What is already known
A low-fat vegan diet has been associated with health benefits including reduced risk for cardiovascular diseases, whereas high-fat, low-carbohydrate diets — commonly referred to as ketogenic or keto diets — have been linked to reduced brain inflammation. However, how different diets impact the human immune system and microbiota remains unclear.
What this research adds
Researchers assessed changes in the immune system and gut microbiota of 20 people who switched to a vegan and a keto diet. The vegan diet triggered responses linked to innate immunity — the body’s first line of defense against pathogens, whereas the keto diet stimulated responses associated with adaptive immunity — a type of immunity that develops after exposure to a pathogen. Diet switching also changed the participants’ gut microbiotas in ways that modified host metabolism.
Conclusions
The findings show that two weeks of dietary intervention are sufficient to influence host immunity, metabolism and gut microbiota composition. A better understanding of the drivers of microbiota shifts may help modulate gut microbes using dietary interventions.
Nutrition is a critical part of a person’s health, but how it affects the immune system and the gut microbiota remains largely unknown. Now, researchers have found that two weeks of dietary intervention are sufficient to influence host immunity, metabolism and gut microbiota composition.
The findings, published in Nature Medicine, could have implications for precision nutrition. What’s more, a better understanding of the drivers of microbiota shifts may help modulate gut microbes using dietary interventions.
“Nutrition affects all physiological processes, including those that regulate our immune system,” the researchers say. For example, a low-fat vegan diet has been associated with health benefits including reduced risk for cardiovascular diseases, whereas high-fat, low-carbohydrate diets — commonly referred to as ketogenic or keto diets — have been linked to reduced brain inflammation. However, how different diets impact the human immune system and microbiota is unclear.
So, the team — led by Verena Link at the US National Institutes of Health in Bethesda, Maryland — set out to assess changes in the immune system and gut microbiota of 20 people who switched to a vegan and a keto diet.
Divergent immune responses
The participants were split into two groups: one group started on a vegan, low-fat diet for two weeks and then switched to a keto, low-carbohydrate diet, and the other group started with a keto diet and then switched to a vegan diet. The researchers collected blood, urine and stool samples before the dietary interventions and at the end of the first and second diets. Then, they analyzed the samples to assess the body’s metabolic and immune responses, as well as the gut microbiota composition.
The vegan diet triggered responses linked to innate immunity — the body’s first line of defense against pathogens, whereas the keto diet stimulated responses associated with adaptive immunity — a type of immunity that develops after exposure to a pathogen.
In particular, the vegan diet was associated with the upregulation of pathways involved in antiviral responses, while the keto diet was linked to an increase in pathways involved in T cell activation and the number of B cells.
“Our study revealed that a 2-week dietary intervention can impose a striking shift in host immunity, superseding genetics, age, sex, ethnicity, race and even body mass index,” the authors say.
Microbiota shifts
The diet switch also resulted in changes in the participants’ gut microbiotas, the researchers found. Switching to a keto diet resulted in increased levels of Bacteroides sartorii, Bacteroides vulgatus and other bacterial species known to be enriched in animal-rich diets. Changing to a vegan diet led to shifts in the abundance of species associated with fiber- or plant-rich diets such as Bifidobacterium longum and Bifidobacterium pseudocatenulatum.
A keto diet also resulted in the downregulation of many metabolic pathways, including those involved in the production of amino acids and vitamins. “Reduction in amino acid metabolism within the microbiome following ketogenic diet may result from higher abundance of amino acids in the ketogenic diet, making the host less reliant on microbiome-derived amino acids,” the researchers say.
Although both diets influenced host immunity, the keto diet had a broader impact on the gut microbiota and the host metabolism. The reasons behind this effect remain unclear, and more work needs to be done to understand how consuming specific diets may influence disease states, the authors say. “We believe that our present findings further highlight the great potential of highly controlled dietary interventions to better understand integrative physiology, improve human health and mitigate disease.”
