Beginning a Vegan or Ketogenic Diet Quickly Changes the Immune System

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New findings from the National Institutes of Health (NIH) researchers showed that people who switched to a vegan or ketogenic diet showed rapid and distinct changes in their immune system.

The small study, reported in the journal Nature Medicine, closely monitored the biological responses of people who sequentially ate vegan and ketogenic diets in random order. Those on the vegan diet showed responses that are linked to innate immunity, while the people on the ketogenic diet showed changes in their adaptive immunity, the pathogen-specific immunity that is built via exposures to our daily life and vaccines.

In addition, “both diets significantly and differentially impacted the microbiome and host-associated amino acid metabolism, with a strong downregulation of most microbial pathways following ketogenic diet compared with baseline and vegan diet,” the researchers wrote.

The distinct changes noted in the study related to both diets were observed consistently across the diversity of the participants demonstrating that the dietary changes consistently affect widespread and interconnected pathways in the body.

The investigators noted that nutrition affects all the processes that regulate the human immune system, and that a better understanding of the link between nutrition and host immunity provides an untapped opportunity to develop personalized, diet-based approaches to treating a range of human diseases including inflammatory disorders and cancer. Further, prior research has well established the association between a low-fat vegetarian or vegan diet with decreased inflammation, a reduced risk for cardiovascular disease, and a reduction in overall mortality.

However, the NIH investigators noted that given what is already known about the impact of diet on wellness and the development of disease, there is a significant lack of data on how nutritional interventions impact the human immune system. Further, studies in this area have only explored responses to only one diet at a time. This lack of data hampers the development of meaningful, proven nutritional interventions.

“Based on the highly variable responses of individuals to nutritional interventions and the high number of diets consumed, addressing how individuals respond to different diets remains an important line of research,” the NIH investigators stated in their published research.

The new study was conducted by a team in the NIH’s National Institute of Allergy and Infectious Diseases (NIAID) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) at the Metabolic Clinical Research Unit in the NIH Clinical Center. The small, 20-person study represented diverse ethnicity, race, gender, body mass index (BMI), and age. During the four-week study period, the participants ate as much as they wanted of one diet—either vegan or ketogenic—for the first two weeks, followed by as much as they wanted in the following two of the other diet.

People on the vegan diet which comprised roughly 10% fat and 75% carbohydrates chose to consume fewer calories than when they were on the ketogenic diet (76% fat, 10% carbohydrates).

Blood, urine, and stool samples were collected for analysis, which used a multi-omics approach to show the body’s biochemical, metabolic, cellular, and immune responses to the diets. The team also analyzed participants’ microbiome. All 20 people remained on-site for the duration of the study to allow for careful control of the participants’ diets.

Specifically, the vegan diet’s effects to the innate immune system included antiviral responses. The ketogenic diet affected biochemical and cellular processes associated with T cells and B cells, which play roles in adaptive immunity. The ketogenic diets affected the levels of a broader range of proteins in the blood plasma, as well as the proteins in range of other tissues including those in the brain and bone marrow. The ketogenic diet was also associated with changes in amino acid metabolism—an increase in human metabolic pathways for the production and degradation of amino acids and a reduction in microbial pathways for these processes—which might reflect the higher amounts of protein consumed by people on this diet.

The vegan diet promoted more pathways that are linked to red blood cells, such as the heme metabolism, which could be related to the higher iron content of the diet.

The investigators said the data obtained from the study demonstrates how rapidly the immune system responds to nutritional changes and while more research is needed to provide a more detailed understanding of how these dietary changes affect the interconnected pathways in the human body, the results, nonetheless, point to the potential of tailoring diets to either prevent disease development or to complement disease treatments, by slowing processes associated with cancer progression or neurodegenerative disorders.

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