Written by Andrew Neff
Combatting weight-gain and reducing appetites with dietary fiber
Eating more dietary fiber promotes good health, and seems to make people feel full.
Different types of fiber may have different effects on our body.
Chitosan may be a good alternative, but more research is needed.
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Like 33 million other Americans, I recently found myself sucked into an Instagram hole - the Tasty channel. I watched from an overhead camera at 5X speed as sectioned potatoes were dunked in oil and dipped in mayonnaise, marshmallow frosting was poured over chocolate cake, a mass of cheeseburgers smashed between two large pizzas. Yum.
Understanding human appetite is a difficult prospect. A complex interplay of biochemistry and neurocircuitry has to situate itself within a hostile cultural environment where millions of dollars are spent maximizing the deliciousness of french fries. The supersized role food plays in our culture and economy highlights the difficulty we’re confronting with the obesity epidemic.
Amongst this barrage of environmental threats, it’s kind of amazing that we actually have some pretty simple medical approaches for reducing appetite. For example, FDA approved appetite suppressants like Belviq and Lorcaserin target neurotransmitters like serotonin, dopamine, and epinephrine. There are effective surgeries that implant balloons in the stomach or bypass it altogether. But then there is a tried and true approach that every attentive and health-conscious mother has been trying to push on us since we were kids - eating more dietary fiber.
Yes, it seems, eating more fiber can reduce appetite (Wanders, 2011). As the story goes, dietary fiber isn’t broken down by human enzymes; and so we chew, we crush, we surround with intestinal acids and digestive enzymes, but dietary fiber remains resilient, mostly in-tact and unabsorbed. In the 1970’s, Dr. Ken Heaton proposed that dietary fiber makes us feel full simply by occupying space in our gut.
Embedded in the wall of your intestines is a network of peripheral nerves. Some have receptors that are attuned to detect particular nutrients, some are simple machines capable of responding to intestinal stretching. As fiber sits in your gut, stretch receptors are activated, letting our brains know that they’ve had enough thank you.
But clearly, there’s a limit to fiber’s effectiveness. Most of the time, our pasta infatuated modern brain responds to intestinal fullness by pretending it didn’t hear anything. And this is 2019, fiber may be useful, but it’s about time for some optimization. You see, fiber is not a single thing, it’s an umbrella term used to describe all non-digestible carbohydrates. There are soluble fibers, fermentable fibers, viscous fibers, fibers that are made of digestion-resistant starch, fibers from grains and fibers from vegetables, and on the list goes. These fibers all have slightly different effects on the body, and therefore, you might expect, a different impact on appetite. Some seem to work poorly, some work pretty well, and some form the basis for multi-million dollar weight-loss products.
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Fiber Supplements and Long Term Weight Loss
If proven to cause weight loss, fiber supplement brands like Metamucil (Psyllium) or Skinny Shirataki Noodles (Glucomannan) stand to make a good bit of money. Fortunately for these brands, the mostly unregulated U.S. supplement industry doesn’t get in the way of them marketing weight-loss claims without a firm government-sponsored evaluation. So which types of fiber are, and which aren’t supported by research?
Psyllium is extracted from the Indian Plantago seed and is processed into the appropriately named, thick, gluey, mucilage. Gross. Branded as Metamucil (still gross), psyllium, as a type of dietary fiber, is associated with a range of health benefits, some of which are well supported by scientific evidence (Boeing, 2012). But when it comes to weight loss, a recent review of 22 randomized controlled trials showed that supplementing with Metamucil wasn’t any better than placebo (Darooghegi Mofrad, 2019).
Glucomannan is derived from the Asian Konjac plant, also known as the devil’s tongue. The konjac plant has a lot of culinary applications, including the somewhat strangely textured Skinny Shirataki Noodles. In europe, glucomannan is legally marketed as a weight-loss aid, but the data is ambiguous. In 2008, a review of fourteen studies showed that glucomannan contributed to an average weight loss of 1.5 lbs (Sood, 2008). However, a more recent review in 2015 used a more stringent criteria. From eight studies, they came to a different conclusion (Onakpoya, 2015).
Guar Gum is a powder extracted from the Pakistani Guar Bean. Its use is widespread in processed foods ranging from ketchup to ice-cream. As it relates to health, Guar Gum is another complex case. In 2001, a review of 20 studies found that Guar Gum, at the doses tested, did not have an impact on weight loss (Lewis, 1992). At the same time, given a large enough dose of any fiber (or anything), people say they start to feel full (Rao, 2016). At times, this can be a big problem, as in 1992, 18 instances of medical complications were reported to the FDA. It seems that Guar gum is so thick and sticky that it plugs up your esophagus or small intestines, at times requiring risky surgical intervention.
Chitosan is a material obtained from crustacean shells, and is used in a bunch of strange commercial applications including as a biopesticide, a wine-preservative, a paint-additive, an anti-bacterial agent, and, as a dietary supplement. In a review of 7 studies, all but one showed that Chitosan supplementation contributed to weight loss (Wanders, 2016). A separate review of 14 studies found that Chitosan reduced body-weight by an average of 2.2 pounds (Moraru, 2018). Unlike many other sorts of fiber, there seems to be little objection to the claim that Chitosan supplementation promotes weight-loss, albeit not a lot.
There are lots of other types of fibers, for example beta glucan, pectin, inulin, and resistant starch, all of which have proven to reduce body-weight in at least one study. However, it’s clear from the types of fibers that are well studied, there’s a lot of discrepancy between experiments, and a lot of remaining ambiguity. Some of this has to do with how much fiber people ate, how often they took the supplement, and what was used as a comparison condition. For these slightly more neglected fibers, the jury is still out.
But taking a step back, does the difference between fiber source really matter? To some skeptics, the differences between fiber-source as it relates to appetite and weight-loss isn’t important. All that matters, according to Dr. Heaton’s explanation, is that fiber clogs things up. It’s possible that there aren’t meaningful differences between fibers, but it neglects a really interesting possibility, which is a complex interaction with gut microbes. Different types of fiber with different chemical and physical properties will inevitably have a different impact on gut microbes. This could shape which organisms live in the gut (the prebiotic concept), which could then impact our health. Or, maybe, as our bacteria encounter different types of fiber in the colon, a unique blend of metabolites is created, which can then have a different impact on our bodies. It’s possible that fiber’s only real impact on appetite is through intestinal bulking, but it’s also possible that some fibers, say Chitosan, are having a subtle and complex effect on the gut microbiome, which is impacting our appetite in complex and mysterious ways.
At the same time, skeptics may also say that the magnitude of weight loss induced by fiber is too minimal to have a substantial clinical impact. Losing two pounds over a couple of months won’t make a real dent in the obesity epidemic.
Maybe so, but fiber’s not just about weight loss. Randomized controlled trials show that fiber has a beneficial impact on cardiovascular health (Boeing, 2012) - and the CDC recommends increasing fiber consumption as a means for decreasing cholesterol. A couple of pounds may not be a ton, but, our moms were right, fiber is good for our health, and when it comes to weight loss, maybe every little bit could help.
About the Author: Andrew Neff has his Ph.D. in neuroscience and is the founder of this blog. He lives in metro Detroit with his wife Lisa, son Samuel, and dog Carter.
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Andrew Neff ~ Sept '19
Neel Shah ~ Aug '19