Everything You Need to Know about Fiber
What is fiber?
Fiber is a nutrient found only in plant-based sources. It’s found in vegetables, fruits, and whole grains; not in meat, poultry, fish, or dairy. (Just one more reason to ensure you’re eating lots of veggies!) Fiber falls under the umbrella category of carbohydrates but doesn’t get broken down into sugars like most other carbs. Our inability to fully digest fiber is what makes it so useful to our bodies! It supports healthy digestion, promotes heart health, helps balance sex hormone levels, and can even reduce the risk of certain cancers.
There are two main types of dietary fiber: soluble and insoluble.
Soluble fiber dissolves in water. These foods become gel-like when exposed to water or liquids and are fermented by the bacteria that live in your colon (essentially feeding your microbiome). Soluble fiber helps balance cholesterol levels and blood sugars, and supports digestive health.
Examples include: oats, barley, ground flax seed, chia seed, pysllium husk powder, sweet potatoes, pears, apricots, sweet potato, avocado, beans and legumes, and most vegetables.
Insoluble fiber does not dissolve in water. It remains unchanged on its way through your digestive tract, but can also be fermented by the gut bacteria in your colon. Insoluble fiber bulks stools to reduce constipation.
Examples include: beans, lentils, whole grains, nuts and seeds, bran, and some vegetables.
Many foods contain both soluble and insoluble fiber.
What does fiber do?
Fiber is an important part of any diet since it has many beneficial actions within the body.
Digestion
Fiber is probably best known for its contribution to bowel regularity and prevention of constipation. It helps you poop by promoting stool bulking and regular movement of your intestines. Soluble fiber can also be helpful to reduce diarrhea and IBS symptoms.
In addition, fiber signals your body to slow down the digestive process. This slows down the absorption of sugars from your food to prevent fast blood sugar spikes (which are followed by sugar crashes), and also helps you realize when you’re full.
Cholesterol and Heart Health
Soluble fiber (the type that becomes gel-like in water) reduces total and LDL cholesterol levels, while leaving HDL cholesterol levels unchanged, creating a favourable profile for the prevention of heart disease. It does this by reducing the amount of cholesterol absorbed from the diet, and increasing the amount of cholesterol excreted through bile (a digestive juice).
Hormone Health
Fiber intake (particularly ground flax seed) modulates circulating estrogen levels, making it a potentially helpful addition in conditions often related to imbalanced estrogen levels - PMS, heavy periods, and menopause.
Immune Health
Your digestive tract is one of your first lines of defense and a large portion of your immune activity is tied to your gut. When fiber is fermented by the gut bacteria, it feeds those bacteria, which are an important component of your immune system. Fiber has also been shown to interact with receptors on the cells lining the digestive tract (called epithelial cells) to turn on or modulate immune responses.
Cancer Risk
Dietary fiber intake is inversely related to colon, ovarian, and breast cancer. This means a higher fiber intake (to a point) is related to a lower cancer risk for those specific cancers.
How much fiber should you be eating?
The World Health Organization recommends a minimum of 25g of dietary fiber per day. I usually recommend 25-35g/day for my patients. Of course, your needs are individual and you may require some experimentation with total fiber intake or fiber types to help you feel your best. If you eat too much, you’ll likely experience bloating and abdominal discomfort. It’s best to increase your intake slowly to prevent these undesired effects.
I get my patients to track their fiber intake for a few days then calculate their daily average. Apps like MyFitnessPal have built-in counters and will also help you understand what foods the fiber is coming from in your diet.
Do you need a fiber supplement?
Most people don’t need a fiber supplement. You can get all the fiber you need from whole food sources. When you get your fiber from food, you automatically get all the other nutrients (vitamins, minerals, etc.) that are naturally packaged alongside the fiber. We’re constantly learning about the intricate relationships between nutrients (eg. how one nutrient helps your body make use of another) so it makes sense to get as much from whole foods as possible.
In some cases, fiber supplements can be helpful. This should be discussed with your healthcare provider, and an attempt to increase fiber intake from whole foods in your diet should be undertaken first.
If you do decide to take a fiber supplement, look for one from a reputable brand, without added sugars or a long list of additional ingredients. And don’t take it alongside your other supplements or medications since fiber can slow down medication absorption, just like it slows down food digestion.
Top Fiber Foods
Here are a few of my favourite fiber-rich foods, the ones I recommend to patients all the time.
Avocado (9g per medium avocado)
Raspberries (8g per 1 cup)
Green peas (9g per 1 cup boiled)
Lentils (15g per 1 cup boiled)
Chia seeds (10g per 2 tbsp)
I also frequently recommend My New Roots’ Life Changing Loaf of Bread to boost fiber intake. There are many other fiber-rich foods to explore, and a variety is best.
This article is intended for educational purposes and should not replace consultation with your healthcare provider.
REFERENCES
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Farvid MS, Spence ND, Holmes MD, Barnett JB. 2020. Fiber consumption and breast cancer incidence: A systematic review and meta-analysis of prospective studies. Cancer
Huang X, Wang X, Yu S. 2018. Association between dietary fiber intake and risk of ovarian cancer: a meta-analysis of observational studies.
Ma Y, Hu M, Huang P. 2018. Dietary fiber intake and risks of proximal and distal colon cancers. Medicine (Baltimore) 97(36):11678.
Moayyedi P et al. 2019. Canadian Association of Gastroenterology Clinical Practice Guidelines for the Management of Irritable Bowel Syndrome (IBS). Journal of the Canadian Association of Gastroenterology. 2(1):6-29.
Parikh M, Maddaford TG, Pierce GN. 2019. Dietary Flaxseed as a Strategy for Improving Human Health. Nutrients 11(5):1171.
Soliman G. 2019. Dietary fiber, atherosclerosis, and cardiovascular disease. Nutrients 11(5):1155.
Surampudi P, Enkhmaa B, Anuurad E, Berglund L. 2016. Lipid Lowering with Soluble Dietary Fiber. Current Atherosclerosis Reports 18(12):75.