Fibers, Microbiome, and Inflammation: Understanding Your Gut Terrain

What if fibers were feeding exactly what your body is trying to eliminate?

by Laurent Glatz – for Athletic Carnivore

You’ve been told over and over that fibers are the foundation of a healthy gut. More vegetables, more whole grains, more fermentable fibers, and your microbiome would produce butyrate, repair your mucosa, and calm your inflammation. Yet, for you, it doesn’t work. You add fibers, and your belly bloats. You persist, and fatigue sets in. You continue, and your joints inflame, or your mood collapses for no apparent reason. The problem isn’t your will to eat healthily. The problem might be that with these fibers, you’re feeding bacteria that should never dominate your gut.

The common belief is simple: fibers fuel the good bacteria. But this logic assumes your microbiome is already mostly populated by beneficial fermenters. If your terrain is dysbiotic, if pro-inflammatory species have already taken over, fermentable fibers don’t produce butyrate. They produce endotoxins, gases, and an inflammatory load that crosses the intestinal barrier. Studies published in eBioMedicine by The Lancet show that major depression is systematically accompanied by an enrichment of pro-inflammatory bacteria and a depletion of anti-inflammatory species like Faecalibacterium or Coprococcus.

The same observation appears in osteoarthritis, where bacterial signatures dominated by Proteobacteria and Actinobacteria are found in cartilage and synovial fluid, associated with low-grade joint inflammation.

The central mechanism is not a vague theory. It’s called lipopolysaccharide, or LPS. It’s not an external poison. It’s a molecule that makes up the cell wall of Gram-negative bacteria, notably Proteobacteria such as Escherichia, Klebsiella, or Shigella. When these bacteria proliferate and the intestinal mucosa is weakened, LPS passes into the bloodstream. This is known as "leaky gut." Once in the blood, LPS triggers a systemic immune response: interleukins, TNF-alpha, IL-6. These cytokines cross the blood-brain barrier and activate microglia, creating neuroinflammation directly involved in the pathogenesis of depression.

In depressed patients, increased circulating bacterial DNA and anti-LPS antibodies are indeed measured.

The gut-joint connection follows the same path. Low-grade inflammation initiated in the digestive tract does not remain local. It migrates. Bacterial derivatives reach joint tissues and amplify an already present degenerative or inflammatory process. Arthritic cartilage is not sterile: it contains microbial imprints dominated by Proteobacteria, and this cycle fuels chronic joint inflammation.

In other words, your microbiome doesn’t just cause bloating. It can fuel, via the bloodstream, distant inflammation that settles in the brain and joints.

So, what happens when you increase fibers? In a balanced gut, fermentable fibers are broken down by beneficial Firmicutes into short-chain fatty acids, including butyrate, which strengthens the intestinal barrier and soothes inflammation. In a dysbiotic gut dominated by Proteobacteria, these same fibers become the substrate for pathological fermentation. LPS-producing bacteria multiply, the intestinal wall weakens further, and systemic inflammatory load increases. It’s not the fiber’s fault. It’s the terrain that misreads it.

This is precisely why two people can react oppositely to the same increase in vegetables or grains. One recovers energy and loses bloating. The other sees symptoms worsen, mood decline, and joints stiffen. The difference isn’t the amount of fiber consumed. It’s the microbiome composition receiving it.

Hence the carnivore question, or more broadly, the absence of fiber. If pro-inflammatory bacteria depend on fermentable substrates to proliferate, removing these substrates deprives them of their main fuel. Experimental data show that animal protein intake, compared to soy, reduces LPS-binding protein in serum, a marker of inflammatory reaction induced by intestinal endotoxins.

This doesn’t mean the carnivore diet is a universal solution. It means that removing fibers can act as a diagnostic tool: if your joint inflammation, mild chronic depression, or intestinal fatigue lessen without fermentable substrates, you learn something about your terrain. You learn that your body wasn’t lacking fibers. It was suffering from a dysbiosis that fibers were feeding.

The cost of staying in the dark is real. Continuing to force fibers because it’s "recommended," while your body signals increasing inflammation, risks feeding the wrong fire. It’s not dramatic short-term, but it’s a systematically inappropriate adjustment. Every bowl of vegetables, every portion of whole grains becomes, in this context, reinforcement for bacteria producing the LPS that reaches your brain and joints. The real risk isn’t fiber deficiency. The real risk is correcting the wrong parameter while the terrain deteriorates.

At this point, the question is no longer whether fibers are good or bad in themselves. The question is understanding which microbiome receives them and what it does with them. If your body transforms fibers into butyrate and energy, the direction is clear. If your body transforms them into endotoxins and cytokines, the direction is different. But you can’t guess this by reading general advice. You can only know by reading your own terrain.

Are you nourishing your gut, or are you feeding a dysbiosis you haven’t yet identified?

Analyze my intestinal and metabolic terrain

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