Vegan and Ketogenic Diets Prompt Striking, Rapid Changes in the Immune System

A close look at new research exploring how switching to a vegan or ketogenic diet can quickly—but differently—transform the body's immune response and microbiome.

By Sneha Tete, Integrated MA, Certified Relationship Coach

Created on Sep 28, 2025

A close look at new research exploring how switching to a vegan or ketogenic diet can quickly—but differently—transform the body's immune response and microbiome.

Vegan vs. Ketogenic Diets: New Research Reveals Powerful Effects on Immunity

The diets we choose do more than regulate weight or energy—they powerfully and rapidly influence our immunity and gut health. A new study by the National Institutes of Health (NIH) brings this into sharp relief, showing that switching to either a vegan or ketogenic (keto) diet causes significant and distinct changes in the immune system in little more than two weeks. The findings raise important new questions about how nutrition can be used strategically to bolster health, treat disease, and even tailor the body’s response to pathogens.

What Did the Study Investigate?

Researchers conducted a tightly controlled, month-long clinical study where 20 diverse adults consumed a vegan diet for two weeks and then a ketogenic diet for two weeks (or vice versa), living onsite for precise monitoring. The project was designed to provide deep insights into how rapid dietary changes affect both the body’s innate immunity (the “first response” system against foreign invaders) and adaptive immunity (the system that remembers specific pathogens after previous exposure or vaccination). The study also investigated how these diets altered the gut microbiome—the billions of bacteria living in the digestive tract that play a vital role in health.

Vegan Diet: High in fiber and carbohydrates, very low in fat, excludes all animal products.
Ketogenic Diet: Very high in fat, low in carbohydrates, includes animal-derived and plant-derived fats, restricts sugars and grains.

Key Findings: How Each Diet Changed the Immune System

The research uncovered that both diets triggered large, measurable shifts in immune pathways—but in strikingly different ways.

The Vegan Diet: Boosting Innate Antiviral Defenses

Adopting a vegan diet led to an activation of innate immune pathways, particularly those associated with antiviral responses:

Heightened nonspecific immunity: The body’s general immune barriers became more active, potentially bolstering defenses against a wide range of pathogens.
Upregulation of red blood cell-related pathways: Pathways related to heme metabolism and red blood cells were more prominent, likely due to the higher plant-based iron content.
Shift in gut bacteria: The vegan diet increased the presence of gut bacteria species and metabolic pathways typically linked to fiber-rich diets.
Lower calorie consumption: Participants unconsciously consumed fewer calories while on the vegan diet, even though all meals were ad libitum (as much as they wanted).

The Ketogenic Diet: Strengthening Adaptive Immunity

Switching to a ketogenic diet directed the immune system’s focus toward the adaptive immune arm:

Activation of adaptive responses: The keto diet upregulated processes involving T and B cells, the “memory” cells that respond to specific pathogens and are the basis of how vaccines work.
Wide systemic effects: The keto diet yielded measurable shifts across a broader set of proteins in the blood, including those from the blood, brain, and bone marrow.
Amino acid metabolism: Keto increased human metabolic pathways for processing amino acids due to the higher protein intake and reduced microbial (gut bacteria) pathways for this function.
Altered microbiome: There was a noticeable shift in the gut bacterial species—distinct from those seen in the vegan phase—a pattern previously associated with high-fat, low-carb diets.

Unpacking the Science: How Diets Shape Immunity and Microbiome

Delving deeper, the study’s multi-omics approach (analyzing biochemistry, cells, proteins, and gut bacteria simultaneously) revealed:

Even short-term dietary changes (as little as two weeks) are enough to remodel immune signatures.
The order of diet (whether vegan first or keto first) did not alter the outcome: it was the diet content itself, not the transition, that produced the effects.
Vegans experienced a surge in activated T helper cells and natural killer (NK) cells, key players in innate antiviral defenses.
Individuals on keto showed an uptick in activated regulatory T cells and CD16+ NK cells, which are tied to controlling inflammation and mounting specific immune responses.

Pivotal to both diets, but in distinct ways, were changes in the gut microbiome:

Vegan phase: Greater abundance of bacteria that ferment fiber and produce beneficial compounds like short-chain fatty acids.
Keto phase: An increase in bacteria favoring fat and protein digestion, alongside reduced diversity in microbial processes for amino acid metabolism.

Comparing the Two Diets: Nurturing Different Aspects of Immunity

Aspect	Vegan Diet	Ketogenic Diet
Primary Immune Activation	Innate (general, early response)	Adaptive (specific, memory-based response)
Main Pathways Enriched	Antiviral, Red Blood Cell, Heme metabolism	T & B Cells, Regulatory immune cells, Amino Acid Metabolism
Microbiome Impact	Higher fiber fermenters, increased microbial diversity	Increased protein/fat digesters, decreased microbial amino acid pathways
Potential Dietary Issues	Lower calorie intake, higher iron	Higher calorie intake, potential for nutrient imbalances
Systemic Changes	Narrower range	Broader range (affecting blood, brain, bone marrow)

What Does This Mean for Health and Disease?

This research unlocks new possibilities in the field of precision nutrition—the idea that food choices can be tailored to prevent (or help manage) specific diseases. For example:

People at risk for viral infections or whose innate immunity is compromised might benefit from dietary shifts toward vegan patterns, at least for short periods.
Those seeking to boost adaptive immunity—for instance, to complement vaccine effectiveness—might benefit from short-term ketogenic protocols, though more research is needed.
This work suggests that therapeutic diets could one day be prescribed alongside standard treatments, such as cancer immunotherapy or auto-immune therapies, to steer the immune system in helpful directions.

However, the study’s authors and outside experts stress caution. The observed immune changes’ long-term health implications remain unclear, and both diets should be considered with a full understanding of their possible risks (such as nutritional deficiencies or unwanted metabolic effects).

Expert Perspectives: Interpreting the Findings

Dr. Yasmine Belkaid, President of Institut Pasteur and study senior author, emphasized the importance of these results: “Our study demonstrates just how quickly the immune system can be remodeled by diet—and by extension, how powerful dietary choices can be for health.”

Nutrition researcher Dr. Kevin Hall, another key study leader, underscored the need for more research: “These findings are exciting but are just a starting point. We need larger, longer-term studies before making definitive dietary recommendations based on immune effects alone.”

What Are the Differences Between Innate and Adaptive Immunity?

Innate immunity is the body’s first defense line—non-specific, fast, and present at birth. Physical barriers (like skin), chemical defenses, and immune cells such as neutrophils and NK cells eliminate many threats before they establish infection.
Adaptive immunity develops over time, targeting specific pathogens. It relies on T cells and B cells, creates immunological memory (e.g., after vaccines or infections), and is slower to react but highly specialized.

The Study in Context: Methodology and Limitations

This was a rigorous, highly controlled trial:

Each of the 20 participants stayed at the research facility full-time for 4 weeks.
Diets were isocaloric (participants could eat as much as they wanted), maximizing real-world relevance.
Extensive biological sampling: Blood, urine, and stool were collected regularly for comprehensive analysis.
Modern multi-omics techniques assessed the interplay between metabolites, proteins, immune cells, and bacteria.

Limitations include:

A small sample size (n=20) and short duration limit conclusions about long-term health outcomes.
Healthy adults were studied—effects in older people, children, or those with chronic disease may differ.
Diets were formulated by researchers and may not resemble “average” vegan or ketogenic diets in the real world.
The study can’t specify whether health outcomes from these immune changes are beneficial, harmful, or mixed.

Frequently Asked Questions (FAQs)

Q: Can switching diets really affect my immune system that quickly?

A: Yes. The research shows that even a 2-week shift to vegan or ketogenic diets can cause rapid and significant changes in immune cell activity and gut bacteria, though more research is needed to understand lasting impacts.

Q: Are these immune changes good or bad for my health?

A: It depends. The study showed the immune system becomes more active in certain pathways, but whether this is beneficial or risky in the long term isn’t yet known. It’s best to consult a healthcare professional before making dramatic dietary shifts, especially for health reasons.

Q: Should I switch to vegan or ketogenic diets for immune health?

A: Not solely on the basis of this research. Both diets have benefits and potential drawbacks. Your best choice depends on your overall health, nutritional needs, and doctor’s advice.

Q: Are the results relevant for people with chronic diseases or immune disorders?

A: The trial was conducted in healthy adults, so additional studies are needed to understand the effects for other groups, especially those with medical complexities.

Takeaway: Diet as a Driver of Immunity and Gut Health

In summary, emerging science confirms that major dietary changes—vegan or ketogenic—are not just about metabolism or weight. These eating patterns rapidly reshape our immune function and the communities of bacteria we host, with effects observable within weeks. As research progresses, personalized nutrition may one day help optimize immune health or complement medical care, but individualized guidance remains essential.

References

Author

Sneha TeteBeauty & Lifestyle Writer

Sneha is a relationships and lifestyle writer with a strong foundation in applied linguistics and certified training in relationship coaching. She brings over five years of writing experience to thebridalbox, crafting thoughtful, research-driven content that empowers readers to build healthier relationships, boost emotional well-being, and embrace holistic living.

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