Popular diets may help drop pounds, but could negatively impact gut health

Low-carb diets like keto and paleo may be among the most popular choices for New Year’s dieters, yet this type of approach may not be the best for your gut, suggests a new study published in the American Journal of Clinical Nutrition.

In a first-of-its-kind study, researchers found that, out of five eating patterns, individuals following an exclusion diet that was low in carbohydrates and consisting of mainly fats, animal products and non-starchy vegetables had the lowest amount of Bifidobacterium, a type of bacteria shown to have beneficial qualities for their gut microbiome. In addition, individuals following a flexitarian diet, which is rich in plant-based foods but also includes meat and dairy products, presented one of the most diverse gut microbiomes, especially compared to a standard American diet.

The international research team led by Aurelie Cotillard and Patrick Veiga at Danone Nutricia Research in France examined the dietary patterns of 1800 adults in the American Gut Project, an ongoing research initiative that is studying the microbiome composition of citizen volunteers. The project was performed in collaboration with researchers at the University of California San Diego (UC San Diego), whose contributions were coordinated by the Center for Microbiome Innovation at UC San Diego.

Using food consumption surveys, the researchers divided the study participants into five groups based on their long-term dietary intakes:

• Plant-based: Primarily vegetarians and vegans who consumed little or no meat and high amounts of fruits, vegetables and whole grains. This diet was highest in fiber compared to the other four dietary patterns.
• Flexitarian: Individuals who ate abundant amounts of plant-based foods, yet still incorporated some meat and high amounts of dairy foods.
• Health-conscious American diet: A dietary pattern that was rich in nuts, whole-grain cereals, and dairy foods, but was also high in sugary sweets and refined grains, and low in vegetables.
• Standard American diet: These individuals had the poorest diet quality of all groups, including the highest consumption of sugar-sweetened beverages and processed foods and the lowest diversity in plant-based foods consumed, as well as the lowest intake of dietary fiber.
• Exclusion diet: This restrictive diet was the lowest in carbohydrates and highest in fats and animal products compared to all other patterns. It included virtually no starchy foods or sweet products.

The analysis of the gut microbiome of the study participants revealed that the alpha diversity of the gut microbiota (a measure of the different kinds of bacteria), was significantly lower in the standard American diet compared to the flexitarian pattern, which included a mix of plant and animal foods, including high amounts of dairy products. In addition, the low-carb eaters from the exclusion diet had the lowest relative abundance of Bifidobacterium, a beneficial type of bacteria found in the gut. Altogether, this highlights that some diets may be more microbiota-friendly than others. 

In this study, the researchers also found that the overall diet exhibited better associations with the gut microbiome than individual dietary components, such as fiber or protein alone. “The association between a habitual diet and the gut microbiota is gaining major interest, yet, to the best of our knowledge, this is the first study to use this type of approach and identify the dietary patterns providing the best associations with the gut microbiome,” said the senior author of the study Patrick Veiga, Ph.D., Health and Microbiome Science Director at Danone Nutricia Research.

“This study showed that the flexitarian eating pattern that includes larger amounts of plant foods, yet doesn’t totally eliminate animal foods, was associated with better overall diet quality and one of the approaches resulting in the most nourished gut,” said Miguel Freitas, Ph.D., Vice President of Health and Scientific Affairs at Danone North America.  “This study together with previous research reinforce that a healthy gut microbiota is supported by a balance between all food groups, without restricting fiber-rich grain foods or animal products, like fermented dairy products entirely.  At Danone, this approach is completely in line with our portfolio offerings of both plant-based and animal products.”

The study also found that the gut microbiota alpha-diversity of the plant-based diet and the standard American diet was similar, which may be explained by the depletion of some animal foods, such as meat and dairy products in the plant-based dietary pattern. While the intake and diversity of fruits and vegetables have been reported as main factors associated with variations of the gut microbiota, animal protein has also been shown to increase microbial diversity.

“People may overlook that, what they eat and what they avoid, can impact their gut microbiome,” Freitas said.  “Diet is known to influence the diversity and composition of our gut microbiome, which we now know has a tremendous impact on our overall health.”

“These results confirm that evaluating diet as a whole is important when studying the gut microbiome,” said Veiga.  “It will also facilitate the design of more personalized dietary strategies in general populations.”

The study was funded by Danone Nutricia Research and supported by The Microsetta Initiative, the world’s largest citizen science microbiome project.

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*Source: Cotillard A, Cartier-Meheust A, Litwin NS et al.  A posteriori dietary patterns better explain variations of the gut microbiome than individual markers in the American Gut Project. American Journal of Clinical Nutrition. 2021:00:1-12.

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