Can food preservatives affect gut bacteria?
Gut flora on (and not on) the intestines.

Can food preservatives affect gut bacteria?

Over a week ago, I bought some nan breads from Costco and they were delicious. We had half a packet that evening which meant there were still 6 left over. Today I ate the last one for lunch and it was 9 days old, yet it was still soft, white and unblemished with mould. I wonder how long it would have stayed good for? It got me thinking about why there was no bacteria and mould growing on it. Are the preservatives so toxic that they just won’t grow there? Can food preservatives affect my gut bacteria?

Why is gut bacteria important?

Gut bacteria are so useful, they help our digestion by breaking down our foods and also keep us healthy by fighting off bad bacteria and improving our immune systems and moods. The things we eat are in turn consumed by them, and the better the diet, the stronger and more diverse the microbiome is. It stands to reason that we need to nurture our inner communities for our mutual benefit.

Homemade vs Shop-bought

I make most of my food from scratch, but not everything: that wouldn’t be possible unless I wanted to cook all day long. Some things like bread, I make when I have time but buy ready-made the rest of the time. Homemade never lasts long; within a day, it’s getting hard and within about 3 days, the first spots of mould start appearing. It’s the same with so many homemade foods. When you start to compare homemade to shop-bought, it’s astonishing how much longer the factory-made ones last. Of course, preservatives have their place in keeping things safe for consumption, but am I the only one who is freaked out by tortilla wraps which last for weeks, or mayonnaise that lasts for months? Someone once said to me ‘consider why a cream-based drink like Baileys can stay fresh for years without refrigeration’.

Killing bacteria

It makes sense to think that if bacteria and moulds in the environment don’t thrive on processed food, then our gut bacteria won’t be able to make use of them either. Surely eating a lot of preservatives will actually starve or even kill the good bacteria inside us? Here’s a link to an in-vitro study published in 2017 which shows that 4 species of common human gut bacteria are adversely affected by sulphites. The study was not conducted in-vivo, but is there any reason to think that the results would be different in or out of the body?

The above photograph shows the ingredients of the bread I ate today. The first preservative is E202, or potassium sorbate which kills yeast and bacteria. E282 or calcium propionate, which is a fungicide and mould inhibitor.


Government guidelines allow factories to use preservatives so we all think they are safe to consume, but no one knows how much is safe over the course of a day, month or year. Also, what about the combined toxic load of different preservatives? Things that most of us eat on a daily basis, like bread, mean that we are continually ingesting anti-bacterials, yet many of us are also spending time and money trying to eat more probiotics! A packed lunch may contain something seemingly harmless like a mustard and ham sandwich, but if we stop to think about it, the ham is full of nitrates which prevent the growth of bacteria and both the bread and mustard contain a variety of preservatives.

Everyone knows that processed food is full of bad fats, salt, sugar and preservatives yet we all consume them and most of us eat them every day in the form of cereals, baked foods, preserved meats, condiments and confectionery. Apart from causing obesity, I believe one of the dangers is the constant assault on our helpful bacteria. Millions of us have bloating, constipation, digestive problems and immune disorders. Could your daily sandwich or afternoon snack be to blame? It’s food for thought!

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Charlin has a background in teaching and education but has always had a keen interest in health, nutrition and spiritual wellbeing. She lives in Surrey with her cycling obsessed husband and three crazy children. She works as a reiki master/teacher at and writes for

Let me know what you think, please leave a comment!