A human need for fiber?

Well after attending AHS 2012 the other week I came home with more questions then I could have imagined going into it.  All of the presentations were fantastic, however the safe starches panel seems to be the most talked about.  This was very interesting, as it seemed like the panelists covered almost the entire spectrum of a carbohydrate intake continuum.  Another point that was brought up was the need for dietary fiber, and, being somewhat unsure about this topic, I decided to dig a little further into it.

What is dietary fiber?

When we talk about dietary fiber we are really talking about 2 different types of fiber: soluble and insoluble.  Soluble and insoluble are pretty straightforward; the soluble can get dissolved in water while the insoluble cannot.  However, the most important thing about fibers is that they are impossible to digest by humans alone.

When you ingest normal carbohydrates (and fibers are just select varieties of carbohydrates) they get broken down into single sugar molecules and absorbed through your small intestine.  Fiber, on the other hand, cannot be broken down by our intestines this way, and instead either passes straight through your gut undigested, or is digested by some of the millions of bacteria in your large intestine (note that this means they make all the way through the small intestine before anything happens to them)!  When this happens, they are metabolized by the bacteria and returned to the large intestine as short chain fatty acids, the most common being butyrate, and can then be absorbed and used as fuel by your body.  I think it is interesting to note here that Paul Jaminet, of Perfect Health Diet, says that you should count non-starchy vegetables as a fat source, since their main carbohydrate is fiber, and thus will be absorbed and burned as fat.  When the fiber just passes through your intestines unchanged it will help you to retain water in your digestive tract, and this is one of the ways fiber helps to ease constipation.

Why do we need dietary fiber?

Well this is where things get a bit a tricky.  Do we really need dietary fiber?  As I mentioned before your gut bacteria do the lion’s share of the work in breaking down fiber, and as such it plays a big role in keeping your gut happy and healthy.  And, you don’t have to look to far these days to find papers showing just how crucial gut health is to overall health.  So, fiber can be beneficial in this way.

What are the other benefits of fiber?  Well if we head over to Mayo Clinic we find this helpful article touting all the benefits of fiber.  The first two they mention I have already discussed, helping to keep you regular and helping maintain a healthy gut.  I would say many of the weight loss and blood sugar lowering effects of fiber could be attained by most people simply by switching up their eating habits to eat whole foods to satiety and only when hungry.  Fiber can definitely help with these goals, but are they the only way to achieve them?  Most certainly not.  So for their final point that fiber helps to lower cholesterol.  Well this is based on the assumption that cholesterol is truly the evil that most people think it is, which is simply not true.  Peter Attia had an amazing presentation at AHS that talked about how your LDL-C (LDL concentrations in the blood) levels are not all that important in determining CVD risk, but LDL-P (actual LDL particle numbers) are the better risk factor for determining your CVD risk.  Most of the studies performed to date have only been measuring the effects of fiber on LDL-C numbers, rather than the LDL-P numbers.

So, with all that being said, I think it is pretty hard to say that there is a “need” for a human to eat fiber.  Many of the so called health benefits of fiber can be accomplished in other ways, or may be slightly misleading either way.  In fact, this study from 2011 says that the amount of fiber might not be important all, but the viscosity of the fiber you eat is.

What to do about fiber?

After this closer look at fiber, I would say that humans do not have a need for a certain amount of dietary fiber.  There are some health benefits to eating fiber, such as maintaining a healthy gut bacteria population, and helping to keep you somewhat regular.  But both of these can be accomplished other ways.  Eating a whole food diet to satiety will help aid in weight loss, control blood sugar, and help to keep you regular without having to worry about how many grams of fiber you are eating everyday.  That being said many of our favorite whole foods are full of fiber, and so it shouldn’t be hard to get the benefits of fiber when eating this way.  All of the vegetables we eat will contain some amount of fiber, and plant foods should be a large part of diet, so I think most people should have their fiber need covered.