Life in each of us
Microbes & Me is a new collaborative series between BBC Future and BBC Good Food.
In this series, we will examine recent research on the microbiome of bacteria that lives in all of us.
We will study how it affects our health, what its adverse effects would be, and recommend recipes that could help it thrive.
About 10 years ago, Neil Potts, co-founder of the vegan restaurant The Vurger Co, was working long hours in a stressful job when he was starting to have a stomach ache.
They came every few weeks and lasted about 12 hours each for the next five years, but the tests found nothing but a "slightly inflamed stomach."
Then Potts went on vacation to Los Angeles for a few weeks and ended up eating healthier. He did not have much meat or dairy either, which had already been a big part of his diet. His stomach pains disappeared and, upon his return to the UK, Potts embarked on a vegan diet, avoiding all foods of animal origin, including meat, fish, eggs, dairy products and honey.
"In addition to the pain in my stomach that was dissipating, I also noticed a huge difference in my overall fitness," says Potts during the first few months of his vegan spell.
"I never felt better, I had more energy and better skin, and I could not attribute these changes to anything else. And I'm really not a type of miracle healer.
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Potts says the trip made him understand how much the food we eat can affect our guts. Of course, not everyone is intolerant to meat or dairy products, but most of us have felt the effects of our diet on our overall well-being.
But our diet does not just affect our guts the way we can feel it, as was the case with Potts. It is becoming increasingly evident that it can also affect the structure and functioning of our microbiota, the trillions of bacteria living in our intestines, which can also affect our health. And some studies have shown that the vegan diet is the healthiest.
The vegan diet is generally classified as being low in protein, calcium, saturated fat and salt. Since vegetarians have a more limited diet, it is generally assumed that their diet is richer in dietary fiber, found in foods such as legumes, vegetables, nuts, seeds, fruits and grains, than in omnivorous diet.
These foods are undoubtedly some of the healthiest we can eat – and the consensus is that, in general, foods that are well established and good for our health in general would also be best for our microbiomes . But the effects of a vegan diet on our guts are not so simple.
Danilo Ercolini, professor of microbiology at the University of Naples, conducted a study that revealed that most vegans and vegetarians, but only 30% of omnivores, had a diet comparable to the Mediterranean diet. It is a diet rich in legumes, fruits and vegetables, exclusively based on extra virgin olive oil and low in cheese and sugar.
An anti-inflammatory activity in the intestine can help prevent the onset and development of certain diseases.
He found that closely following the Mediterranean diet was linked to higher rates of short chain fatty acids in a person's feces. These molecules are generally considered important for the health of the colon and the rest of the body.
In later research, Ercoloni discovered that polyphenols, the micronutrients found in some plant-based foods, are also useful for intestinal health and have anti-inflammatory properties.
Many health problems, including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and obesity, are related to inflammation, Ercolini explains. An anti-inflammatory activity in the intestine can help prevent the onset and development of certain diseases.
Luca Cocolin, professor of agricultural microbiology at the University of Turin, Italy, discovered in his research that vegetarians and vegans have a set of metabolic pathways, which are reactions in the cells, responsible for the functioning of the body. Gut that omnivores did not have. .
Omnivores had functions related to the metabolism of meat components, but vegans had functions related to the mobility of microorganisms, including flagellin, which he says could protect against diseases, including cancer.
"I speculate, but a much more plant-based diet could help develop functions that can protect against certain diseases, although I do not yet have data to support this hypothesis," he says.
The vagueness of veganism
Some researchers argue that it is misleading to assume that the vegan diet is still predominantly herbal.
Ricci Antonia, scientific director of the Istituto Zooprofilattico Sperimentale delle Venezi, an Italian organization specializing in animal health, recently analyzed the bowels of long-time vegans and found no difference between them and the people with a non-vegan diet.
Ercolini says the vegan diet is not necessarily the healthiest
Antonia recruited more than 100 healthy people, including a third vegetarian, a third vegan and a third omnivore, who asked them to write down what they had eaten for two weeks and to take stool samples from each of them. to examine the diversity of their foods. microbiome community.
She was surprised to find no difference in the number or variety of intestinal bacteria between the three groups. But when she examined the different proportions of nutrients in their diet, she found that all three groups consumed much more than the recommended daily intake of fats and protein and carbohydrates. She says that this is typical for a Western diet, whether it is vegan, vegetarian or omnivorous, and that is probably the reason why their intestinal microbiomes were so similar.
Ercolini says the vegan diet is not necessarily the healthiest. In his study, he also found that many omnivores with a high adherence to the Mediterranean diet consumed less than three servings of animal protein per week. In terms of microbiota and short-chain fatty acids, these omnivores had similar potential benefits for intestinal health compared to vegetarians and vegans whose diet resembled the Mediterranean diet.
"For those who are vegan for health reasons, they should, in my opinion, rethink that because it's never good to be extreme in food choices," he said.
"The more diversified our plans, the better." In this way, you get all the different types of fibers. You can always be an omnivore, eat a lot of vegetables and avoid unhealthy foods such as processed foods, especially those of animal origin. "
In the meat of it
Researchers divide our diet into three categories: vegan, vegetarian and omnivorous. However, while several studies have shown differences in gut between vegan and omnivorous diets, fewer and fewer people have found many differences between vegan and vegetarian diets. One of the reasons may be related to their common exclusion of meat.
A vegan diet can be particularly beneficial if it contains large amounts of dietary fiber
Wendy Dahl, Assistant Professor of Food Science and Human Nutrition at the University of Florida, discovered that a high-protein diet containing red meat was associated with increased production of TMAO , a metabolite associated with heart disease, produced by intestinal microbes and absorbed into the body. Some studies have shown that people who consume a vegan diet have lower rates of TMAO.
According to Dahl, a vegan diet can be particularly beneficial if it contains large amounts of dietary fiber. Dietary fiber is not digestible. Once it reaches the large intestine, it is broken down by a bacterium and the products of this fermentation process can then be absorbed. Fermentation of carbohydrates, a source of fiber, produces short chain fatty acids.
"For people who consume a high-protein, low-fiber diet, the lack of available fiber for bacteria means they ferment everything there, including protein," says Dahl. "It produces other inflammatory compounds. You want to feed the bacterial fiber rather than protein. "
Gary Wu, professor of gastroenterology at the Perelman School of Medicine at the University of Pennsylvania, also found no difference between the microbiota of vegans and that of omnivores, but a greater amount of metabolites in the blood of vegans .
He says that although this may be due to the fact that vegetarians tend to have a more vegetal diet and less likely to develop heart disease, it is not yet clear whether links between health and microbiota intestinal are a cause and effect.
"It's a chicken-and-egg situation," says Cocolin. "Researchers must go from observational studies to correlational studies. It's complicated, but we have to reach a point where we show that some kind of activity in the gut correlates with human health.
If a vegan diet causes changes in the gut, these changes may only last as long as the person is following his diet.
A problem that compares the health of long-time vegans with those on an omnivorous diet is that a large number of vegans choose their diet for health reasons.
This means that they are more likely to adopt other healthy behaviors, such as getting regular exercise and eating more fruits and vegetables, and less likely to smoke and drink. , according to research, and that the intestinal microbiome is also affected by these lifestyle factors.
There is also bad news for omnivores and vegetarians who took part in Veganuary: if a vegan diet causes intestinal changes, these changes could only last as long as the person is following his diet.
Researchers began to study the effect of the vegan diet on bowel health in the 1980s, but veganism was not as popular at the time. It was therefore more difficult to study the effects of a long-term vegan diet. And researchers say it is not yet clear whether adopting a vegan diet can result in intestinal changes similar to those of a long-term vegan diet.
It was found that switching to a vegan diet changed the composition of our guts in less than 24 hours, but these changes could be reversed after only 48 hours of reintroduction of the previous diet.
"Diet is a major component of our gut microbiota, but it further changes intestinal bacteria that determines it," says Cocolin.
"You can change the modulation of the microbiota in a few days, which will affect the functioning and behavior of the microbiota, but when you return to your initial diet, the microbiota returns to its original state," says -he.
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