Why Fiber Isn’t Fuel and What Actually Supports Energy

Fiber is often treated as a nutritional requirement for energy, metabolic health, and gut function, especially within plant-forward dietary frameworks.

But this framing misses a fundamental distinction:

Fiber does not directly fuel the body or brain.

That doesn’t mean fiber has no role. It means fiber is often assigned functions it does not actually perform, particularly when it comes to energy metabolism, brain fuel, and systemic stability.

This distinction matters not only for people with migraines, but also for those eating lower-plant, animal-forward, or ketogenic diets, as well as anyone questioning whether high fiber intake is necessary for human health.

What Actually Fuels the Body and Brain

From a metabolic standpoint, the body runs on:

• Glucose, derived from carbohydrate metabolism
  

• Fats and ketones, derived from fat metabolism
  
  

These fuels:

• Enter cells directly
  

• Produce ATP (cellular energy)
  

• Support organs with high energy demand, including the brain⁵
  
  

This is the body’s primary energy system. Fiber does not participate in this process directly.

Fiber Is Not a Primary Energy Source

Fiber is a carbohydrate that humans cannot digest directly. Unlike glucose, fats, or ketones, fiber does not enter cells to produce ATP. Instead, it reaches the colon largely intact, where it may be fermented by gut bacteria into short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate.¹

These short-chain fatty acids:

• Primarily support colon cells (colonocytes)²
  

• Act as local signaling molecules influencing inflammation and gut integrity³

• Do not function as meaningful fuel for the brain or most tissues⁴
  
  

This distinction is often blurred in nutrition messaging, where fiber is described as if it “powers” the body. In reality, its role is supportive and indirect, not foundational to energy metabolism.

Butyrate: Supportive, Not a Substitute

Butyrate is a short-chain fatty acid that plays a local, supportive role rather than acting as a primary fuel. It helps nourish the cells lining the colon, supports gut barrier integrity, and participates in signaling processes related to inflammation and metabolism.²³⁶

What this means is that butyrate does not power the brain or provide whole-body energy in the way glucose or fats do. Its effects are concentrated in the gut, where it supports structure and regulation, not systemic energy production.⁴

This distinction matters when evaluating whether fiber fermentation is necessary for metabolic health.

Getting Butyrate Without Heavy Fiber Dependence

Importantly, butyrate does not have to come from fiber fermentation alone.

It is present directly in certain animal-based foods, particularly:

• Butter and ghee
  

• Full-fat dairy
  

• Ruminant fats (beef, lamb)⁷
  
  

These foods provide butyrate without relying on bacterial fermentation of fiber⁸.

For people eating animal-forward or lower-plant diets, this helps explain why gut function and metabolic stability can remain intact, even with reduced fiber intake.

What About Ketogenic or Low-Plant Diets?

Fiber is, by definition, plant-derived. But humans do not have a defined biological requirement for fiber itself. 

What the body actually requires:

• Adequate energy
  

• Stable blood sugar
  

• Amino acids
  

• Fats
  

• Minerals and electrolytes
  
  

Ketogenic and animal-forward diets meet energy needs primarily through fats and ketones, reducing reliance on fermentation pathways for metabolic support⁵. Ketogenic approaches require deliberate mineral intake to avoid neurological stress.

In this context, fiber becomes optional support, not a requirement.

Is There Fiber in Animal Foods?

There is no true fiber made from animal protein.

Substances sometimes mislabeled as “animal fiber,” such as:

• Collagen
  

• Gelatin
  

• Glycosaminoglycans
  
  

are structural proteins or compounds, not fermentable carbohydrates. They support connective tissue, not short-chain fatty acid production⁹.

Signs Often Attributed to “Low Fiber”

There is no clinical diagnosis of fiber deficiency.¹⁰

Symptoms often blamed on low fiber, such as constipation or digestive discomfort are more often related to:

• Low fat intake
  

• Inadequate hydration
  

• Electrolyte imbalance
  

• Rapid dietary shifts
  
  

Fiber is one variable among many, not a universal solution.¹¹

If Fiber Isn’t Fuel, What Should You Prioritize Eating?

When energy and stability are the goal, the question isn’t how to maximize fiber, it’s how to consistently meet the body’s primary needs.

1. Protein as the Foundation

Protein provides amino acids required for:

• Neurotransmitter production
  

• Blood sugar stability
  

• Tissue repair and resilience
  
  

Prioritizing protein at meals, especially earlier in the day, helps reduce reliance on rapid glucose swings for energy.

Examples: Beef, lamb, poultry, eggs, fish, shellfish, full-fat dairy (if tolerated)

2. Fats That Provide Direct Energy

Fats are a primary energy source and the raw material for ketone production. Unlike fiber, fats are directly usable fuel.

Examples: Animal fats (tallow, butter, ghee), fatty cuts of meat, full-fat dairy, olive or avocado oil (as tolerated)

3. Mineral-Rich Foods

Many symptoms attributed to “low fiber” are actually related to low minerals, especially sodium, potassium, and magnesium.

Examples: Salted foods to taste, meat and seafood, broths and soups, mineral support when needed

Meeting mineral needs often improves digestion and regularity independently of fiber intake.

The Takeaway

Fiber plays a role in digestion, but it is not fuel.

Human metabolism is powered by glucose and fats, with ketones acting as a critical alternative fuel. Short-chain fatty acids like butyrate can support gut health, whether produced via fermentation or obtained directly from animal fats, but they do not replace the body’s primary energy systems.

For people eating lower-plant or animal-forward diets, the key is not forcing fiber intake, but prioritizing energy, stability, and foundational nutrients first. When those needs are met, digestion and regulation often follow more naturally.

Want to read more like this? Check out this blog:

Beyond Sugar: How the Brain Uses Fat for Energy

Sources

Dietary Fiber and the Gut Microbiota – Cell Host & Microbe
https://www.cell.com/cell-host-microbe/fulltext/S193131281830266X

Utilization of Nutrients by Isolated Epithelial Cells of the Rat Colon – Gastroenterology
https://pubmed.ncbi.nlm.nih.gov/7084619/

Role of Short-Chain Fatty Acids in Host Physiology – Cell
https://pmc.ncbi.nlm.nih.gov/articles/PMC11528394/

Ketone Bodies as a Fuel for the Brain During Glucose Hypometabolism – Frontiers in Nutrition
https://www.frontiersin.org/articles/10.3389/fnut.2021.783659/full

Ketone Bodies: Physiology, Pathophysiology and Application – PMC
https://pmc.ncbi.nlm.nih.gov/articles/PMC7699472/

Butyrate Enhances the Intestinal Barrier – Journal of Nutrition
https://academic.oup.com/jn/article/139/9/1619/4670464

Short-Chain Fatty Acids in Humans – Scandinavian Journal of Gastroenterology
https://pubmed.ncbi.nlm.nih.gov/1994196/

Dietary Fat, Gut Microbiota, and SCFAs – Nutrients
https://www.mdpi.com/2072-6643/10/6/769

Collagen Structure and Stability – Annual Review of Biochemistry
https://www.annualreviews.org/doi/10.1146/annurev.biochem.77.032207.120833

Dietary Reference Intakes: Fiber – Institute of Medicine
https://nap.nationalacademies.org/read/10490/chapter/1

Dietary Fiber and Body Weight – Nutrition
https://pubmed.ncbi.nlm.nih.gov/17379039/