Coffee, fiber, and neuroimmunity

While enjoying my coffee today, I pondered the research i’ve read on it and decided to come back to a paper from 2007 (1) that examined, of all things, its fiber content.

Polysaccharides, specifically type II arabinogalactan and galactomannan, have been identified in coffee.  Because they are largely indigestible, they are considered dietary fiber.  Food composition tables previously reported zero dietary fiber for coffee.  However, coffee contains many phenolic compounds that may bind polysaccharides and pass them from the bean to the brew.

So the investigators tested 2 ground Colombian coffees (70/30 mix of medium and dark-roasted, and a freeze-dried) using 3 extraction methods (expresso/food service industry coffeemaker, filter/drip electric coffeemaker, and freeze-dried/instant coffee).  They determined they soluble fiber, total phenolics, and antioxidant activity with the FRAP and ABTS assays.

The fiber content varied from .47 to .75 grams per 100 mL of coffee, and by preparation type from least to greatest: filtered, expresso, freeze-dried.

As noted by the authors, this is higher than other common beverages such as orange juice.

Compared to the average soluble fiber intake of about 7 grams per day in Spain (where study was performed), 3 cups of expresso is approximately 0.66 grams of soluble fiber, which is about 10% of the daily intake, which is more than what is likely perceived.  From my calculations, 3 cups (at 240 mL per cup) of freeze-dried coffee would be approximately 5.4 grams- a significant amount.  This could be an important source for the half of Americans of consume less than 15 grams of fiber per day.  Being completely soluble may be important as well – read on to the next section on neuroimmunity for details.

Because they used a process called dialysis to isolate the soluble fiber, they could measure the antioxidant activity of the phenolic compounds that were bound to the fiber compared to that which is not.  They found that a significant amount (~30-51%) were contained with the fiber.  This means that some of the compounds will be absorbed in the small intestine, but those bound to the fiber will only be accessible in the large intestine after the bacteria there ferment the fiber and release them.  I would assume this may have significance to colon health, including outside of coffee.

Soluble Fiber, Neuroimmunity, Sickness

A paradigm shift is occurring in inflammation-mediated sickness research that builds on a concept of neuroimmunity; the brain recognizes various cytokines produced in response to infection and responds with inflammatory products which translate to physiological symptoms, at a magnitude dependent on certain milieu (2).

In this regard, an interesting study (2) was published earlier this year on soluble fiber and its relation to neuroimmune function.  When soluble fiber is fermented, short-chain fatty acids are generated which have potential to modulate immune mechanisms.  Other research has found that soluble fiber can dramatically change the bacterial populations in the gut, and in fact is able to affect type I diabetes progression in a mouse model.

The investigators theorized that the immunomodulation from soluble fiber could be because it alters T-helper cell functions.  In particular, the cytokines such as IL-4, IL-5, and IL-13 are secreted from Th2 cells in response to bacterial toxins.  IL-4 represses Th1 activation; Th1 induces classically activated macrophages, which mediate “sickness behaviors” (classical sickness symptoms).  Instead, IL-4 induces alternative activated macrophages which do not respond as intensely to toxins, and enhances IL-1RA, which speeds sickness recovery.

Thus, they tested whether C56BL/6J mice would experience less sickness behavior (social withdrawal, fever, food intake, weight loss) when injected with an immune challenge (lipopolysaccharide) on a diet high in pectin, a soluble fiber, compared to cellulose, and insoluble fiber.  The diets consisted of either 10% pectin, 5% cellulose, 10% cellulose, or a commercial chow with 15% mixed fermentable and non-fermentable fibers, as pictured below.

The results show that the cellulose fed mice were more socially withdrawn, and had a slower recovery to LPS injection versus the commercial chow group.  Then the other diets were formulated to tease out which ingredient was responsible.  In subsequent experiments, they found pectin fed mice were less sick and recovered faster than cellulose fed mice.

As speculated, IL-4 and IL-1RA were upregulated in the brains (and for IL-4, gut) of pectin fed mice compared to cellulose fed.  IL-1beta and TNF-alpha were reduced in brains of pectin fed mice, which shows that Th1 activation was hampered.

Short chain fatty acids in the gut were also measured, and were significantly higher in the pectin fed group compared to cellulose fed.  Among them, butyrate, is a histone deacytelase inhibitor; histone acetylation enhances IL-4 expression thereby supporting the hypothesis that through fermentation of soluble fiber, IL-4 -> IL-1RA polarizes Th2 and induces alternatively activated macrophages, which reduces the proinflammatory response to the LPS challenge.

IL-4 knockout mice were resistant to the effects of pectin, and cytokine profiles were similar to those of cellulose fed mice.

Human Relevance?

The amounts of fiber on a relative dry weight comparison is within the ADA recommendation for humans of 25-38 grams.  This is the first study suggesting soluble fiber affects neuroimmunity, but other studies have found that it also ameliorates colitis and irritable bowel syndrome.  This study does not suggest that taking soluble fiber will necessarily help us; only that a diet devoid of it may cause an exaggerated response by the brain to infection.  Normal diets consist of both fermentable and nonfermentable fiber as plant cell walls are a combination of pectin and cellulose.

The previously discussed amount of soluble fiber in coffee does not necessarily do anything itself, but theoretically it could with a high enough coffee consumption.  Mostly, it was just an interesting finding to me, and is a lesser known soluble fiber contributer to human diets.   As always, the best diet is one that contains a high amount of plant foods, and this study provides another mechanistic reason why specific constituents are important for health.

References

1. Díaz-Rubio ME, & Saura-Calixto F (2007). Dietary fiber in brewed coffee. Journal of agricultural and food chemistry, 55 (5), 1999-2003 PMID: 17295507

2. Sherry CL, Kim SS, Dilger RN, Bauer LL, Moon ML, Tapping RI, Fahey GC Jr, Tappenden KA, & Freund GG (2010). Sickness behavior induced by endotoxin can be mitigated by the dietary soluble fiber, pectin, through up-regulation of IL-4 and Th2 polarization. Brain, behavior, and immunity, 24 (4), 631-40 PMID: 20138982