Regular consumption of a common synthetic food dye widely used in sweets, soft drinks, and cereals could be impacting our gut health – and not in a good way.

A new study on mice suggests the colorant Allura Red AC can trigger inflammation of the large intestine if eaten regularly. When consumed by younger mice, it appeared to enhance the risk of developing gut issues later on.

'Regular' in this instance means daily exposure, something that might only apply to hardcore fans of colored candies and vibrant breakfast cereals. What we see in mice also doesn't necessarily translate neatly to humans.

But discoveries like these can tell us a thing or two about interactions between our diet and our gut's biology that warrant further investation.

This isn't the first time scientists have uncovered concerns involving Allura Red (also known as FD&C Red 40 and Food Red 17) either. Along with other organic compound colorants known as azo dyes, the food dye is poorly absorbed in the intestine and can be eaten by microbes in the gut, arguably leading to toxic and possibly carcinogenic effects.

Previous studies have suggested the consumption of food dyes is linked to immune reactions, adverse allergic responses in children, and even behavioral disorders like hyperactivity and attention issues.

These initial findings have led many European nations to strictly control Allura Red's use, if not ban it outright. Products containing synthetic food dyes must now also carry a label warning of potential health effects. In the United States and Canada, on the other hand, the synthetic ingredient can still be used to color foods so long as products list the dyes in their ingredient list.

Today, the use of Allura Red is growing alongside a rising demand for ice creams, candies, gelatine desserts, and other brightly colored food items that tend to feature heavily in Western diets.

Outside of studies investigating Allura Red's potential influence over various behavioral disorders in children, comparatively little research has been done on the ingredient's effects on our gut health, despite emerging evidence raising serious concerns.

"What we have found is striking and alarming, as this common synthetic food dye is a possible dietary trigger for IBDs," says immunologist Waliul Khan from McMaster University in Canada.

"This research is a significant advance in alerting the public on the potential harms of food dyes that we consume daily."

When ingested, Allura Red is metabolized by intestinal bacteria, and previous studies on mice have shown that low doses of the dye can damage DNA in the colon.

To investigate this effect further, Khan and colleagues tested a handful of synthetic colorants, including Brilliant Blue and Sunset Yellow, on human tissues and mice to model their effects on inflammatory bowel diseases (IBDs) like Crohn's and ulcerative colitis.

When lab-grown human intestinal cells were exposed to colorants for 24 hours, researchers found every single one of the dyes had an effect. In the presence of the colorants, human gut cells began secreting more colonic serotonin than they otherwise would have. They also found Allura Red had the biggest effect.

Incidentally, seratonin – a signalling molecule involved in many biological processes – is closely associated with IBD.

Based on the results of the cell experiments, Khan and colleagues proceeded to test Allura Red's effect in mice.

Animals fed a normal diet without food dye for 12 weeks showed no significant changes within their gut, while mice fed a daily dose of Allura Red showed mild inflammation of the colon. Notably, a barrier usually formed by intestinal cells was also impaired.

Serotonin was a key mediator of these changes, appearing to prime cells of the gut to the toxic effects of food colorants.

When mice were bred to lack serotonin transporter proteins, levels of colonic serotonin went up, as did inflammatory markers, leading to greater inflammation.

"This study demonstrates significant harmful effects of Allura Red on gut health and identifies gut serotonin as a critical factor mediating these effects," says Khan.

"These findings have important implications in the prevention and management of gut inflammation."

Further experiments showed that consuming Allura Red daily altered the animals' gut microbiome, which might explain how serotonin could affect the colon, but that remains unclear. Its role in shaping the microbiome is likely to be complex, but given how easily food dyes are gobbled up by resident gut microbes, there's a possibility this dye is wreaking havoc on the system's usual activity.

More research is needed to confirm whether the results are comparable in humans, but given the widespread use of synthetic colorants, it's crucial that scientists figure out how they might impact our gut's health in the long term.

If food colorants like Allura Red really can make children more susceptible to IBD in the long run, it could partly explain why cases of Crohn's and ulcerative colitis are on the rise in older adults.

"This is particularly important since synthetic colorants are a convenient and low-cost alternative for food manufacturers to make foods even brighter and more appealing to the customer, particularly young children," the authors write.

"This study thus will not only prompt scrutiny of its use in many industries but also advance public awareness to prevent adverse health consequences," they conclude.

The study was published in Nature.