THE THING ABOUT FIBER…
Most of us don’t think about fiber beyond that it helps us go to the bathroom. I certainly see that in my coaching practice, but when clients gain a better understanding of its role in many body functions–including brain function!--fiber becomes a much more interesting piece of the health puzzle. Learning how to incorporate it more strategically into your diet may even help you relieve random symptoms you might be dealing with.
Most of us don’t consume even half of what our ancestors did, about 100g a day. In fact one of the last hunter gatherer tribes in Africa, the Hadza, consume 100-150g per day. Most Americans consume only 8-15g per day! The USDA recommends that women consume 25g, and men 38g daily. Keep in mind that public health recommendations for nutrients are mostly based on the very minimum of nutrients required for health, and not on optimal levels.
It’s important to understand the different types of fiber, and to work with a health practitioner if you have digestive issues before increasing your consumption. When our gut is not healthy, high amounts of fiber can actually exacerbate symptoms.
FIBER PRIMER
Fiber is a complex carbohydrate, but it differs from other carbohydrates in that it moves through the small intestine undigested. Unlike other carbohydrates, it doesn’t get broken down into glucose. That's why you might hear about people who intentionally restrict carbohydrates, like on a keto diet, subtracting the amount of fiber from total grams of carbohydrates to obtain net carbohydrates. Of the total calories of a food that’s consumed, the ones that correspond to the fiber amount are not usable calories by our bodies, they are calories that are used by our microbiota (the microbes that live in our gut).
Fiber is digested in the large intestine by these gut microbes, producing short chain fatty acids like butyrate. Recent studies show that these might influence gut-brain communication and brain function directly or indirectly. Scientists are just beginning to understand the mechanisms by which these metabolites produced by the microbiota have an effect on brain physiology and behavior, how they impact the central nervous system, and how they affect our mood.
Another reason to love fiber is its role in metabolic health. Fiber helps us regulate blood glucose by slowing down the absorption of foods. Consuming fiber with every meal helps prevent large blood sugar spikes, and also helps with staying satiated for longer. Fiber also helps regulate cholesterol and hormone levels in the body.
The two main categories of fiber are SOLUBLE, and INSOLUBLE.
SOLUBLE FIBER
It dissolves in water and forms into gel. You've noticed this in chia, flaxseeds, and psyllium husks. It’s the type that gets fermented in the large intestine and produces the short chain fatty acids mentioned before. It increases the rate of bile excretion, which is key for regular elimination of hormones like estrogen and testosterone, as well as total and LDL cholesterol. I've seen amazing results from daily flax seed consumption in female clients who have menstrual cycle issues, PMS, and estrogen dominance. The fiber in these helps to bind and excrete excess hormones circulating in our body (there are other reasons beyond fiber for why flax works for regulating estrogen, but I’ll leave that for another newsletter).
Soluble fiber has subcategories:
Inulin (in sunchokes, artichokes, chicory)
Pectin (in berries, apples, citrus)
Beta glucans (mushrooms and oats)
Gums (guar, arabic, acacia).
Some of the richest sources of soluble fiber include beans, roots and tubers (without the peel). You've also probably heard of prebiotics; prebiotics act like soluble fiber and become “food” for our gut microbes. Most prebiotics are soluble fibers. Resistant starch (in green plantains, and in cooked and cooled potatoes, rice, and other roots) is a prebiotic that has both soluble and insoluble fiber.
INSOLUBLE FIBER
It doesn't dissolve in water, but helps with elimination by increasing the bulk of stools. It also ferments in the large intestine but not nearly as much as soluble fiber. This is the type of fiber that can exacerbate symptoms for people with digestive disorders (i.e. IBS). The roughage of insoluble fiber can irritate the intestinal lining of those with more delicate digestive systems.
Subcategories include:
Cellulose- it’s the main constituent in the cellular walls of plants, for example the stringy part of celery stalks.
Lignin- it’s in the middle as well as in the secondary cell wall of the fibers that strengthen plants.
Sources include all kinds of fruits and vegetables, especially in their peels, and in the husks of grains, and seeds.
Which type of fiber is best?
Most high fiber foods contain a combination of both soluble and insoluble fiber- i.e. a sweet potato has insoluble fiber in its peel, and soluble fiber in its flesh. Preparation method of foods can also influence the type of fiber it contains. For example, potatoes when cooked and warm have insoluble fiber in the peel, soluble fiber in their flesh, and once cooled, develop resistant starch.
We need all types of fiber for waste removal and for the health of our gut microbiome. In a healthy person, all fiber will offer benefits. For those with compromised digestive systems, insoluble fiber can be irritating. They may need to temporarily limit insoluble fibers and other high fiber foods. It’s important to work with a qualified practitioner to strategically use fiber - especially soluble fiber - to restore gut health.
THE TAKEAWAY
Fiber consumption impacts many important body systems including gut, endocrine, brain, immune and metabolic functions.
Aim to include plant foods at every meal to meet optimal amounts of fiber daily. As a general guideline, consume a variety of vegetables (aim for 8 servings/day) and eat fruit in whole-form (2-3 servings/day) as opposed to in juice form, which strips away fiber.
Consume a variety of nuts, seeds, legumes, and root vegetables. Their soluble fiber helps feed the microbes in our gut, which is key for gut health, and lowering inflammation. Plus, they help clear excess hormones and produce compounds that impact our brain and mood.
Pro Tip (especially for women, and especially those who struggle with excess estrogen, PMS, PCOS, migraines, endometriosis, etc): consume 1-2 tablespoons of seeds like ground flax and/or chia everyday.If you have gut issues like IBS, IBD, leaky gut, dysbiosis, SIBO etc. high fiber foods can aggravate your symptoms, especially insoluble fiber. You might need to temporarily limit these by peeling fruits and vegetables, and temporarily avoid the ones that give you symptoms. However, because soluble fiber is key food for the microbiota, which in turn affect inflammation levels, and immune, brain, endocrine and metabolic health, it’s important to work with a health practitioner to strategize how to heal the gut lining before adding more fiber to your diet.
High fiber foods help stabilize blood sugar, consume fiber with every meal, including snacks, to keep blood sugar steady.
REFERENCESParladore Silva, Y., Bernardi, A. & Luiz Frozza, R. (2020). “The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication.” Frontiers in Endocrinology.
McManus, K.D.(2019). “Should I be eating more fiber?” Harvard Health.
Kajla, P., Sharma, A., Sood, D.R. (2015). “Flaxseed: A Potential Functional Food Source.” Journal of Food Science and Technology.
Romm, A (2nd edition, 2017) Botanical Medicine for Women’s Health. pp. 255-256
Herbalmedicineforwomen.com
Kresserinstitute.com