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Diet and lifestyle

Oral bacteria differ between vegans and meat-eaters

Bacteria play a greater role in people’s lives than was previously thought. They do not simply cause serious infections or help us to achieve a healthy gut. New research suggests that oral bacteria can affect our health in the long term.

Your taste buds are not the only things you tickle when you bite a juicy apple or chew a tasty steak. There are millions of oral bacteria; each type has its favourite dish, and those getting the appropriate quantity and quality of food multiply the most. Conversely, other types of bacteria die out when they lack the right food. Oral bacteria do not merely cause cavities in our teeth. They can also strengthen or weaken health in the short and long term and influence the development of periodontitis and possibly such lifestyle-related diseases as heart disease and diabetes.

“We investigated whether the difference in the composition of oral bacteria between vegans and other people may help to explain vegans’ lower prevalence of such lifestyle-related diseases as heart disease and type 2 diabetes. However, we found that a vegan diet actually promotes the bacteria that increase the risk of dental problems and heart disease. The positive impact of a vegan diet must therefore have another explanation,” explains Tue Haldor Hansen, postdoctoral fellow, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen.

Fish or no fish

In the new studies, Danish researchers monitored 160 healthy and fit people. Half were vegans, and half ate both meat and vegetables. Using a special method called 165 rRNA gene sequencing, the researchers identified specific bacteria in saliva samples from both the vegans and the omnivores.

“We searched for the types of bacteria that are known to help to create the inflammatory conditions that increase the risk of heart disease, obesity and diabetes in the long term. We know from previous studies that vegans generally have a lower incidence of these diseases, and we therefore expected the meat-eaters to have more of these types of bacteria. However, we found precisely the opposite, although the difference was not massive.”

The bacteria discovered in the saliva samples were not definitively pathogenic. Nevertheless, the researchers showed that some bacteria that were overrepresented in the mouths of vegans are associated with inflammatory conditions in the body. To determine how a vegan diet changes the composition of bacteria, the researchers more closely examined which substances in the food could make a difference.

“We noticed that the composition of fatty acids in the food differed greatly in the diets. A plant-based diet lacks some of the fatty acids present in fish oil that are associated with protecting people against heart disease and other diseases. Laboratory experiments have previously shown that these fatty acids have an antibiotic-like effect on certain oral bacteria. Our study showed an association for the first time between the fatty acids in fish oil as part of the diet and the composition of oral bacteria.”

No absolute truth

The new study thus indicates in several ways how people’s diet affects the composition of oral bacteria. The study adds to the growing number of studies around the world on how diet affects the bacteria in our gut and mouth. All these studies show that diet clearly determines which bacteria thrive. Nevertheless, Danish researchers believe that it is too early to draw definite conclusions.

“Vegans might want to be aware of this although the difference is not that great but still interesting. However, we emphasize that this was a pilot study to find interesting phenomena that could be examined in greater depth.”

The discovery has mainly stimulated researchers to continue to identify bacteria that live in people’s mouths and that researchers believe may contribute to why some people develop heart disease, diabetes and other diseases.

“Bacteria in our gut influence our health and mental state, and oral bacteria appear to have a similar effect. We have therefore started a larger study of both sick and healthy people. One way we are doing this is through whole-genome sequencing of oral bacteria samples. This will give us a much more detailed picture of the differences in the bacterial flora of people who have heart disease versus healthy people.”

“Impact of a vegan diet on the human salivary microbiota” has been published in Scientific Reports. The Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen conducted the study.

Tue Haldor Hansen
Postdoc
We perform genetic, microbiome and metabolome studies in monogenic diabetes, childhood obesity, Inuit in Greenland and large-scale genetic epidemiology studies. We use national registers to identify families and cases with extreme phenotypes, and have initiated whole exome sequencing and large-scale studies of the oral microbiome in relation to cardiometabolic health and disease. Our major aims are: 1) to define subsets of cases with cardiometabolic disease and define optimal preventive and curative strategies 2) to define health associated genetics and microbiomics 3) to obtain a deeper understanding of cardiometabolic dysfunction at the molecular, organ and whole body level applying deep phenotyping, various imaging technologies and omics profiling methods.