🥝 Fiber is NOT Essential! (I mean it)

Having read that first line you might be wondering if I’ve had a stroke.

The fiber evangelist himself denying the truths of fiber?! It’s not even April 1st!!

Technically, fiber isn’t “essential” for human survival. You could go your whole life without it and… well… you’d still be alive.

But “alive” isn’t the same as thriving.

That’s why I still make sure I get a consistent, measured dose of fermentable fiber every single day.

Your gut bacteria aren’t one big, uniform blob all happily munching the same thing. They’re a bustling metropolis of hundreds of species, each with their own favourite fuel sources…and when you don’t give them fiber, the whole city changes its economy.

Some are saccharolytic, meaning they thrive on fermenting complex carbohydrates and fibers into beneficial compounds like short-chain fatty acids (SCFAs). Butyrate, propionate, acetate; these are the real stars of gut health, feeding your gut lining, calming inflammation, and keeping your immune system balanced.

Others are proteolytic, meaning they prefer to ferment proteins. Sounds fine in theory, but when this becomes their main gig (usually because they’ve run out of fiber to eat), the byproducts are… not exactly health-promoting…

Things like:

• Ammonia; irritating to the gut lining.
  

• Phenols & p-cresol; linked to DNA damage and oxidative stress.
  

• Hydrogen sulfide; the stinky stuff yes…in small amounts it’s fine, but too much can impair mitochondrial function and epithelial health.
  

• Lipopolysaccharides (LPS); components of bacterial cell walls that, when they leak into the bloodstream, can trigger immune activation and systemic inflammation.
  

This shift from saccharolytic to proteolytic fermentation isn’t instant but it happens surprisingly quickly when fiber disappears from the menu. Studies show that within 1–3 days of a low-fiber diet, microbial metabolism can change, leading to lower SCFA production and higher levels of these potentially harmful metabolites.

And yes fiber is technically not “essential” in the same way vitamin C is. You can survive without it.

But there’s a difference between surviving and thriving.

Without fiber, your microbes do what they have to do to stay alive…but in the process, you end up with fewer protective compounds, more inflammatory byproducts, and a gut barrier that’s just that little bit more vulnerable. Over time, this can look like:

• Increased intestinal permeability (“leaky gut”)
  

• Higher baseline inflammation
  

• Impaired metabolic health
  

• Disrupted gut–brain signalling (yes, this can influence mood and cognition)
  

Now, in an ideal world, we’d all be eating 30–40g+ of diverse fiber daily from a rainbow of whole foods…legumes, fruits, vegetables, whole grains, nuts, seeds. That’s what keeps your gut bugs in their preferred saccharolytic mode.

But in reality, 95% of adults in the UK and US don’t even hit the minimum recommended 25–30g/day. And even those who do often get it from the same few sources, which means they’re feeding the same handful of microbes on repeat while others go hungry.

This is why I aim for two things:

1. Consistent quantity; enough grams of fermentable fiber daily to keep SCFA production high.
   

2. Diversity; multiple types of fiber so I’m feeding the full microbial team, not just the star players.
   

Because if you leave your microbes hungry for fiber, they’ll happily switch to protein fermentation. And while they’ll survive…you might not love the trade-off in the long run.

Think of it like this: your gut bacteria are employees. Feed them well, and they’ll work hard to protect you. Starve them of fiber, and they’ll still show up to work…but now they’re burning the furniture to stay warm.

And p.s, your gut lining is that furniture.

Oh I have some very very exciting news to share with you next week (I hope)...no, no-one is pregnant…so simmer down folks! It’s still very cool though, so keep an eye on my socials!

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