Research Finds Drastic Diet Changes (Keto and Vegan) Affect Immune Health
New research is shedding light on how drastic dietary changes impact the immune system. Researchers found that switching to a vegan or ketogenic diet rapidly affects the immune system. Whether this is a positive or negative impact has yet to be determined. However, researchers were surprised at how quickly the changes happened. 
Study Design
This was a small study performed on only 20 people. Studies like this are done to see if it is worthwhile investigating a subject with larger cohorts. Conducting studies is pricey and time-consuming so they will often do smaller trials to make sure the larger ones are worth investigating.
During the study, participants stayed in the National Institute of Health Clinical Center to ensure their data was accurate. This allowed the researchers to control everything the subjects ate.
Participants were split into two groups: one adhered to the keto diet and the other adhered to a vegan diet. Each group stuck to their diet for 2 weeks and then switched to the other diet for the following 2 weeks.
Methods of Testing
Researchers used several methods to track what was happening within the participants during the study. Baseline levels were taken and then at specific intervals throughout the study.
The following were tested:
- Blood samples were taken and given the following tests
- Flow cytometry to test cell population composition — this was to figure out the changes within immune cell types between the two diets
- Bulk RNA sequencing tested the gene expression
- SomaLogic tested the protein composition
- Fecal samples were taken for metagenomic sequencing to see what changes happened within the gut microbial community
- Blood and urine samples were checked via metabolomic analysis
Dietary Options
Participants were allowed to eat whatever they wanted whenever they wanted. Their only restriction was that whatever they ate must be on the diet they were currently following.
Both diets contained nonstarchy vegetables, low quantities of digestible carbs, and limited highly processed foods.
In addition to these, the keto diet added animal products, including:
- Fish
- Poultry
- Meat
- Eggs
- Dairy
- Nuts
The keto diet is a high-fat and low-carb diet. The goal with the keto diet is to switch your energy source from carbs to fats. By doing this, there is an increase in ketone production, and often people drop weight quickly because of this. Because it is a low-carb diet, it is usually quite low in fiber because of the reduced intake of most fruits and some vegetables.
The vegan diet did not include any meat or animal products. They added the following to the base diet:
- Legumes
- Rice
- Root vegetables
- Soy products
- Corn
- Lentils
- Peas
- Whole grains
- Bread
- Fruit
The vegan diet, as compared to the keto diet, is very high in fiber and much higher in dietary sugars. Since the sugars in the vegan diet are most often in the form of fruits, it isn’t quite as concerning as the Western diet (high in processed sugars and low in fiber).
Study Findings
Participants on a vegan diet consumed fewer calories. Those on the keto diet consumed more fatty and amino acids, which is expected from a diet high in animal products.
In both diets, there were significant changes in immune cells. There was a significant decrease in naive CD8 T cells. Meanwhile, there was an increase in activated CD4 T cells, effector CD4 T cells, and effector CD8 T cells.
Whether the changes were due to the reduction in their highly processed food intake or the specific diets they began consuming will need more research to determine.
There weren’t many differences observed between diets in regard to the proteasome. The major factor here seemed to be sex differences rather than dietary differences. Women experienced more changes on the keto diet than on the vegan diet, however, other than that things were relatively similar.
Some other changes that only happened for each individual diet are as follows.
Keto Diet Changes to Immune Cells
Those on the keto diet experienced higher activation of regulatory T cells and CD16+ natural killer cells.
The keto diet was associated with an upregulation in the pathways associated with adaptive immunity like the activation of T cells. The upregulation is expected to be because of the T and B cells. This included an enrichment of B cells, plasma cells, and natural killer cells.
The keto diet also boosted lymph cell production.
Vegan Diet Changes to Immune Cells
Those on the vegan diet experienced a higher activation of T helper cells and activated natural killer cells.
As opposed to the keto diet, the vegan diet showed an upregulation in the innate immune pathways. This upregulation is expected to be driven by the neutrophils. With this, there was a noted increase in type I interferon signatures and responses.
The vegan diet was associated with more red blood cell production, likely due to the higher iron intake.
Gut Microbiome Differences Between Diets
When it comes to the gut microbiome, there are a lot of different things to look at. Considering there are trillions of microorganisms ranging from bacteria to fungi, many things are at play.
The changes to the gut microbiome were different between diets. However, these changes weren’t much different from what we had already known the diets to do in regards to microbial composition.
The following phyla were the most impacted by dietary changes:
- Actinobacteria
- Bacteroidetes
- Firmicutes — the most highly affected group with 26 species being altered and 18 of them being more affected by the vegan diet
- Proteobacteria
The keto diet held true to a higher abundance of species like Bacteroides sartorii and Bacteroides vulgatus. Both are associated with higher animal protein intake. Meanwhile, the vegan diet showed an expected increase in Bifidobacterium longum and Bifidobacterium pseudocatenulatum which are common in high-fiber diets.
There was also an interesting downregulation of amino acids and vitamin synthesis with the keto diet. This suggests that the diet itself was providing these and the body no longer had to rely on the gut microbiome to provide the amino acids and vitamins. More research is needed to understand these effects on host health.
What does this research mean?
This study has shown a more distinct change in subjects on the keto diet than the vegan diet. This is likely because the vegan and standard diets are based on carbohydrate intake whereas the keto diet is based on fat intake as the energy source.
Researchers want to replicate this study on a larger scale to see how it affects a more generalized population. They also want to see if these changes are for a positive or negative impact on the participant. While they are seemingly positive changes, we do not know how they affect the body long term.
This is an exciting pathway to understand how different diets affect our immune system and overall health.
To read more about a proven way to boost your immune system, check out our article here on polyphenol’s effects on the immune system.