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As a personal trainer and someone who did their grad thesis on the microbiota and nutrition, I cannot endorse fiber enough, in any form. Dietary fiber has numerous benefits. It promotes a healthy microbiome, which plays an important part in gut health, immune function, and so much more. 

An easy way to increase your fiber intake is to take prebiotics. One of the best prebiotics you can find is Bulletproof InnerFuel Prebiotic. In this Bulletproof InnerFuel Prebiotic review, we’ll get to know prebiotics, their role in health and physical fitness, and how the supplement stacks up to others. 

Medical disclaimer: This article is intended for educational and informational purposes only. It is not intended as a substitute for medical advice. For health advice, contact a licensed healthcare provider. GGR also recommends choosing a product that has been third-party tested for quality.

Garage Gym Reviews Knows Gut Health

From the best fiber supplements to greens powders for pregnancy, Garage Gym Reviews knows gut health. Our expert testers and reviewers include registered dietitians, Olympic weightlifters, and certified personal trainers. They all take fitness and health seriously. When it comes to supplements, GGR experts have extensive experience, and they’re happy to share their thoughts in reviews such as this.

For this review, our tester was former GGR senior staff writer Amanda Capritto, CPT, CNC. She rated Bulletproof InnerFuel using our supplement testing methodology, which ranks supplements across multiple categories, such as:

  • Formulation. Products with quality ingredients and minimal artificial sweeteners earn higher scores here.
  • Solubility. If a product dissolves well in your favorite beverage, it will get higher marks from our product testers.
  • Taste. While taste is subjective, it’s also an important factor to consider in a supplement. The better the taste, the higher the score.
  • Third-party testing. We prefer brands that have embraced transparency and offer third-party testing of their supplements.

Bulletproof InnerFuel Prebiotic

Bulletproof Innerfuel Prebiotic

GGR Score: 3.38 starstarstarstarstar

Product Highlights

  • Daily prebiotic supplement powder 
  • 17 grams of prebiotics 
  • Bulletproof listed benefits: Eases digestion, feeds good gut bacteria, and supports immune system

Pros & Cons


  • Subscribe and save 20%
  • 100% satisfaction guaranteed - 30 day money-back window
  • Keto-friendly
  • Gluten-, sugar-, and soy-free
  • Non-GMO
  • Positive customer reviews


  • 1 serving is 2 scoops
  • May cause bloating—recommended start with smaller teaspoon serving to assess tolerance
  • Mixed reviews on mixability
  • Processed in a facility that also processes allergens: milk, fish, crustacean shellfish, tree nuts, wheat, and soybeans
  • One container is not a month supply, only “about 20 servings”

Bottom Line

Bulletproof’s Innerfuel Prebiotic is a powder supplement with 17 grams of prebiotics per 2-scoop serving. This supplement is intended to ease digestion, feed and increase good gut bacteria, and support your immune system. Customer reviews of this product are mostly positive and users feel their digestion improved and their stomach discomfort decreased. Some customers noted that the powder did not mix well.

A Quick Look at Bulletproof InnerFuel Prebiotic

Bulletproof started as a simple idea: a coffee infused with MCT oil and grass-fed butter. This novel bulletproof coffee inspired a new approach to mind and body wellness and spawned Bulletproof the brand.

In addition to Bulletproof coffee, the brand now offers a range of supplements that promote immune support and digestive health. These include prebiotic powders; keto-friendly, non-GMO collagen bars; vitamin A+D+K gummies; and greens powders for plant-based health.

RELATED: Bulletproof Collagen Peptides Review

When it comes to prebiotic fibers, there are some things to keep in mind. A research study from 20101 defines a prebiotic as any food product that is fermented by intestinal bacteria and therefore promotes the growth of gut bacteria. Prebiotics consist of soluble and insoluble starches found in most fruits and vegetables, as well as whole grains and fermented foods.

Holding a scoop of Bulletproof InnerFuel Prebiotic in front of the container.

Conversely, probiotics are simply live cultures of bacteria, like those in yogurt, that support a healthy digestive system.2

Prebiotics are the fuel needed to sustain and grow a healthy microbiome, particularly the so-called good gut bacteria3. Our diet heavily influences our microbiome. A healthy gut microbiota is associated with numerous health benefits, including improved immune responses, weight loss, and decreased risk of anxiety, cancer, and diabetes4.

Bulletproof InnerFuel Prebiotic powder is a no-nonsense, non-GMO, and keto-friendly way to dramatically increase your fiber intake and boost gut health. 

Before You Buy

  • Bulletproof InnerFuel Prebiotic contains 16 grams of prebiotic dietary fiber.
  • This product is unflavored, so it will mix well with all your favorite beverages.
  • The 10 grams of organic acacia fiber can help ease digestion.
  • There are 7.5 grams of guar gum fiber to help curb cravings and fuel good gut bacteria.

Is Bulletproof InnerFuel Prebiotic Worth It?

Bulletproof InnerFuel is a solid dietary fiber supplement. With 16 grams of fiber per serving, it’s a great choice for anyone looking to increase their fiber intake. However, at $2.00 per serving, it’s not the most budget-friendly supplement.

bulletproof fiber

Great for:

  • Anyone looking for a simple, high-fiber supplement
  • Folks who value transparency and third-party testing
  • Anyone following a keto or gluten-free diet

Not recommended for:

  • Those who want a complete prebiotic fiber with greens and protein
  • People who don’t need higher fiber intakes
  • People who don’t like powders

RELATED: Transparent Labs Prebiotic Greens Review

Bulletproof InnerFuel Prebiotic Specs

Price per serving$2.00
Serving size2 scoops (19 g)
Fiber per serving16 g (0 g net carbs)
Types of fiberOrganic acacia, guar gum (Sunfiber), larch arabinogalactan (Resistaid)
Third-party tested?Yes, but the company is not listed

Experience Using Bulletproof InnerFuel Prebiotic

This prebiotic fiber is simple, with three different fiber sources, including guar fiber and larch arabinogalactan from the larch tree, all of which can slow food’s passage through the digestive system. I’ve personally tried it and find it a good addition to smoothies. 

Pouring a scoop of Bulletproof InnerFuel Prebiotic into a glass jar.

Overall, Amanda was also satisfied with InnerFuel, giving particularly high scores to its taste and solubility. She noted that it’s unflavored and mixes well with any beverage or food; she also didn’t experience any side effects after following the dosing suggestions on the container. 

What pulled the scores down were the high price and the lack of advertised third-party testing. Let’s see what else she had to say.

Price Per Serving

At $2.00 per serving, InnerFuel earned only 1 star. It’s more than double the price of many other fiber supplements. However, it offers a LOT of fiber per serving, so if you have the budget available and really need to increase your fiber intake, you may find the cost worth it. Bulletproof.com does offer a subscribe & save option, which drops the regular price to $1.60 per serving.


Amanda gave InnerFuel 3 out of 5 stars for formulation. It contains no sugars, sugar alcohols, or artificial ingredients, but it consists of only soluble fiber and has no insoluble fiber. Soluble fiber and insoluble fiber are both important components of our diets, but they come from different sources and have varying impacts on gut health5.

Supplement Facts label on a container of Bulletproof InnerFuel Prebiotic.

RELATED: Best Prebiotic Foods

Taste and Solubility

For taste and solubility, InnerFuel received a perfect 5 out of 5. It’s unflavored and has no noticeable smell. “I was able to mix it into juice, coffee, and protein smoothies without altering the flavor of the beverage,” Amanda noted.

A glass of freshly-mixed Bulletproof InnerFuel Prebiotic.

InnerFuel also dissolves well, with a slightly grainy texture. “This is kind of a grainy/chunky powder. Some of it is really powdery, while some of it is more like sand, but soluble. When I mixed it with anything other than plain water, I didn’t notice any off-putting textures. I didn’t have any issues swallowing it,” Amanda said.

RELATED: Best Fiber Supplements for Constipation

Side Effects

InnerFuel received a 5 out of 5 for side effects—though it is important to follow their dosing instructions. Bulletproof recommends gradually increasing the dose from 1 to 2 scoops. Amanda didn’t do this, instead starting with a full serving on her first dose. “I definitely noticed some bloating an hour after I took two scoops and was uncomfortable for a few hours. I lowered the dose the next time I tried it and had no side effects,” she reported.

Third-Party Testing 

The Bulletproof.com site claims their supplements are third-party tested. However, this information isn’t apparent on the InnerFuel container. We value companies that showcase transparency and prioritize accessibility, so we expect to see validated third-party claims. For this reason, InnerFuel earned only a 2 out of 5. 

Bulletproof InnerFuel Prebiotic vs Metamucil

Metamucil 4-in-1 Fiber

Metamucil 4-in-1 Fiber

GGR Score: 4.5 starstarstarstarstar

Product Highlights

  • Powder psyllium husk fiber supplement 
  • Promotes digestive health and regularity
  • Orange flavor 
  • Subscribe & Save option available
  • Sugar-free blend

Pros & Cons


  • Promotes healthy blood sugar levels
  • No added sugar
  • No.1 doctor recommended fiber, according to Metamucil
  • Gluten-free


  • Metamucil claims are based on small studies
  • Contains aspartame
  • Only 1 flavor

Bottom Line

Metamucil is a plant-based fiber supplement with good reviews for taste and effectiveness.

Metamucil is one of the most common fiber supplements, as it’s available in nearly every grocery store and drugstore. Unlike the unflavored Bulletproof InnerFuel, Metamucil is orange-flavored and isn’t quite as versatile. And while InnerFuel contains no added sugars or artificial ingredients, Metamucil contains artificial flavors, aspartame, and Yellow 6.

Metamucil’s main fiber source is psyllium seed husk, which isn’t as soluble as acacia, one of the primary types of fiber in InnerFuel. But where Metamucil beats InnerFuel is in the price. At less than $0.40 per serving, Metamucil is the better choice for those on a strict budget. 

Bulletproof InnerFuel PrebioticMetamucil 4-in-1 Psyllium Fiber Supplement
Price per serving$2.00$0.17 or $0.37
Serving size2 scoops (19 g)1-2 teaspoons
Fiber per serving16 g (17 g net carbs)3 g or 6 g
Types of fiberOrganic acacia, guar gum (Sunfiber), larch arabinogalactan (Resistaid)Psyllium seed husk
Third-party tested?Yes, but the company is not listedNo

Customer Experience 

Bulletproof offers a range of products and subscribe and save options. You can also frequently find Bulletproof coupon codes. The site boasts a host of claimed health benefits, options for every budget and health goal, and tons of reviews.

Ordering Bulletproof InnerFuel Prebiotic

The ordering process at Bulletproof.com is relatively simple: Go straight to or search for what you want, select the size, select a subscription if you like, and go to the checkout page to complete your order. Bulletproof offers a 30-day return policy for unused products, and has generous options for changing and canceling subscriptions.

A container of Bulletproof InnerFuel Prebiotic is all alone on a lonely countertop.

Customer Reviews

We liked Bulletproof InnerFuel, but don’t take our word for it. There are over 1,700 reviews on Amazon, with an average rating of 4.5 Most of the reviews address how well it mixes, its lack of flavor, and their perceived benefits from the fiber. A few negative reviews mentioned poor mixing, while some customers experienced stomach issues even with small doses. Others were suspicious of the alleged benefits to the digestive system and immune system.

Final Verdict of Our Bulletproof InnerFuel Prebiotic Review

Bulletproof InnerFuel is a decent, high-fiber prebiotic. It earns top marks for formulation, with over 16 grams of fiber, as well as taste and solubility. At $2.00 per serving, it’s one of the more expensive supplements you can try. That said, if you can fit it into your budget, it’s worth a shot. 

Individuals who consume little to no fiber should gradually increase their fiber intake, especially with a supplement like InnerFuel. Otherwise, you may experience bloating and gas. That passes (haha!) relatively quickly, and the fiber will help keep you full.

Here are a few other things you should know:

  • Each serving provides 16 grams of multiple sources of fiber.
  • InnerFuel is keto-friendly and gluten-free.
  • Subscribe & save and multiple shipping options allow flexibility.
  • The high price and lack of insoluble fiber may leave customers wanting a different product.

If you’re interested in a more comprehensive fiber supplement, check out our breakdown on greens powders vs multivitamins.

Full Rating

Bulletproof InnerFuel Prebiotic

Bulletproof’s Innerfuel Prebiotic is a powder supplement with 17 grams of prebiotics per 2-scoop serving. This supplement is intended to ease digestion, feed and increase good gut bacteria, and support your immune system. Customer reviews of this product are mostly positive and users feel their digestion improved and their stomach discomfort decreased. Some customers noted that the powder did not mix well.

Product Currency: $

Product Price: 39.95

Product In-Stock: InStock

Editor's Rating:

Bulletproof InnerFuel Prebiotic Rating

Price per serving – 1
Formulation – 3
Taste – 5
Solubility – 5
Side effects – 5
Third-party testing – 2
Customer service – 5
Customer reviews – 4.5
Buy Now

Bulletproof InnerFuel Prebiotic: FAQs

What is InnerFuel Prebiotic?

InnerFuel Prebiotic is a fiber supplement that helps to feed gut bacteria and promote overall gut health. It contains multiple sources of fiber to help preferentially feed specific bacteria and ease the passage of food through the digestive system.

What is the most effective prebiotic?

The most effective prebiotics will usually contain a mixture of fermentable polysaccharides (complex sugars) such as galactooligosaccharides, fructooligosaccharides, chicory root, and inulin.

What is the difference between a probiotic and a prebiotic?

A prebiotic is basically undigestible plant matter that gut bacteria break down as fuel. Probiotics are live cultures of bacteria found in foods like yogurt. Probiotics often can’t make it past the harsh environment of the stomach and may not have much effect on gut health.

Are prebiotic supplements effective?

Yes. There is countless research that shows the positive impacts of fiber and prebiotic supplements on digestive and gut health, as well as blood sugar control, weight loss, and even immune function.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any diseases.


  1. Gibson GR, Scott KP, Rastall RA, et al. Dietary prebiotics: current status and new definition. Food Sci Technol Bull. 2010;7(1):1-19. doi:https://doi.org/10.1616/1476-2137.15880
  2. Hill C, Guarner F, Reid G, et al. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 2014;11(8):506-514. doi:https://doi.org/10.1038/nrgastro.2014.66
  3. Michael I McBurney, Cindy Davis, Claire M Fraser, et al. Establishing What Constitutes a Healthy Human Gut Microbiome: State of the Science, Regulatory Considerations, and Future Directions. The Journal of Nutrition. 2019;149(11):1882-1895. doi:https://doi.org/10.1093/jn/nxz154
  4. Afzaal Muhammad, Saeed Farhan, Shah Yasir Abbas, et al. Human gut microbiota in health and disease: Unveiling the relationship. Frontiers in Microbiology. 2013;22. doi:https://doi.org/10.3389/fmicb.2022.999001
  5. Mudgil, D. (2017). The interaction between insoluble and soluble fiber. In Elsevier eBooks (pp. 35–59). https://doi.org/10.1016/b978-0-12-805130-6.00003-3

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