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Widely used food additive affects the human gut microbiota
Researchers say it's time for new assessments of additives used in foodstuffs.
Have you heard of E415? It is also commonly referred to as xantham gum, and you are likely consuming it several times a week.
Xanthan gum is used in everyday foods such as baked goods, ice cream and salad dressings. The additive is also widely used as a substitute for gluten in gluten-free foods.
New research now shows that xanthan gum affects our gut microbiota.
Not absorbed during digestion
The study was recently published in Nature Microbiology by a team of scientists at NMBU in collaboration with the University of Michigan and several other international partners.
"We were surprised at how much the human gut bacteria have adapted to this additive since it was introduced into the modern diet only fifty years ago," says NMBU researcher Sabina Leanti La Rosa.
When it was first introduced, xanthan gum was thought to not affect us as it was not digested by the human body.
However, the new study shows that the additive nevertheless affects the bacteria that live in our intestines.
Intestinal bacteria break down E415
Despite previous beliefs, researchers found that bacteria in the intestines have developed to be able to break down xanthan gum. The smaller molecules are fermented into short-chain fatty acids in the gut. These fatty acids are then absorbed by the body and used as energy.
"The gut bacteria we have investigated show genetic changes and a rapid adaptation to enable them to digest this particular additive," explains professor Phil Pope, leader of the Microbial Ecology and Meta-Omics group at NMBU.
A new food chain in the gut
The study shows that the ability to digest xanthan gum is surprisingly common in the industrialised world and appears to depend on the activity of a single bacterium that is a member of the family Ruminococcaceae.
Together with postdoc Matthew Ostrowski and professor Eric C. Martens, both from the University of Michigan, the NMBU-scientists have used several different methods that analyse genes, transcripts, proteins and enzymes produced by the gut bacteria, to uncover how this single bacterial species digests xanthan gum.
The work includes laboratory testing of stool samples from many human donors, mouse experiments and data from large international databases of microbial genes.
“The bacterium that can digest xanthan gum was found among the gut microbiota of surprisingly many people from industrialised countries,” says La Rosa.
In some samples, another type of microbe was also found that interacted with the xanthan gum, this one in the species Bacteroides intestinalis. This bacterium could hijack and further break down small pieces of xanthan gum created during the digestion of the larger xanthan molecules by the Ruminococcaceae bacterium.
The Bacteroides bacterium was equipped with its own special enzymes that allowed it to eat these small xanthan gum fragments.
The study demonstrates the existence of a potential xanthan gum-driven food chain involving at least two types of gut bacteria. It provides an initial framework to understand how widespread consumption of a recently introduced food additive influences the human gut microbiota.
“The most innovative elements of our study are the advanced approaches we combined in order to identify uncharacterised metabolic pathways in microorganisms that are part of a complex microbial community, without the need of isolating each single microbe in monoculture. Then, we characterised in detail the enzyme systems for xanthan gum degradation, to validate our bioinformatics-based predictions. This multi-disciplinary approach provides a blueprint to understanding metabolism within the human gut microbiota and can be applied to any complex gut ecosystem,” explains La Rosa.
“The methodologies used in this study are certainly pushing boundaries and enable us to really deconstruct microbiomes to answer important biological questions that have societal relevance,” says Pope.
Starting to see long-term effects
In Norway, around 300 additives are approved for use in food. Xanthan gum, or E415, is one of these.
The additive is generated by fermenting sugar using the bacterium Xanthomonas campestris. The production process creates a jelly-like liquid that is dried and turned into powder.
Xanthan gum was developed in California in the sixties and was approved as safe for use in food by the U.S. Food Safety Authority in 1968. Today it is commonly used across much of the industrialised world.
"We are now starting to see long-term effects of xanthan gum that were not seen when it was first introduced into the human diet," says La Rosa.
Xanthan gum is a different type of carbohydrate from those that the human body is used to consume, such as starch from plant food. It has a different chemical structure. Xanthan gum is a type of complex carbohydrate that is not similar to any of the plant fibers we normally eat.
Gluten-free and low-carb
Xanthan gum is also used as a substitute for gluten in gluten-free foods and is sold as a separate dietary supplement for keto/low-carb diets.
According to La Rosa, this is because experts have concluded that the substance is not digested by the body, and thus should not be counted as part of the calorie intake.
However, she explains that they now see that the intestinal bacteria break down xanthan gum into smaller molecules. These are fermented in the intestine and then produce short-chain fatty acids which are absorbed into the body as nutrients. Short-chain fatty acids are known to supply up to 10 per cent of calories to humans.
"The new information therefore indicates that xanthan gum should actually count as part of the calorie intake," she says.
The impact on our health
"Based on this study, we cannot conclude if and how xanthan gum affects our health. But we can say that the additive affects the microbiota in the gut of people who consume it through food," says La Rosa.
A large part of the population in the industrialised world have a low, but constant consumption of xanthan gum. Specific subgroups, such as those with gluten intolerance, may have a higher intake. This highlights the need to better understand the effects of xanthan gum on the ecology of the human gut microbiota and on overall host health.
"We only see these changes in gut bacteria of people eating a 'westernised diet' where processed foods and additives make up a significant part of the food intake. For example, we do not see the same changes in indigenous people from different parts of the globe who eat limited amounts of processed foods," La Rosa says.
La Rosa believes that authorities should take this new information into consideration when evaluating commonly used food additives, especially now that it is clear that they do in fact impact our microbiota.
Ostrowski et al. Mechanistic insights into consumption of the food additive xanthan gum by the human gut microbiota. Nature Microbiology, 2022. Doi.org/10.1038/s41564-022-01093-0
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