Q&A: Why this microbiologist warns against consuming food dyes

The 1st century Roman gourmet Apicius is said to have coined the phrase “we eat first with our eyes,” and nearly 2,000 years later, that idea still holds true.

However, while some modern foods may be visually appealing, the same food colourings that make them look appealing can potentially create toxic by-products that harm your gut microbiome.

New research from molecular biologist and University of Guelph professor Emma Allen-Varcoe finds that when microbes in our gut try to break down certain food dyes, they form toxic, acidic compounds.

She's with CBC Kitchener-Waterloo. Morning Edition Join host Craig Norris as he discusses where to find these dyes, how to avoid them, and what you need.

This interview has been edited for length and clarity.

Craig Norris: Tell us more about your research and what you found out about food colorings.

Emma Allen Varcoe: I'm a microbiologist and I work on the gut microbiome, and the gut microbiome is an important part of this story, and the reason is that in the past, artificial food colorings, particularly what are called azo dyes, were thought to be pretty inert and not to have much of an effect even if you ingested them in large amounts, and I think that's how they were regulated.

But what we actually found is that when you ingest these dyes, there's nothing any part of your body can do about it. But the microbes that live in your gut are really good at breaking down these dyes. And when they do, they turn them into some not-so-good stuff that's actually toxic to your cells.

CN: What foods contain these dyes?

EA: Well, anything that's bad. And again, I should point out that natural food dyes are a whole other thing. They're mostly harmless, whereas these azo food dyes tend to be used in highly processed foods.

These are found primarily in candy and sports drinks, and the bright, natural-looking colors are probably due to the use of azo dyes.

Azo dyes are also found in cosmetics and medicines, such as those cold medicines and bright red syrups you take when you're sick.

CN: So why are these dyes used?

EA: That's a question I've always been asked. I'm from the UK and these aren't used much in the UK, so when I first came to Canada I was a bit shocked by the colors of the candy and food in general.

The reason for these is a bit confusing to me, but they actually have no nutritional value – they don't add anything to the food in terms of flavor, taste or nutrition, they just add color.

So it's all about aesthetics. The foods that these ingredients are in are the kind of foods that we shouldn't be eating in the first place. I think the reason they're colored that way is to make them look good, especially for kids. That's my big concern.

CN: Who do you think should pay attention to this research?

EA: Three groups of people.

First of all, the general public. We hear all the time about what we should and shouldn't eat, but it's actually relatively easy to look at food packaging and see if it contains azo dyes. A few that come to mind are one called Tartrazine, one called Allura Red.

I think the second group that should really pay attention to this is the food manufacturers themselves, who are probably the hardest to convince because they've been using these kinds of food colorings for so long.

They are very easy to use because they are very chemically stable compounds, meaning that adding them to food, heating, drying, or exposing them to light have no effect on the dyes.

And the third group that I think we should look at is probably Health Canada. They're the agency that regulates the use of dyes in food. They mean well, they monitor how dyes are being used. But they're probably using a lot of information that's based on original studies that gave rats huge amounts of Allura Red or something. We're talking about the '70s, maybe the '60s. They weren't looking at the gut microbiome back then.

CN: So what's next to happen to get regulation of food colorings?

EA: I think this is really a question of awareness. We're just beginning to look at this, but what we know from our research is that the vast numbers of microbes that live in your gut can actually break down these food dyes and make toxic compounds.

I think we need to do more research to understand what these toxic compounds actually do. Everyone's gut flora is different, so they react a little differently to these dyes. That said, since these compounds don't add anything to food other than color, I think it makes sense to eliminate them from your food altogether.

Listen | Emma Allen Varcoe, a molecular biologist and professor at the University of Guelph, says of food colorings: