For most of my life, when I thought of fiber supplements, I thought of older people who were having a hard time maintaining regular bowel movements. I definitely did not expect to be taking fiber supplements myself anytime soon. And yet… I now use a fiber supplement on a daily basis. Let’s talk about why!

what is fiber?

First things first, what is fiber? Fiber is a carbohydrate that human bodies are unable to break down into simple sugars. The body can only absorb carbohydrates that have been broken down into simple sugars, so fiber passes through the digestive tract without ever being absorbed.

There are two kinds of fiber: soluble fiber and insoluble fiber.

Soluble fiber, as the name suggests, dissolves in water. If you’ve ever made chia seed pudding, you’ve noticed how these solid seeds turn into a gel-like substance in water. That’s because they’re high in soluble fiber that dissolves in whatever liquid you’ve soaked them in! Soluble fiber has been associated with better blood sugar management, decreased risk of diabetes, decreased risk of heart disease, and lower blood cholesterol levels.

Good sources of soluble fiber include:

All legumes including beans, lentils, chickpeas, and split peas
Oats
Chia seeds and flaxseeds
Nuts
Apples
Brussels sprouts
Blueberries and raspberries

Insoluble fiber does not dissolve in water. This kind of fiber helps the food you eat to move smoothly through your digestive tract and helps to maintain bowel movement regularity. Insoluble fiber is also associated with decreased risk of type 2 diabetes.

Good sources of insoluble fiber include:

Wheat bran and wheat germ
Oat bran
All legumes
Whole grains
Turnips
Okra
Spinach
Potatoes (both white and sweet potatoes)

Higher consumption of both kinds of fiber combined is associated with lower risks of breast cancer and colorectal cancer.

Within these two categories, there are a variety of kinds of fiber. If nerding on that level of detail is your thing (it’s my thing for sure!), Harvard University has a great discussion on all the different kinds of fiber.

Does the average person get enough fiber?

Whenever I start working with new clients, I ask them to track their food for one week. Then I analyze their diets to find deficiencies. While there has been a lot of variation in how well different clients are doing hitting recommended amounts for most nutrients, across the board, they have been lower on fiber intake, and in particular, soluble fiber intake. The American Heart Association recommends adults consume 25 to 30 grams of fiber per day. Most of my clients started out getting about 15 g of fiber a day, some around 20 g per day, and no one in the 25 - 30 g range. Some sources even recommend consuming 30 to 40 g per day for optimal health.

So… most people have a ways to go to hit that target!

I encourage all my clients to include vegetables at every meal (yes, even breakfast!), which helps get them closer to the target, but sometimes they’re still coming up short.

Which means there might be room to add in supplements.

Let’s see what the literature says on the matter!

Fiber supplementation and PCOS - What does the literature say?

As always, our gold standard for determining the efficacy of any intervention is the randomized control trial, and one has been done for fiber and PCOS! (Although it’s not an ideal study design, which I’ll discuss further below.)

Pourbehi et al. (2020) recruited 54 women with PCOS between the ages of 18 and 45 who were being treated at Urmia Imam Khomeini University Hospital in Iran. The participants were then randomly assigned to either:

Treatment Group: consumed 5 g of psyllium powder dissolved in water 30 minutes before both breakfast and dinner
- Psyllium powder is a commonly used soluble fiber supplement.
Control Group: consumed 5g of microcrystalline cellulose dissolved in water twice per day 30 minutes before both breakfast and dinner
- Microcrystalline cellulose is an insoluble fiber used primarily as a thickening or texturing agent in processed foods.
- Note that while the study considers this group to be the “control” group, ideally, we’d have a control group that was not consuming any fiber supplementation.

The table below includes the changes in a variety of metrics measured by the research team.

While the group taking the insoluble fiber supplement experienced reductions in body weight, BMI, fat mass, and fasting blood sugar, those were the only improvements experienced by this group.

In contrast, the group taking the soluble fiber supplement in the form of psyllium powder experienced reductions in fasting blood sugar, fasting insulin, both measures of insulin resistance, and both total cholesterol and LDL-cholesterol. They also saw an increase in insulin sensitivity. These changes demonstrate significant improvements in metabolic health and cardiovascular health from taking a simple and inexpensive supplement.

Ideally, this study would have had a control group that wasn’t taking any form of fiber supplement, to be able to compare soluble and insoluble fiber supplements to no fiber supplements. However, their study does provide compelling evidence for increasing soluble fiber intake, and this fits with research on the use of pulse-based diets for PCOS.

Summary of changes in biomarkers after 8 weeks of supplementation with psyllium powder, a soluble fiber, or microcrystalline cellulose, an insoluble fiber. “No significant change” means that the team found no statistically significant change for that metric. Results from Pourbehi et al. (2020).

A second study (Cutler et al. 2019) examined correlations between fiber intake and PCOS status, BMI, and degree of insulin resistance. While correlation does not indicate causation, their results warrant discussion here due to the strong associations found.

This study recruited 137 women receiving treatment for fertility challenges at the Grace Fertility and Reproductive Medicine in Vancouver, Canada. 87 of these participants had PCOS while the remaining 50 did not.

From each participant, they obtained detailed records of all food consumed for 2 weekdays and 1 weekend day. They then analyzed nutritional content for each participant, and identified relationships between nutrient consumption and specific metrics of interest.

The first comparison considers nutritional consumption for those with PCOS and those without PCOS. They find that participants with PCOS consumed about 16% less fiber, 22% less vitamin A, 13% less iron, and 19% less magnesium than those without PCOS. The team found no other statistically significant differences in consumption for any other vitamin or mineral considered, for total calories, or for percent of calories coming from carbohydrates, fat, or protein.

The second comparison only considered those with PCOS. For this comparison, the researchers categorized participants by BMI: normal (18.5 to 24.9), overweight (25 to 29.9), or obese (30+). Interestingly, the study team found no statistically significant differences in consumption of any nutritional metric across these three categories of participants. Of note, metrics like total calories consumed and percent of calories from carbohydrates, fat, or protein, did not vary across these three categories.

The last comparison categorized participants by insulin resistance status, using HOMA-IR as their metric, comparing those participants with a HOMA-IR level less than 3.8 to those with a HOMA-IR level of 3.8 or higher. After adjusting for total calories consumed, the researchers found that those participants in the higher insulin resistance category consumed about 16% less fiber than those in the lower insulin resistance category. While this is only a correlation, it does align with the findings found in the study discussed above.

Interestingly, while total calories consumed and percent of calories coming from carbohydrates did not vary across the two categories of insulin resistance, the higher insulin resistance group consumed a glycemic load that was 34% higher than the group with lower insulin resistance. This supports the idea that a lower glycemic load diet is helpful for women with PCOS.

Lastly, this study finds a strong negative correlation between fiber consumption and levels of the androgen hormones testosterone and DHEAS. These hormones are responsible for the acne, excessive facial and body hair, and male pattern baldness experienced by those with PCOS.

Take home points

Supplementation with soluble fiber is associated with improved metabolic and cardiovascular health.

Consumption of both soluble and insoluble fiber is associated with lower incidence of PCOS. It should be noted that PCOS is generally recognized to be genetically predetermined. However, nutrition and lifestyle can mitigate the effects of genetic predisposition to such an extent that individuals no longer meet the diagnostic criteria for PCOS.

Increased consumption of fiber is associated with lower levels of insulin resistance and lower levels of testosterone among those with PCOS.

my favorite soluble fiber supplement

As mentioned in the beginning of this post, I use a fiber supplement every morning. Several months ago, I started adding FiberMend by Thorne to my morning coffee.

[TMI warning - I’m about to talk about my bowel movements!]

Prior to using this supplement, I tended a bit towards chronic diarrhea with the occasional bout of constipation, no matter what I did to support my gut health. After only a few days of using FiberMend, my bowel movements were consistently a 4 on the Bristol Stool Chart. We generally want to remain in the 3 - 5 range on this scale, so consistent 4’s are amazing!

I’ve had a few clients who have also experienced improvements in their regularity from taking this supplement, but I’ve also had a couple who experienced no significant changes. My clients have also used the supplement in conjunction with other nutritional changes, so I cannot speak to the impacts of the supplement alone on measures of insulin resistance.

Like most nutrition and health-related things, experimentation to see what works for YOU is key.

If you’re interested in giving FiberMend a try, you can use the link below to get it through my Fullscript Dispensary, where you’ll always receive 10% off.

Get Fibermend

If supplements aren’t your thing, consider trying to work in more of the high-fiber foods listed above and make sure to get a mix of soluble and insoluble fiber.

References

Cutler DA, Pride SM, Cheung AP. 2019. Low intakes of dietary fiber and magnesium are associated with insulin resistance and hyperandrogenism in polycystic ovary syndrome: A cohort study Food Science & Nutrition, 7:1426–1437. https://doi.org/10.1002/fsn3.977

Pourbehi F, Ayremlou P, Mehdizadeh A, and Zarrin R. 2020. Effect of Psyllium Supplementation on Insulin Resistance and Lipid Profile in Non-diabetic Women With Polycystic Ovary Syndrome: A Randomized Placebo-Controlled Trial. International Journal of Women’s Health and Reproduction Sciences, 8(2):184–191 https://doi.org/10.15296/ijwhr.2020.29