Dietary Fiber: Beyond The Bathroom

When it comes to the wide landscape of diet trends and fads, we've seen it all. Low fat, high fat, low carb, no meat, all meat, all fruit, all plants, you name it. But what about high fiber?

While a varied plant-based diet would be high fiber by definition, those championing the health benefits of vegetarian or vegan approaches aren't exactly waving the fiber flag when stating their case. The reality is, many of the most commonly cited health benefits of plant-based diets (i.e. lower incidence of cancer, heart disease, diabetes, etc) can be directly tied to increased dietary fiber consumption.

That's right, fiber isn't just a supplement your grandfather takes to help him go #2. Dietary fiber does much more in our digestive tract than simply moving doodoo along. Through its critical role in nourishing our gut microbiome, regulating blood sugar levels, and the key part it plays in digesting fats, fiber is an unsung hero in reducing the risk of many lifestyle diseases that continue to plague our society.

Let's take a look at the two primary types of dietary fiber and the different ways in which they work in the body. Then, we'll get into why fiber consumption is important for overall health, beyond just your performance on the toilet.  Finally, we'll cover how to easily and regularly incorporate more fiber into your diet.

Soluble vs. Insoluble Fiber 

Fiber is broken down into two forms, soluble and insoluble. The major difference between the two is in the names themselves; soluble fiber is soluble (dissolves) in water, while insoluble fiber does not. Plant sources typically contain both types of fiber in varying ratios.

When soluble fiber enters the digestive tract, it attracts water and becomes a gel-like substance as it dissolves. This viscous gel slows digestion speed and actually ferments in the large intestine, becoming a nutrient source for beneficial gut bacteria. For this reason, soluble fiber is also known as "prebiotic" fiber, or the type of fiber that feeds and works symbiotically with probiotic bacteria. In addition, as soluble fiber ferments in the large intestine it releases what are called SFAs (short-chain fatty acids), a beneficial byproduct that acts as an energy source for cells in the colon. Common sources of soluble fiber include apples, cruciferous veggies (broccoli, brussels sprouts, etc), asparagus, and psyllium husk.

Insoluble fiber, on the other hand, passes through the digestive tract intact. It adds bulk and attracts water to stool, making it the go-to for easing constipation, promoting regular bowel movements, and intestinal health. It is found in foods like wheat or oat bran, beans, and nuts.

Benefits of Fiber Intake

• Immune Function

Soluble fiber plays a crucial role in supporting the health of the gut microbiome by feeding and helping propagate beneficial bacteria. Gut bacteria serve as the backbone of our immune system, so it is critical to maintain a healthy balance of microbiota. Regular fiber consumption aids this balance.

• Blood Sugar Regulation

Both soluble and insoluble fiber slow digestion speed and therefore slow the release of sugar into the bloodstream following the consumption of carbohydrates. This helps prevent a rapid blood glucose and insulin spike that can lead to a subsequent "crash" of energy levels and increased cravings. For this reason, fiber consumption is especially beneficial for the treatment and prevention of type 2 diabetes.

• Cholesterol Health

A major benefit of dietary fiber intake that doesn't get mentioned enough is the positive impact it can have on cholesterol numbers. Soluble fiber binds to LDL ("bad") cholesterol particles in the digestive tract and helps usher them out of our system. In addition, soluble fiber helps slow the reabsorption of fats from our intestines back into the blood stream, which also has a beneficial effect on serum cholesterol levels.

• Anti-Cancer

Another benefit that isn't brought up enough is the anti-carcinogenic effects of regular fiber intake. Both soluble and insoluble fiber may be beneficial for this purpose. The short-chain fatty acids produced by soluble fiber promote colon health and therefore decrease the risk of colorectal cancer. Insoluble fiber, on the other hand, acts like a street sweeper as it makes it’s way through the intestines, sweeping away potential carcinogens as well as potentially harmful bacteria.

Convinced adding more fiber to your diet might be a good idea? The good news is, upping your fiber consumption is relatively easy, because there are a ton of food sources to choose from! The lists below are not exhaustive, but may serve as a starting point:

Soluble Fiber                                                                

-Psyllium husk (typically as a supplement)

-Beans

-Flaxseeds

-Asparagus

-Broccoli/Cauliflower/Brussels

-Apples

-Pears

-Avocado

-Lentils/Legumes

-Peas

 Insoluble Fiber

-Nuts

-Wheat or oat bran

-Berries (Blackberries, Raspberries, Blueberries)

-Radishes

-Various whole grains (Barley, Quinoa, Millet, Oatmeal, etc)

-Potatoes

-Popcorn

-Beans/Lentils/Legumes

-Flaxseeds

-Avocado

And the lists go on. Note: there is overlap between the two lists, as many high fiber foods will contain both forms. As for recommended daily consumption, men should aim for a minimum of 30g or more per day, while women should be intaking at least 20g or more. If you're currently well below these totals (as up to 90% of Americans are) it's important to gradually increase fiber consumption. A rapid increase in fiber consumption can lead to gas, bloating, and general digestive discomfort. As fiber intake increases, it's also important to increase water/fluid consumption to ease the passage of these indigestible plant compounds through the intestines.

So there you have it, the hot new diet coming to an influencer near you. Let there be roughage.