How Food Preservatives Can Disrupt Our Gut Microbiome

Sam Westreich, PhD

These additives could contribute to throwing our guts out of whack — or even making us sick
"Yes, it's preserved... but is it good for me?"Photo by Micah Tindell on Unsplash
Shelf stability is a great thing, these days. We’re able to keep food for a much longer time, able to enjoy a wide variety of flavors and components at almost any time of the year. Aren’t you glad that your bread doesn’t mold after a few days, that your candy bars are perfectly tasty even after weeks in the cupboard, that your soda always tastes the same and never has bacteria in it despite being chock-full of the sugar they love?

These days, many different foods contain various preservatives, helping to keep them shelf-stable. These preservatives can include sulfites, nitrites, sodium benzoate, sorbates, bromates, and various natural chemicals that also have a preservation aspect.
Tons of foods contain preservatives, not just these.Source: Perfect Keto

We generally know that foods loaded with preservatives aren’t great for us. (For one thing, those foods tend to not be as naturally high in vitamins, minerals, and fiber that we need. What’s healthier for you — an apple, or a glass of apple juice?)

But these days, when we think about health, we can’t be so selfish as to only focus on ourselves. What about the trillions of tiny little passengers that we carry around with us, that are dependent on what we eat in order to get their own nutrition?

I’m speaking of the gut microbiome, the collection of many different species of bacteria living inside your lower intestinal tract. This little rainforest of many different bacterial species, all living in a balance of cooperation and competition, lives as a passenger in our bodies — but its composition has effects on our own health.

Our microbiome impacts how we digest food and what nutrients we absorb from it, but its effects don’t stop there. It helps to train our immune system, teaching our immune cells what is dangerous and what is nonthreatening. It can contribute to our weight gain and loss, and the wrong microbes seem to promote obesity. It even produces neurotransmitters and hormones that can impact our mood and mental health. Even if you don’t like cats and dogs, you’ve got to care for your microbes.

So what about food preservatives? What do they do for our gut microbiome?

Look at mice, because ethics boards aren’t that cool with feeding people nothing but ice cream

First off, we need to understand the main method by which the impact of these chemicals on the gut microbiome is studied: it’s usually in mice.

Why mice? There are a few advantages:

  • Mice are usually on controlled diets, so we can know exactly what foods go into them. Mice won’t sneak off to the kitchen late at night to cheat on their diet with a box of Oreos!
  • It is generally more acceptable to feed an extreme diet to a mouse that may cause lasting damage to its microbiome and health, than it is to do to a human.
  • We can create a “humanized” gut microbiome in a mouse by feeding it antibiotics to kill its natural microbes, and then giving it a fecal transplant from a human.

So what happens when we give mice a diet that contains high levels of food preservatives? Does their gut microbiome respond?

It does — and not in a good way.

Some mice were given high levels of emulsifiers, food additives that help stabilize mixtures; we get them in foods like mayonnaise, creamy shelf-stable pasta sauces, baked products, peanut butter, and ice cream. These mice saw an overgrowth in mucus-degrading bacteria, which led to colitis, where the bowel became inflamed.

A similar effect happened when the mice were given high levels of maltodextrin, a thickener that’s added to lots of processed food, like instant pudding, gelatin, sauces, and salad dressings. In this case, the maltodextrin impaired our goblet cells, cells in the intestinal lining that produce protective mucus.

The end result was the same — colitis, inflammation as the bacteria broke through that mucus barrier, sneaking out of their intestinal tract home and invading the rest of the body.

Another study fed a combination of preservatives — sodium benzoate, sodium nitrite, and potassium sorbate — to similar mice with human gut microbiomes. (Sodium benzoate is commonly in sodas, sodium nitrite is used to preserve meats and cheeses, and potassium sorbate is commonly found in baked goods, in both the cakes and the icing.)

These additives are designed to be antimicrobial; that’s a good thing in food, but a bad thing in our guts, where we want to keep our delicate balance of microbes that best suits our health. In the study where the mice consumed these antimicrobials, levels of Clostridiales dropped, while levels of Proteobacteria rose. Even at levels that are considered safe for human consumption (and inclusion in our food), our microbes are affected by the preservatives in the food we eat.

And these studies were not giving massive amounts of preservatives — they showed that, even at concentrations that are considered safe in food, there’s an impact on our microbiome.

In a meta-analysis, a compiled table shows how a wide range of different food preservatives were noted in various animal models to have a range of negative effects, many linked with gut microbiome imbalances. The most common negative effects were dysbiosis (disruption of the normal makeup of the microbiome) and increased inflammation (swelling, pain, increased immune system activity) in the gut.

How are these issues not seen in the population? It may be, some researchers suggest, because we each have a slightly different, unique gut microbiome composition. You don’t have the same balance of bacteria that I do — and mine may be more vulnerable to preservative agents than yours is.

What can we do?

This is really the million-dollar question. We know that preservatives aren’t great for us, and that they can cause dysbiosis and inflammation in the unlucky individuals who have gut microbiomes especially susceptible to these additives.

But can you even avoid additives? It’s going to be tougher than it may seem at first glance. Emulsifiers are used widely, and many of them are considered “natural”, so they can still be present in foods labeled as organic, or foods that claim to be free of any artificial agents.

But overall, it is possible to reduce and aim to minimize the amount of consumed processed food. These agents aren’t used to preserve raw ingredients, like fruits, vegetables, and some basic grains (although they are present in dried fruits and in many baked goods, like white bread).

Even some “natural” preservatives can still pose a risk. One popular tactic for makers of preserved meats is to use celery powder instead of adding sodium nitrate. The package of hot dogs or bacon will proudly proclaim that it is “free of any added nitrates”.

But celery powder is a naturally occurring, rich source of nitrates. A number of studies agree that it’s no better than adding sodium nitrate directly.

The ideal answer is to add preserved meats to the list of items to avoid. Get your hot dogs straight from the local butcher, with no preservatives added, and eat them quickly as an occasional treat, one not meant to be saved. If you want cookies or a cake, bake it yourself from raw ingredients.
No! Bad! Do not eat! Preservatives!Photo by James Day on Unsplash

But it’s not an answer that’s going to work for everyone. Many of us love our junk food, even when we know that it’s not great for us. And if putting some emulsifier-laden salad dressing on our meal helps us to eat more vegetables, doesn’t that balance out?

In the end, like many factors that impact the gut microbiome, the best choice is probably moderation, working towards as much healthy, long-term reduction as possible. We can’t expect everyone to give up processed goods, immediately and forever.

But we can ask for people to try and make healthier choices when possible, limit the overall amount of processed foods, and try to provide time for a damaged gut microbiome to regrow — especially if someone knows that their microbiome is vulnerable to the damaging effects of food preservatives.

In summary: natural or artificial, preservatives fight off microbes — in our food and in our body both

Preservatives are great discoveries for shelf-stable food, especially when that food is highly processed and would otherwise be vulnerable to bacterial growth. Preservatives keep our sodas crisp, our salad dressings thick and creamy, our baked goods fresh, our cookies and crackers from spoiling, our dried fruits from rotting, our processed meats tasting salty and flavorful on or off the grill.

But those same preservative ingredients have been demonstrated to have negative effects on our gut microbiome. The level of effect varies from person to person, since some microbiome makeups are uniquely vulnerable to the damaging effects of preservatives.

In the worst cases, they can degrade the protective mucosal lining on the inside of our intestine, allowing microbes to cross over into the rest of our body and set off inflammation. They also more strongly reduce some species of microbes, compared to others, throwing our biome out of balance.

There’s no easy solution, other than reduction and avoidance. Perhaps someday, we’ll each keep a healthy sample of our own individual microbiome on hand, so we can always restore back to a healthy level — but for now, we need to protect our microbiome by being careful what we feed to it.

After all, for most of us, the microbiome we’ve currently got is our only option.

Do you try to avoid preservatives, either natural, artificial, or both, in your food? Do you find that you feel negative gut effects if you eat foods high in preservatives?


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A microbiome scientist working at a tech startup in Silicon Valley, Sam Westreich provides insights into science and technology, exploring the strangest areas of biology, science, and biotechnology.

Mountain View, CA

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