Dietary Fiber - Friend or Foe? Addition of Hydroxpropyl-Methylcellulose, a Non-Fermentable Viscous Fiber, to Standard(!) Rodent Chow Reduces Fat Gain by -22%

Image 1: Just as about everything, these days, you can buy the semisynthetic non-fermentable viscous fiber Hydroxpropyl-Methylcellulose pound-wise from China - this is probably also where the producers of the junk food you hopefully are not eating get their E464 from ;-)

If the health and fitness community on the Internet was a battlefield (personally, I sometimes think it is ;-) one of the ongoing skirmishes would certainly be fought over the question whether the deliberate ingestion of great amounts of dietary fiber was a good or rather a bad thing. I must admit that I have not really made up my mind on the benefits and caveats of increasing or decreasing your fiber intake, partly because the available science appears to be quite inconclusive. This, obviously does not hinder the "ANTI faction" in the fitness and nutrition world to add "fiber" as the 1001 item on their never-ending list of ultimate dietary evils. My gut feeling does yet tells me this has more to do with the fact that mainstream dietary recommendations list dietary fiber as a "healthy food" to eat, than with a thorough research of the available literature, which has, as of lately, been extended by a particularly interesting study from scientists from the Department of Food Science and Nutrition at the University of Minnesota and the Pennington Biomedical Research Center in Baton Rouge, Louisiana (Islam. 2011).

When fiber ain't fiber, natural is not naturally better

Being aware of the partly contradictory results previous studies on the metabolic effect (as measured in the lab and not by the way your poo-poo looks or how often you have to go to the toilette, like the "experts" like to do it ;-), Ajmila Islam and her colleagues fed a group of 6 week-old male Wistar rats a standardized rodent chow (AIN-93G, composition see figure 1 in previous blogpost) with either hydroxypropyl-
methylcellulose (HPMC) or standard cellulose as a source of dietary fiber, which comprised 5% of the animals' otherwise totally identical diets. This obviously sounds nonsensical if you follow the usual black or white approach to nutrition (which btw. is propagated by the mainstream and the ANTIs, as well), after all fiber is fiber and should be good or bad!? Well, it turns out that there are more than subtle differences in

1. the viscosity of the fiber / fiber food mixture, and
2. the fermentability of different types of dietary fiber

Now, cellulose the main component in plant cell walls and "the fiber" most mainstream dietitians (and their ANTI opponents) have in mind, when they are talking about the beneficial / detrimental effects of "dietary fiber", is neither viscous nor readily fermentable. Hydroxypropyl-methylcellulose (HPMC) is also non-fermentable, but contrary to its naturally occurring cousin it has a high viscosity.

Hydroxypropyl-methylcellulose, short HPMC, is a semisynthetic, inert, viscoelastic polymer that is used as an ophthalmic lubricant, as well as an excipient and controlled-delivery component in oral medicaments, and has, under the disguise of the "E-number" E464, already found its way into a lot of commercially produced foodstuff, where it is used as an emulsifier, thickening and suspending agent, and as an alternative to animal gelatin.

While its artificial origin will obviously make the ANTI faction cry out loud, again, I suggest you first read about the effect HPMC had on the animals, before you totally discard it as being "not natural", "non paleo", "the work of Monsatan" or whatever...(btw. it is at least kosher ;-)

Figure 1: Changes in body composition (weights in g) after 6 weeks on standard diet with either non-viscous cellulose or viscous hydroxypropyl-methylcellulose as the primary source (5%) of dietary fiber (data adapted from Islam. 2011).

If you look at the data in figure 1, you will have to assert that the body composition of the lab animals did benefit from 6 weeks on the 5% HPMC diet. With a -29% reduction in the increases in purportedly "dangerous visceral fat", a -22% reduction in total adipose tissue gain and non-significant changes in lean mass accrual HMPC easily outperform the "Allis" and "Orlistats" of the pharmaceutical industry. Moreover, while the latter simply reduce the amount of dietary fat that is actually digested (an idiotic approach to weight loss, if you asked me), the non-fermentable viscous fiber in the Islam study worked its fat burning magic right via increases in AMPK, COX, citrate synthase, PGC-alpha, PPAR-delta and UCP3 expression, or, put simply: The 5% HPMC diet ramped up mitochondrial fatty acid oxidation.

Figure 2: Changes (relative to cellulose group) in gene expression in liver and soleus muscle of HMPC fed rats (data adapted from Islam. 2011).

Nevertheless, the slight, yet statistically significant smaller increases in bone density in the HPMC group (+6.4g vs. +7.4g) do suggest that in addition to these inert metabolic effect, the mere excretion of parts of the diets (with respect to bone density probably minerals like calcium and phosphorus), of which the animals in both groups consumed about identical amounts, could also have contributed to the otherwise beneficial effects of HPMC feeding, which, as the profound decrease (-41%) in liver PEPCK expression suggests, also included reductions in the hepatic rate of gluconeogenesis.

Figure 3: Changes (relative to cellulose group) in glucose metablism and adipokine expression of HMPC fed rats (data adapted from Islam. 2011).

The overall beneficial effects on glucose and fatty acid metabolism, by the way, are also reflected in the changes in blood glucose and adipokine concentrations I plotted in figure 3. The lower insulin and leptin levels in the presence of reduced body fat stores indicate increased insulin and leptin sensitivity and could be partly mediated by the marked increase in adiponectin expression, as the latter, as Islam et al. point out, has been found to have an "insulin sensitizing effect in both muscle and liver and a thermogenic effect (enhanced lipid metabolism) in skeletal muscle".

"Fiber is good, then! Right?"

Contrary to cellulose and fermentable viscous fiber, such as guar gum, of which a 2010 study by Isken et al. (Isken. 2010) found that it had, fed at 10% of the diet of mice, no effect on body fat levels in the short term (15 weeks) and even increased adiposity in the long-term (from 27 weeks to 43 weeks), short term feeding with 5% hydroxypropyl-methylcellulose (HPMC) exhibited unexpectedly profound beneficial effects on the metabolism of these otherwise healthy and normally fed (this is important, because we usually see fiber supplementation in the context of "high fat" diets) rodents.

Whether it would be advisable to deliberately look for the number E464 on the foods you consume is yet still highly questionable. For one, every food with an "E -number" on its ingredient list should disappear from your grocery list, anyways. I do not care which number it is, but if food has "E"'s in it chances that this is highly processed garbage are 99% and in that case the supposedly insignificant amount of HPMC will not turn junk into health food. And secondly, and certainly more importantly, we are just beginning to understand how the viscosity of the foods we eat and their susceptibility to fermentation interact and which impact(s) these characteristics have on our digestion and metabolism. After all, it could well be possible that, just as in the Isken study, this beneficial short term effects eventually fire back and the formerly lean HMPC rats suddenly start gaining weight (and body fat) like crazy... you see, as usual things are more complicated than the innocent (yet actually invalid) question "Is fiber good or bad?" might suggest.