Switching to a vegan or ketogenic diet could have rapid impact on the immune system

Researchers at the National Institutes of Health discovered rapid and distinct immune system changes in a small study of people who switched to a vegan or ketogenic (also known as keto) diet. Scientists closely monitored the biological responses of people who ate vegan and keto diets for two weeks in random order.

They discovered that the vegan diet elicited responses associated with innate immunity (the body's non-specific first line of defence against pathogens), whereas the keto diet elicited responses associated with adaptive immunity (pathogen-specific immunity developed through exposures in daily life and vaccination). Metabolic changes and shifts in the participants' microbiomes (bacterial communities that live in the gut) were also observed. More research is needed to determine whether these changes are beneficial or detrimental, as well as the impact they may have on nutritional interventions for diseases like cancer and inflammatory conditions.

The scientific understanding of how various diets affect the human immune system and microbiome is limited. Therapeutic nutritional interventions, which involve changing one's diet to improve health, are poorly understood, with few studies directly comparing the effects of multiple diets. The keto diet is characterised by low carbohydrate intake and a high fat content. Vegan diets exclude animal products and are typically high in fibre and low in fat.

Researchers from the National Institute of Allergy and Infectious Diseases (NIAID) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) conducted the study at the Metabolic Clinical Research Unit of the NIH Clinical Centre.

The 20 participants were diverse in terms of ethnicity, race, gender, BMI, and age. Each person ate as much as they wanted of one diet (vegan or keto) for two weeks before switching to the other diet for two weeks. People on the vegan diet, which contained about 10% fat and 75% carbohydrates, ate fewer calories than those on the keto diet, which contained about 76% fat and 10% carbohydrates. During the study, blood, urine, and stool were collected for analysis.

The effects of the diets were investigated using a "multi-omics" approach that analysed multiple data sets to assess the body's biochemical, cellular, metabolic, and immune responses, as well as changes in the microbiome.

Participants stayed on-site throughout the month-long study, allowing for precise control of the dietary interventions. Switching exclusively to the study diets resulted in significant changes in all participants.

The vegan diet had a significant impact on pathways related to the innate immune system, including antiviral responses. In contrast, the keto diet resulted in significant increases in biochemical and cellular processes associated with adaptive immunity, such as T and B cell pathways.

The keto diet had a greater impact on blood plasma protein levels than the vegan diet, as well as proteins from a wider range of tissues, including the blood, brain, and bone marrow. The vegan diet increased red blood cell-linked pathways, including those involved in heme metabolism, which could be attributed to the diet's higher iron content.

Furthermore, both diets altered the microbiomes of the participants, resulting in shifts in the abundance of gut bacterial species previously linked to the diets. The keto diet was linked to changes in amino acid metabolism, including an increase in human metabolic pathways for amino acid production and degradation and a decrease in microbial pathways for these processes, which could be attributed to the higher protein intake of people on this diet.

Regardless of participant diversity, the two diets caused distinct metabolic and immune system changes, demonstrating that dietary changes consistently affect widespread and interconnected pathways in the body. More research is needed to determine how nutritional interventions affect specific immune system components. According to the authors, the findings of this study show that the immune system responds surprisingly quickly to nutritional interventions. The authors propose that diets can be tailored to prevent disease or supplement disease treatments, such as slowing the progression of cancer or neurodegenerative disorders.

Reference:Verena M. Link, Poorani Subramanian, Foo Cheung, Kyu Lee Han, Apollo Stacy, Liang Chi, Brian A. Sellers, Galina Koroleva, Amber B. Courville, Shreni Mistry, Andrew Burns, Richard Apps, Kevin D. Hall, Yasmine Belkaid. Differential peripheral immune signatures elicited by vegan versus ketogenic diets in humans. Nature Medicine, 2024; DOI: 10.1038/s41591-023-02761-2