (thanks Jimmy!) recently, SDF may not be metabolized by the body, but it is fermented in the large intestine to short chain fatty acids (SCFA) that are absorbed in the large intestine and metabolized. Some of these SCFA's are used by the intestines themselves as fuel, but the rest go mainly to the liver to be metabolized.

The "joys" of SDF are many from a weight loss and general health POV. To list a few I've read we have:
  • When SDF absorbs water it swells forming a gel. This gives a feeling of fullness in the stomach and slows the progression through the digestive tract so you may feel full longer.
  • This slowing of the digestion has been shown to improve the stability of BG levels in diabetics.
  • SDF's are fermented in the large intestine to produce short chain fatty acids (SCFA's) that can be used by the intestine's cells as well as absorbed by the body. These SCFA's are believed to help with irritable bowel syndrome (IBS) by boosting the mucosal cells and perhaps reduce colorectal cancer risks. They are also believed to contribute to lowering LDL levels.
  • SDF's do have a smaller than normal caloric nutritive value to us humans as compared to other carbs (1.5 cal/g to 2.5 cal/g, so I'll use an average of 2 cal/g)

So far so good, right?! Well the curious scientist in me was interested in what is to become of all the SCFA's. We hear "fatty acid" and presume these are metabolized like other dietary fats, so eating soluble fiber has all the bennies above plus they are like ingesting fats!

Not so fast, unfortunately.
As it turns out, the SCFA's produced from SDF's are prime substrates for gluconeogenesis!!

According to this http://books.google.com/books?id=y2rvBwM...#PPA141,M1 (which focuses on inulin type SDF's) the major byproducts of SDF fermentation are lactate (15%) and SCFA's (40% of which these are further classified as approx 15% butyrate, 28% propionate & 67% acetate respectively). The SCFA's are absorbed or otherwise utilized for energy at a rather high 90-95% rate, and the latter two are either entirely (propionate) or partially (acetate) metabolized by the liver to PRODUCE GLUCOSE via gluconeogenesis (and lactate is also listed as a substrate for gluconeogenesis). Scroll down at this citation.

I have read several reports here (including KlediKlutz's ongoing experiments now including Julian bread) of BG increases with low carb breads and pastas. And, of course, the numerous reported stalls many seem to experience when including these products in their diet. This may well be why. Those "fibers" are like eating half their grams in sugar.

But wait!

It gets worse It turns out that, like all bacteria, the population will increase when their food supply increases. So more SDF is feeding these. Sounds great for digestion, but these same bacteria also ferment something else -- "regular" carbs that have not been completely digested previously. So in addition to adding to your carbs, you are very likely increasing the digestion/absorbtion of the other carbs in your diet. WHAMMO For those who may stall on soluble fiber, at least be consoled that you have a healthy and efficient digestive system

There may well be some mitigating factors to this in terms of the inefficiency and/or energy requirements for the gluconeogenesis pathways for these substrates, but to me it seems pretty clear now that soluble fibers should NOT be subtracted on a 1:1 ratio to find net carbs. At best they could be subtracted as 1:2. Here's a link to one source of fiber content for a pretty good sized list of foods: http://huhs.harvard.edu/assets/File/OurS..._Fiber.pdf

So my apologies for saying that those that go by total carbs were really just VLC, because that statement was based on the simplified view of fiber being totally non-nutritive. Now I know better, and total carbs may be the way to go with low carb products that contain high levels of soluble fiber -- my now beloved shirataki noodles are entirely SDF. I mostly stay away from the "frankenfoods" (any baked goods to this point are made with natural fibers), but everyone should also beware of things like polydextrose found in a lot of LC goodies that are classed as a soluble fiber and may therefore be contributing to your carb intake. Also, flaxseeds are about 1/3rd soluble fiber so are not the essentially carb-free food they are thought to be.

So if you're finding low net carbs isn't doing it for you, you may want to take a look at the *kind* of fiber being subtracted out to calculate that net result. Surely this is why Atkins suggested getting most of your carbs from non-starchy veggies because that fiber is mostly IDF.

Senior Low-Carber

Velly Intellesting !!!!!!!

Mackay Rippey
Are you Yin or Yang?

Advanced Low-Carber

I go back to GCBC by Gary Taubes and his take on fiber (that it is unnecessary). I'm a big believer in MORE FAT for bodily functions and not fiber. Early man did not forage for flax seeds to stay regular.

As for the Frankenfoods, well, they should be avoided for the chemical content alone!

Thanks for a great post Low Carb Cheater!

Expert Low-Carber

Things that make you go Hhhhhhmmmm!


"Never eat more than you can lift."
--Miss Piggy


Excellent analysis, LCC! You are a GREAT teacher of this stuff. So when's your blog coming?

Jimmy Moore, "Livin' La Vida Low-Carb Discussion" forum owner
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Advanced Low-Carber

Very, very interesting! Thanks for doing all this research and reporting on it for us.

I have come to really like the shiritaki noodles. Based on this analysis, I'm going to do a blood-glucose test with them (maybe this coming weekend). I think I can probably eat them without any sauce on them.

I also want to do a test with nothing but Splenda-sweetened water.

I'll post the results when I'm done.


Jim Elwell

Expert Low-Carber

I have come to really like the shiritaki noodles. Based on this analysis, I'm going to do a blood-glucose test with them (maybe this coming weekend). I think I can probably eat them without any sauce on them.

I also want to do a test with nothing but Splenda-sweetened water.

I'll post the results when I'm done.

I'll be interested in your results. I've been doing BG testing and my levels are so all over the map (but well within normal except I think my morning levels are a bit high) I don't think it would tell me anything to do an experiment.

FWIW, I haven't consciously cut down on soluble fiber, but since I started IF, I just don't have the number of meals to work in the "variety" -- result is I've been eating less flax and only had shirataki once. I'm not convinced that this was the cause of my stall, but I have had a bit of a "whoosh" w/o as much soluble fiber. Still -- even if you counted total carbs in the shirataki I find it hard to believe these "nothing" noodles could really impact weight loss by much! Now that I've developed a taste for them I'm not willing to give them up so fast either!

Advanced Low-Carber

WOW, what a revelation! Thanks for taking the time to post this valuable information. Was Taubes of the opinion that all dietary fiber is worthless....including insoluble fiber? Should we be still using insoluble fiberfor regularity & colon health? O.K., so now that we know that insoluble fiber grams count as some carbs.... it will be more difficult to count and keep carbs low. arggh!!!! Fiber was free, now it's not!


Expert Low-Carber

BTW, THANKS all for the positive feedback gang! I'm a researcher by nature and once I come across something that seems open ended I become almost obsessed. I'm glad sharing what I've discovered so far has raised a few eyebrows!

Advanced Low-Carber

didnt jimmy have an interview with someone on fibre? Wondering if one should quit net carbs, just do straight carbs? hummm

Advanced Low-Carber

well I found the episode but jimmy wasnt happy with him as he bashed Dr Atkins and to quote jimmy he is "a few frys short of a happy meal" LOL

Newbie Low-Carber

could someone point me to the interview or tell me how to search for it?


Advanced Low-Carber

Ew, that sounds so gross! ;-) But I'm interested to hear what the results are!


Expert Low-Carber

Dr. Bernstein says to only subtract half the fiber, but has admitted this is based on a gut-level feel. Sounds like he might be right.

Sugar is the enemy; fat is my friend. The only bad fats are artificial fats.
Low Fat & Fat Free -- tastes bad, bad for you.

Junior Low-Carber

I found the information very helpful. I bet soluble fiber has hindered my weight loss. I was probably consuming too many carbs thinking it was okay because I was subtracting the fiber.

Newbie Low-Carber

I've done a little more reading on the topic because it interests me.

I've learned:

(1) the short chain fatty acids produced from the metabolism of soluble fiber can actually inhibit the fat burning process (in other words, slows the rate of fat loss during dieting)

(2) The Julian bread people state that the fiber in their Smart Carb bread is mostly the insoluble type - so I guess that is a good thing, BUT if a company is going to stake their business on a nutritional claim- why not put that information (soluble vs. insoluble) on the product label so as to boost their legitimacy?? (some cereal boxes already do this).

I just hate to see people jumping on bandwagons and buying into marketing hype without all the necessary data to decide whether a product is good for them or not.

Aren't shirataki noodles basically all soluble fiber?


Expert Low-Carber

I believe that all products promoting any sort of carb reduction should be required to provide the soluble and insoluble content. The carbs DO add up at some point.

Quote:Aren't shirataki noodles basically all soluble fiber?

Yes, but this soluble fiber absorbs so much of its weight in water that a full bag contains like 3g total for the 1 net carb kind or just 3g total soluble fiber carbs for the konjac version w/o tofu. I don't sweat it to have a pack or two of these a week. Compare to many low carb wraps and breads where you can have 10g, 15g or more of fiber. Julian lists 12g/slice, if half of that fiber is soluble, then it's really about 4 net grams carb/slice instead of the 1 advertised. If you're eating one slice that's probably not going to derail you. If you're eating 2 or 3 those will really add up! And if we're talking more soluble fiber ...

My current compromise is that if I have any "product", I count 1/2g carbs for every g of fiber and if I'm within my target carbs I don't sweat it. But I would rather overestimate than underestimate!


This is really interesting! Thanks for sharing! I'm going to start looking at fiber very closely from here on out.

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Senior Low-Carber

Here's a link to Jimmy's podcast with Monastyrsky:
Episode 199 - http://livinlavidalowcarb.com/blog/?p=2988

It was certainly "interesting".
A pity the guy was so off the wall because he has some interesting stuff to say on his website.

Thanks so much for this discussion - has me thinking - and diving back to the original Atkins book which, I think, didn't talk about net carbs.



**Beating carbohydrate cravings is the most liberating feeling there is!**

Advanced Low-Carber

>>A pity the guy was so off the wall because he has some interesting stuff to say on his website.<<

Just wondering if anyone here has read Monastyrsky ‘Fiber Menace’ Book? I read over some of his ideas on the website and was just left with more questions; he does a lot of double talk. One second he is talking about how menacing fiber is and then later states that inulin and FOS are needed for healthy colon function. Maybe those who have read his book have a better understanding of what his message is....or maybe not! He is WAY out there, no doubt! He doesn't seem like he ever gets to the point! His bashing of Atkins and other low carb programs leads me to believe he is in to cutting others down to build himself up and sell his book. There may be some validity to what he has to say, if you can cut through his offensive demeanor!