As if excess salt, fat and several types of sugar weren’t bad enough, the ingredient lists of much ultra-processed food often end with a befuddling number of additives. Either written as E numbers or given their full chemical names, this information is unsettlingly opaque to non-experts, prompting many of us to just refer to them derogatively as “chemicals”, even though, technically, everything is made of chemicals.

One category of these additives – emulsifiers – has hovered below the radar for many years. But as scientific understanding of the gut microbiome has grown, they have emerged as potential culprits in the modern western diet’s attack on gut health. And, as we now understand, gut health means general health because it governs everything from mood and metabolism to inflammation and immune response.

But emulsifiers are hard to avoid. “In the UK, there are 63 different types in the food supply,” says Kevin Whelan, head of nutritional science at King’s College London. “We’ve done a research study showing that more than 6,000 foods in the UK contain emulsifiers.” Some foods contain multiple emulsifiers, “three, sometimes four and up to 11”.

This is because emulsifiers are extremely useful. “They can be used for bread, chocolate, cakes, ice-cream, margarine and processed meats,” says food scientist Natalie Alibrandi, founder and CEO of Nali Consulting. They help products stay smooth and uniform in texture, and stop ingredients separating. “An emulsifier is used to combine water and oil,” says Alibrandi. “It is structured with a hydrophobic side, which does not like water, and a hydrophilic side, which does like water. So one side is helping bind to the oil or the fat in the product, and the other side is helping bind to the water.”

The ingredients list for Kingsmill’s Mighty White bread includes emulsifiers E471 (Mono- and diglycerides of fatty acids), E472e (diacetyl tartaric acid ester of mono- and diglycerides or DATEM) and E481, (sodium stearoyl lactylate or SSL). For bread, cakes and pastries, says Alibrandi, as well as helping keep the product consistent wherever it’s made, “they can help increase the shelf life, and make it softer, with less drying effects”. But particularly in baked goods with different components, from sponge and fillings to icings and chocolate drops on top, the various emulsifiers in the product can soon add up.

Emulsifiers are used in chocolate to delay the appearance of a white bloom that can happen if the sugar or fat rise to the surface. “With ice-cream,” says Alibrandi, “it’s so important to have the right amount of fat and air to create the ice structure [texture]. By adding an emulsifier, you’re helping combine the fat and water to create that structure. The same would go for margarine.”

Some brands, she says, are eschewing additives, with slogans like “separation is natural”. She gives the example of certain plant-based milk products. The downside for the consumer, she says, “is that when they add their non-dairy milk to their coffee, it separates. It doesn’t look good, it doesn’t taste good, it’s got a different texture. Whereas by adding emulsifiers, you can help make the product look and taste smooth.”

Alibrandi is comfortable eating them, noting that they’ve been used for more than 50 years in the industry and have long been deemed safe by the appropriate bodies. “Emulsifiers are ubiquitous,” she says. “They are in everything within the food and beverage industry, and we wouldn’t have the convenience and shelf life of products that we do without having these types of ingredients.”

The trouble is, says Megan Rossi, research fellow at King’s College London and founder of The Gut Health Clinic, that the original food safety assessments were done before we knew much about the gut microbiome. She, and the other researchers who have turned their spotlight on emulsifiers, are primarily trying to help those with inflammatory bowel disease – incidences of which have steadily increased since food became industrialised. It is now rising in economically developing countries. “We’ve known for a long time that people who eat a more ultra-processed diet seem to be at higher risk,” says Rossi, “which we’ve been trying to get our heads around for decades. Inflammatory bowel disease affects one in 200 people. So it’s really quite common and there’s not really a cure for it at the moment.”

There are many elements in an ultra-processed diet that could play havoc with the gut microbiome, but in terms of emulsifiers, says Rossi, “if you think about how they combine water and oil together and turn into this kind of soap [emulsifiers are also used in detergents], we think that may make the gut lining more vulnerable to penetration of specific inflammatory microorganisms”.

Preliminary research has indicated this could well be the case, and it is this research that is now grabbing headlines. It began in earnest in 2015, says Whelan, when a paper was published by one of their collaborators, Benoit Chassaing at Université Paris Cité. He tested the effects in mice of two common emulsifiers: CMC (carboxymethyl cellulose), and P80 (polysorbate 80). “He fed them water containing either CMC, P80 or neither,” says Whelan, “and he found that the mice consuming the emulsifiers had dramatic changes to the diversity of their bacteria. They had a reduction in the number of different types of bacteria in the gut. We don’t think that is a good thing to happen to your gut microbiome.” Greater numbers of pro-inflammatory bacteria were present, too, but this wasn’t all.

In the mice that consumed emulsifiers, the mucus wall that protects their guts was much thinner. “The emulsifiers had emulsified the mucus, so some of it had been dissolved away,” says Whelan. “This meant the bacteria were much closer to the lining of the gut. What he also showed was that there was much more ‘leaky gut’ – the passage of bacteria, but also other molecules getting through the lining, causing more inflammation.” It looked as though these emulsifiers could be driving inflammatory disorders of the gut such as Crohn’s disease and ulcerative colitis. But these were mice, not humans.

The next step was to eradicate emulsifiers from people’s diets, and see if this helped ease their inflammatory conditions. This is where Whelan came in. “I spend all my time designing diets that are complex, and trying to work out how we might be able to get people to follow them,” he says.

His team started with a small feasibility study in 2020, in 20 people with Crohn’s disease, to see if they could manage to avoid emulsifiers for two weeks. “We found that compliance was really good,” says Whelan, “and actually, lots of people felt a little bit better. The problem is, you can’t take that as proof that the diet works, because when anybody gets a lot of support, and takes part in a study, they feel a little bit better.” That’s why the big trial they are currently undertaking includes a control group on a placebo.

Meanwhile, US researchers in 2017 had run another small study in which 12 patients with ulcerative colitis, the long-term inflammation of the colon and rectum, cut all emulsifiers from their diets for up to 12 months. Five took a daily capsule containing the emulsifier carrageenan, and the other seven participants took a placebo capsule. Three of the five taking carrageenan relapsed, while none of the placebo group did. The same year, the European Food Safety Authority identified food emulsifiers as an emerging risk.

Whelan’s new clinical trial is placebo-controlled, with 150 people with Crohn’s disease. For eight weeks, half will consume a normal diet, and half will move to a low-emulsifiers diet, to see if that will make their inflammation better. “We’re about two-thirds of the way through,” he says, “and we’re really excited to get more patients, so if you can mention that in the article that would be amazing for us.”

This work-in-progress situation leaves consumers in a tricky situation – should we be searching the back of every food packet for emulsifiers before buying? “I can understand that lots of people are concerned about what to eat,” says Whelan. “But my view is it’s too early to be saying we should not be adding emulsifiers to our foods. I also think it’s too early to be saying that everybody should stop eating any emulsifiers in foods.” But that doesn’t mean people shouldn’t start trying to eat a less processed diet. “We should be encouraging people to cook more from scratch, not rely so much on packaged ready meals and things like that – there’s certainly no harm in doing that.”

Among the many things we don’t know about emulsifiers is which, if any, are the most harmful. After his early mouse studies, Chassaing experimented with many more emulsifiers. “Some really didn’t have any effect at all,” says Whelan. “Soy lecithin [commonly used in chocolate] has not very much of an effect. But again, this is only in animals. Nutrition is so nuanced, so now is not the time to start advising people on which ones to avoid.” Eventually, when robust work is complete, there may be scope to work with the food industry to help them reformulate. “There are lots of opportunities and it’s a complex problem to solve.”

Complex indeed. Sarah Berry, chief scientist at Zoe, a personalised nutrition app based on research by gut health scientists, says that emulsifiers, in her opinion, “are only a fraction of the problem with ultra-processed foods, and I think where we go wrong is over-focusing on single ingredients”. It’s not that she doesn’t think emulsifiers aren’t a potential problem, but they’re just one of many ways in which ultra-processed foods affect health. They are more calorie-dense than minimally processed equivalents and we consume them 50% faster, she says, which means our fullness signals don’t have time to kick in. Normally, it would take “about 10 to 20 minutes” to feel full, Berry adds.

Ultra-processed foods tend to have less of the healthy ingredients such as fibre, high-quality proteins and healthy fats. And they tend to pack in more sugar and saturated fat. Added to all this is one of Berry’s recent research topics, which is how the structure of food is changed by industrial processing. She has found that products using commercially ground almonds are 30% more calorific than whole almonds, and eating powdered porridge oats results in a 30% higher sugar spike, simply because more cell walls have been broken, releasing more calories.

And when it comes to the additives, emulsifiers aren’t the only ones in question. There are also stabilisers, preservatives, colourants and sweeteners – all contributing, says Berry, “to this perfect storm”.

This isn’t about scaremongering: scientists are loth to trigger premature conclusions about individual ingredients, although in Rossi’s own clinical practice, she says, “when I’m talking to clients, or patients, I do say that we are investigating food additives that, if you have a predisposition, or if you do have Crohn’s disease, that it probably is smarter to try to limit the amount of these ultra-processed foods, many of which contain these food additives.”

Rossi says she understands why so many people struggle to kick the habit of consuming processed foods, despite their health impact. “I’m a busy mum,” she says, “and packaged foods – let’s face it – allow us to function, to work full-time and all that sort of stuff.” While she is conscious of how many different types of additives are in the foods she chooses, she advises we remember that they’re not all evil – and ill effects are dose dependent. Lecithin is a type of emulsifier, she says, but is found naturally in eggs. “So I think we need to be cautious of how obsessive people get with food additives – another common additive is ascorbic acid, which is vitamin C. We shouldn’t be demonising all additives, and a lot of them do ensure there’s a longer shelf life.”

Not all ultra-processed foods even contain emulsifiers, or any harmful additives, but will have some of the other unhealthy attributes that Berry listed. “We have probably been too reliant on these ultra-processed foods,” says Rossi. “We need to dig a little bit deeper into what we’re consuming. Certainly it’s not going to be toxic or cause cancer overnight, so we can still include them. But if most of your diet is coming from these ultra-processed packaged foods, then it probably is worth re-evaluating.”