Let's Talk Fiber

What is fiber?

Found primarily in fruits, vegetables, nuts, seeds, and whole grains, fiber is a complex carbohydrate and can be classified as soluble or insoluble. There are many forms of soluble fibers (pectin, guar and xantham gum, psyllium), with a compelling bulk of research supporting claims of improved digestion and gastric emptying, improved blood sugar response (particularly in prediabetic and diabetic individuals), lower LDL cholesterol, and even decreased inflammation and improved immune function. Insoluble fibers (like inulin and cellulose) contribute to our GI health by adding bulk to stool and aiding with constipation by acting as a “scrubbing agent” within the digestive tract. Both soluble and insoluble fibers increase our satiety (fullness), making them powerful tools for individuals looking to drop a few pounds.

While insoluble fibers do not, soluble fiber dissolves in water and acts as fermentable “fertilizer” for the bacteria hanging out in our gut, allowing the thousands of species of microorganisms in our gut to flourish. This is where the term prebiotics come into play, as all forms of over the counter prebiotics are different forms of soluble fibers. Including sources of prebiotic fiber in our diet and diversifying the ecosystem within our gut microbiome has very strong links to the prevention of various diseases including colon cancer, inflammatory bowel disease and irritable bowel syndrome, cardiovascular disease and type 2 diabetes.

Prebiotics are not to be confused with probiotics, which are microorganisms including bacterias and yeasts present in fermented dairy like yogurt or kefir, fermented vegetables like pickles or sauerkraut, over the counter supplements, or your favorite bottle of Kombucha. If prebiotics are considered the “food,” then probiotics are the microorganisms that consume the food. Consuming probiotics will be particularly helpful to diversify and repopulate the microbiome after sickness or antibiotic use, while prebiotics will “keep the fire going.”

How important is fiber really?

Ok, so you've heard fiber is good for you, but how good? In a meta analysis posted by Reynolds et. al. (2020), all cause mortality risk and cardiovascular risk was reduced by up to 35% by simply increasing daily fiber intake from 19 grams per day to 35 grams per day. This was observed amongst nearly 2,000 participants with type 1 or type 2 diabetes over the course of 8 years. Not only that, but there were statistically significant reductions in Hemoglobin A1C, fasting blood glucose, insulin resistance, LDL cholesterol and total cholesterol. Longer duration cohort studies comprising 980,000 participants highlight a strong inverse association between fiber and all-cause mortality, and it was concluded by Yang-Yang et. al. (2015) that there is a 10% reduction in risk for every 10 additional grams of fiber consumed per day. Yafei et. al. (2025) demonstrated that for every 5 additional grams consumed per day, there was a 7% reduction in all cause mortality amongst post-menopausal women.

While there is some research indicating a reduced risk of breast cancer with fiber consumption, there is a convincing amount of data supporting the significant impact fiber has on colorectal cancer. Song et. al. (2018) investigated 1575 participants with stages I–III colorectal cancer and observed an 18% and 14% reduction in colorectal related mortality and all cause mortality, respectively.

So how important is consuming adequate fiber? In short, regular fiber consumption has the potential to have a greater impact on your long-term health than:

• Your favorite supplement
• The type of protein you eat
• Whether you eat organic
• Intermittent fasting

Are there any downsides?

Certain camps within the wellness community will make the argument that consuming foods with fiber puts you at risk due to the high amount of oxalates, phytic acid, or other “defense chemicals,” due to their ability to reduce absorption of specific micronutrients, or else the nutrients are bound up in the fiber. While there are some practices that most can adopt like soaking nuts, seeds, or grains to improve digestibility, these claims are largely misrepresenting the take home points. In short, the dose makes the poison.

For example, phytic acid (present in oatmeal) can bind to iron, calcium, or zinc, removing our ability to absorb as much of said nutrients. However, phytic acid is also an antioxidant and is associated with reduced cancer risk. Red meat contains formaldehyde, apple seeds contain cyanide, and water is toxic in high quantities. It is the dose of these compounds that dictate the effect they have on our health. We cannot isolate one compound and allow that to dictate safety of consumption. Rather, we observe the larger body of research measuring outcomes and corresponding disease risk.

So are there any downsides to fiber? Short answer, no. This does not mean jumping from 10 grams to 65 grams within a day. Much like exercise, a steady exposure over time will reduce chances of unwanted symptoms like constipation, mild GI distress, bloating or cramping.

Where can I get it?

The Dietary Guidelines for Americans recommends 22–34 grams per day depending on age and sex, while the National Academy of Medicine recommends roughly 14 grams of fiber per 1,000 calories consumed. Therefore, an individual consuming north of 2,500 calories should expect to aim for 35+ grams of fiber per day.

Something as simple as adding ¼ ounce of chia seeds and ½ cup of raspberries to your microwave oatmeal will provide a nutrient dense, filling meal with over 10 grams of fiber. Intentional between-meal snacks like oranges or apples, mixed nuts, or a handful of berries can help boost daily numbers consistently.

When in doubt, combine nutrient and fiber rich foods with foods you already like. Add tomatoes, broccoli, bell peppers and/or onion to your eggs, or else supplement your homemade enchilada recipe with a fiber-rich, whole grain tortilla. Sprinkle some nutritional yeast on your movie popcorn, or add some granola or blueberries to your morning cereal or yogurt. Maybe even have a few fiber gummies when you're sharing a pint of Ben and Jerry's with your partner.