Fibre myths: microbial diversity

Okay, so I’ve talked fibre and constipation.⁠

How about the notion that plant fibre is prebiotic in nature and thus feeds our gut flora and is therefore essential for microbial diversity?

Well, studies show

• increased dietary plant fibre does not increase microbial diversity[1]
• low fibre ketogenic diets do not decrease microbial diversity[2]

Okay, so what about no plant fibre? Surely we need some?⁠

Nope! According to Michelle Hurn in her book The Dietitian’s Dilemma, evidence from individuals undergoing faecal testing after following a low carbohydrate, ketogenic or carnivore diet show that plant fibre is not needed for a diverse gut microbiome.⁠

So what then feeds the gut flora if we are not eating plant fibre?⁠

Animal foods actually contain a form of fibre.⁠

Two examples of good sources are collagen and cartilage. So, a diet based solely on animal foods can still contain appreciable amounts of prebiotic material, especially a diet that includes different animal parts. Think fish with skin and bones (eg sardines and salmon), chicken wings, and cartilage from the ends of bones.

Humans do not have the gut of a cow or a gorilla! When we eat plant fibre, most of it cannot be broken down. Only a very small amount will be broken down by our gut flora. Eating a large amount of fibre only leads to bloating and gas from its fermentation (see previous post). ⁠

References

1. So D, Whelan K, Rossi M et al. Dietary fiber intervention on gut microbiota composition in healthy adults: a systematic review and meta-analysis. American Journal of Clinical Nutrition. 2018;107(6):965–983.
2. David L, Maurice C, Carmody R et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014;505:559–563.