World Vegan Day: vegan diets & our gut microbes

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By The Gut Health Doctor Team

Dr Megan Rossi in a lab looking through a microscope

Google Trends shows interest in veganism has grown sevenfold over the past 5 years, alongside the number of people following a vegan diet quadrupling. You’ll know by now I’m on a mission to help everyone increase the plant-based diversity in all of our diets – so how does veganism (aka 100% plant-based) influence your gut health?

A 2021 study (Losno et al.) has investigated the effects of vegan diet on our gut microbiota (GM) – here’s what the researchers found.

Spoiler: not all scientific studies have a big result. This month, I wanted to share this study that didn’t have a “ground-breaking” finding – to show you the side of science no-one talks about! We need to look beyond the clickbait headlines and ‘good’ vs ‘bad’ labels when it comes to our nutrition. Sometimes, ‘it depends’ is the best answer.


The study

Researchers pooled together the results of 9 studies that looked at the types of microbes found in the guts of those following a vegan diet for at least 4 weeks, compared to those who ate meat and other animal products (aka omnivores). All the studies were done with healthy adults.


The findings

There were conflicting results, albeit there did seem to be some differences in certain gut microbes among people following vegan diets versus those who didn’t.

  • While one study reported lower GM diversity in omnivorses, two others reported no difference in diversity between vegans and omnivores
  • Most studies showed higher levels of Prevotella in vegans versus omnivores
  • Some studies showed lower levels of Bifidobacteria (health-promoting) in vegans


Full disclosure

I’m all about assessing the quality of new research studies when I share them with you guys, so there are a few things to note. (That’s another reason it’s so important to only take advice from those who are qualified, it can be all too easy to misinterpret the science!)

  • The studies included were also observational studies, so it’s not possible to say whether these differences observed in gut bacteria were definitely down to their diets, or whether there were other important factors at play e.g. sleep, exercise, stress levels
  • The sample sizes were small, with participant groups ranging from 9 – 51 people.
  • The studies’ criteria varied in how long the participants had been following their diets – some had been following the diets for as little as four weeks, others more than a year.
  • What’s more, as the studies assessed participants’ GM using a poop sample, we are at risk of misinterpreting the results. For example, Prevotella can be both beneficial and detrimental, it depends on how we treat them as to how they behave in our gut. Also there’s still so much we don’t know about our gut microbes (we haven’t even named thousands of them!). We simply can’t fully explore the diversity of microbes in a single sample – not yet anyway.


So what does that mean for you?

Well, as I always say, it’s clear our nutrition isn’t black and white – it’s not about whether it’s “good” or “bad”. It’s way more complex than that 😉

Eating more plants as part of a vegan diet could be positive for your gut, and overall, health, thanks to the essential fibre in all of our plant-based foods that nourishes our GM, as well as vitamins and plant chemicals (like polyphenols).

But vegan diets can hugely differ and a ‘vegan’ label doesn’t necessarily mean it’s healthier. A vegan diet that focuses on whole plant foods full of fibre can be beneficial, albeit requiring appropriate supplementation to make sure you’re getting enough of other nutrients our gut microbes love, such as omega 3. In turn, a vegan diet that’s mostly made up of highly processed ‘vegan’ alternatives and white grains isn’t going to do your gut microbes much good.


My advice

Do what feels right for you personally. The body of evidence suggests that we could all benefit from eating more plants – but that doesn’t necessarily have to mean only plants. It really is about finding what works for you and that is what my new book Eat More, Live Well is all about! 

If you are following a vegan diet, it’s a good idea to check the labels of ‘meat-free’ alternatives for any mysterious ingredients!



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