Gut Microbiome

 The gut microbiome primarily feeds on:

🧬 Fermentable Fiber and Resistant Starch — not fat or protein directly.

But let’s break it down clearly:

🌿 What the Microbiome Actually "Eats":

The colon (large intestine) is home to trillions of bacteria.

These bacteria ferment carbohydrates, especially:

Soluble fiber

Resistant starch

Oligosaccharides (like inulin, FOS)

Through this fermentation, bacteria produce:

Short-chain fatty acids (SCFAs) like butyrate, propionate, and acetate.

Butyrate is especially critical—it’s the primary fuel for colonocytes (cells lining the colon).

🥩 Carnivore Diet and the Microbiome:

When you eat only animal products:

There's little to no fermentable fiber, so...

SCFA production drops, especially butyrate.

However:

Some bacteria can switch to fermenting protein, producing different byproducts like:

Ammonia

Phenols

Indoles

These are not as beneficial as SCFAs, and in excess, may be toxic or inflammatory.

🧈 What About Fat?

Fat is absorbed high in the small intestine, so gut bacteria rarely touch it.

That said, a high-fat diet changes the gut environment:

Shifts microbiome composition (often reducing diversity).

Increases bile acids, which certain microbes can use.

Some microbes thrive in fat-rich environments, but not by eating fat directly.

🧠 TL;DR:

Macronutrient Do Gut Bacteria "Eat" It? Key Notes

Carbs (fiber, RS) ✅ Yes – fermented into SCFAs Preferred fuel source

Protein ⚠️ Partially – when fiber is low Leads to toxic metabolites if excessive

Fat ❌ Not really Alters environment, not a food source

On Carnivore:

Your microbiome adapts, but diversity may drop.

Less fermentation = fewer SCFAs, but inflammation may still fall due to absence of irritants.

Still, long-term health of the microbiome on carnivore is not fully understood yet.