What is the big deal with fiber? Even in the 70’s and 80’s it was a topic of TV commercials with Wilford Brimley and Euell Gibbons touting the benefits of eating oats and grains.
So what the heck is it and why do we need it?
Although it technically fits into the carbohydrate category, fiber contains no calories and is not a source of energy. It cannot be broken down by the digestive system so what is the point? Turns out there are several points and this group of compounds is critical to digestive health, which means it’s critical to health in general.
Fiber comes in three distinct varieties: insoluble, soluble, and resistant starches. You may recall from high school biology that plants have cell walls that form a sort of skeleton for the plants. These cell walls are made of cellulose and hemicellulose and make up insoluble fiber. They are called insoluble because they do not dissolve in water and cannot be digested. Soluble fiber and resistant starch compounds are also present in these plant cell walls. All three types of fiber are exclusively found in plants. Animal products do not contain fiber.
So, you may ask, why do we need to eat them if they can’t be digested?
Insoluble Fiber
The human body is cleverly designed to be self-cleaning. It has a handful of elimination pathways to get rid of what it doesn’t need including compounds that may do it harm loosely called toxins. Bowel movements are one of these elimination pathways. Insoluble fiber helps to form stool and clean up the intestines which is an important health function especially now with the abundance of toxins in our food and environment. When we do not have regular bowel movements, the waste material can sit in the intestines not only causing discomfort and sluggishness, but also allowing toxins in the waste to be reabsorbed into the bloodstream where they can wreak havoc. Insoluble fiber allows the body to gather those toxins along with other waste products and form stool that can be readily pushed out of the body.
And what about soluble fiber?
Soluble fiber also comes from plants. It includes compounds such as lignans, inulin, mucilage, pectin, psyllium, and resistant starch. If you’ve ever made your own jam, you’ve likely used the soluble fiber, pectin, to allow the jam to thicken and set. Soluble fiber acts in much the same way in the body. It absorbs water and creates a gelatinous mass in the intestines helping to form stool.
Blood sugar control
This gelatinous mass helps to slow the digestion which in turn slows down the absorption of sugar thereby regulating the blood sugar and preventing blood sugar spikes and drops that can mess with your energy levels and moods. Prolonged blood sugar spikes can lead to insulin resistance, prediabetes, and type 2 diabetes. Blood sugar spikes also create a vicious cycle that results in weight gain. Because the brain needs a constant supply of glucose and can’t handle blood sugar spikes, it responds to blood sugar spikes with a need for more glucose. It then tells the body it is hungry which results in more blood sugar spikes, overeating, and weight gain. By slowing digestion and allowing a gradual absorption of glucose, soluble fiber helps to avoid this cycle. Slowing digestion also means that food stays in the stomach longer which means you feel more full and satisfied. Soluble fiber also helps to regulate hormones that trigger hunger and satiety. It decreases ghrelin, the hunger hormone, and increases GLP-1 and other satiety producing hormones. The overall effect of consuming soluble fiber is better blood sugar control, weight loss, and better weight management.
Heart health
Did you know that soluble fiber promotes a healthy heart?
Soluble fiber binds with fats in the digestive tract allowing them to be excreted in the stool instead of being absorbed into the bloodstream. This lowers the low-density lipoprotein (LDL) levels in the body. LDL cholesterol is associated with atherosclerosis, heart attacks, and strokes. Thus, soluble fiber lowers the risks of these cardiovascular issues. Soluble fiber also aids the heart by helping to regulate blood pressure. Because being overweight is a risk factor for heart issues, soluble fiber’s positive effect on weight management also contributes to heart health.
Gut health
Similar to insoluble fiber, soluble fiber adds bulk to the stool, preventing constipation and readsorption of toxins. In fact, psyllium, a soluble fiber, is one of the primary ingredients in many constipation medications. Beyond being a bulking agent, certain soluble fiber acts as prebiotics in the gut. Prebiotics are food for the gut microbes. This food allows the beneficial gut microbes to flourish and harmful microbes to diminish, creating a healthy microbiome and preventing and reversing dysbiosis. These beneficial bacteria then produce more short-chain fatty acids (SCFAs). SCFAs are important for the immune system, improve the gut lining, and promote the production of anti-inflammatory proteins. Thus soluble fiber’s role in improving the gut microbiome also improves immune function.
And what about resistant starches?
A third class of fiber is resistant starch.
Starches are a type of carbohydrate that is broken down in the small intestine to release glucose into the bloodstream. Resistant starch, however, is a starch that resists this breakdown process in the small intestines. Instead it travels through the small intestines to the large intestine where gut microbes use it as a prebiotic and ferment it. A by-product of this fermentation is SCFAs. As noted in the discussion of soluble fiber, SCFAs promote a healthy gut and immune system and are used in numerous processes. Resistant starches promote the growth of beneficial microbes which in turn creates an environment that is inhospitable for disease promoting microbes. This creates a healthy robust gut microbiome. In addition, similar to soluble fiber, resistant starches improve blood sugar control, promote fullness, reduce constipation, decrease cholesterol, and reduce the risks of colon cancer.
We’ve established the fact that all three types of fiber, insoluble, soluble, and resistant starch, are health superstars. Now the question is…
How much do you need and how do you get it?
The recommended daily allowance (RDA) established by the FDA is 28 grams per day based on a 2000 calorie diet (approximately the calorie intake of an average healthy adult). Most Americans fall well short of this goal only consuming 10-15 grams per day and for many that is with a much higher intake than 2000 calories. That’s less than half of what is recommended! No wonder some nutrition gurus believe that constipation is a national health crisis with over 4 million people experiencing frequent constipation. We need to drastically increase our fiber intake. Since we get fiber from plants, that means increasing our consumption of plants, another shout out to a plant based diet!
Sources of insoluble fiber include whole grains, nuts, beans, cauliflower, green beans, and potatoes. Sources of soluble fiber include fruits and vegetables (especially with skins), oats, peas, citrus fruits, barley, psyllium husks, chia seeds, and beans. The following is a list of high fiber fruits, vegetables, grains, and legume:
- Raspberries 8 g/cup
- Pear 5.5 g/1 medium
- Apple 4.5g/ 1 medium
- Banana 3 g/1 medium
- Green peas 9 g/ 1 cup
- Broccoli 5 g/1 cup
- Brussel sprouts 4.5 g/1 cup
- Baked potato with skin 4 g/1 medium
- Corn 4 g/1 cup
- Barley 6g/1 cup
- Quinoa 5 g/1 cup
- Rolled oats 8 g/1 cup
- Brown rice 4g/1 cup
- Split peas 16g/1 cup
- Lentils 15.5g/1 cup
- Black beans 15 g/1 cup
- Other beans (navy, cannelloni, great northern) 13g/1 cup
- Almonds 3.5g/1 ounce
- Sunflower seeds 3 g/1/4 cup
Resistant starches are present in beans, peas, lentils, and whole grains, but they are also found in:
- Plantains
- Green bananas
- Cooked and cooled rice
- Cooked and cooled potatoes
As you can see, legumes and beans are the heavy hitters when it comes to fiber. You can easily get most of your daily requirement of fiber in a quinoa bowl with a cup of quinoa, a cup of black beans, and a topping of veggies. Or you can get at least half way there with a baked potato and a variety of roasted veggies such as broccoli, brussels sprouts, and cauliflower. To increase the amount of resistant starch you can cook, cool, and reheat the potato. Add in a cup of raspberries and pears topped with some almonds or sunflower seeds for dessert and you are well on your way. How about a fiberful bowl of homemade muesli with rolled oats, dried apricots bits, raisins, and sunflower seeds? Check out my recipe for Vegan Quinoa Bowls for a healthy dose of fiber in a delicious meal.
How can you tell if you are getting sufficient fiber?
This may not be a topic you’d like to discuss, but it’s an important one and a good measure of adequate fiber. Healthy humans have at least one bowel movement (BM) a day. The type of BM you are having is also important and indicative of your health. Consult the Bristol Stool Chart and aim for type 3 or 4. If you are not having the frequency or consistency of BMs, think hydration and fiber. One important thing to note is that adequate hydration is paramount when increasing the fiber in your diet. See the above list, but other fruits, veggies, legumes,and whole grains will also contribute to your fiber intake and hydration. Be sure to include leafy greens, citrus fruit, sweet potatoes, and a wide variety of other plant foods in your diet. Recent studies have shown that a diverse microbial population in the gut is directly linked to better health. Consuming a variety of fiber rich foods improves microbial diversity.
Consider including high water content fruits and vegetables into your diet to help increase water consumption. Watermelon, celery, cucumbers, lettuce, and tomatoes are great examples of high water content foods.
In a nutshell…
As you can see, fiber is an incredible health aid and is much more than just filler. It improves digestion, aids in toxin elimination, reduces LDL cholesterol, helps manage diabetes, improves coronary health, manages weight, promotes a healthy gut microbiome, improves immune function, and reduces the risk of colon cancer. Insoluble fiber helps move things along the digestive tract and clears the intestines of debris. Soluble fiber helps to bulk the stool and feed the gut microbes. Resistant starches also feed the gut microbes creating a healthy microbiome and health-promoting SCFAs. A healthy gut is the cornerstone of a healthy human. And fiber is the gut’s BFF.