Researchers wanted to understand how eating only plants affects your body’s defense system compared to eating meat. They had 57 healthy adults follow either a vegan diet or a meat-heavy diet for 8 weeks. The study found that people eating the vegan diet had fewer white blood cells and certain immune cells than those eating meat. While this might sound concerning, the researchers think it could actually mean the vegan diet reduces inflammation in the body—which might be helpful for people with certain health conditions. However, this was a short study in healthy people, so we need more research to understand what this really means for your health.

The Quick Take

  • What they studied: Whether eating a plant-based diet for 8 weeks changes the types and amounts of immune cells in your blood compared to eating a meat-rich diet
  • Who participated: 57 healthy adults (the paper doesn’t specify age, gender, or other details) who were randomly assigned to either eat only plants or eat at least 150 grams of meat daily for 8 weeks
  • Key finding: People eating the vegan diet had lower counts of white blood cells, lymphocytes (a type of immune cell), and B-cells compared to the meat-eating group. The vegan group also had decreases in platelets and neutrophils (another immune cell type)
  • What it means for you: A plant-based diet may reduce inflammation in your body, which could potentially help people with inflammatory conditions. However, this study only looked at healthy people for 8 weeks, so we can’t yet say whether this is good or bad for your health long-term

The Research Details

This was a randomized controlled trial, which is considered one of the strongest types of research. Researchers split 57 healthy adults into two groups: one group ate only plant-based foods (no meat, dairy, or eggs) while the other group ate at least 150 grams of meat every day. Both groups ate the same number of calories—the only difference was the type of food. The study lasted 8 weeks, and researchers measured blood cell counts and immune cell types at the beginning and end.

The researchers used a technique called immunophenotyping to identify and count specific types of immune cells in the blood. This is like taking a detailed inventory of your body’s defense system rather than just counting total white blood cells.

By comparing two groups eating different diets with the same calories, researchers could see if the diet itself—not just eating more or less food—affects immune cells. This approach helps separate the effects of diet type from the effects of eating more or fewer calories. The 8-week timeframe was long enough to see changes but short enough to control other factors that might affect results.

This study has several strengths: it was randomized (reducing bias), it had a control group for comparison, and it measured specific immune cells using advanced lab techniques. However, the study only included 57 people, which is a relatively small number. The paper doesn’t provide details about participants’ ages, genders, or backgrounds, making it harder to know if results apply to everyone. The study was also short (8 weeks), so we don’t know if these changes last longer or what happens when people return to normal eating.

What the Results Show

After 8 weeks, the vegan diet group had noticeably fewer white blood cells (the main infection-fighting cells) compared to the meat-eating group. Specifically, the vegan group had about 5.17 thousand white blood cells per microliter of blood, while the meat group had about 5.39 thousand—a small but statistically significant difference.

The vegan group also had fewer lymphocytes (a specific type of white blood cell important for fighting infections and diseases). The vegan group had about 1.80 thousand lymphocytes per microliter compared to 2.06 thousand in the meat group. Interestingly, this difference happened because the meat-eating group’s lymphocytes actually increased during the study, while the vegan group’s stayed relatively stable.

When researchers looked at specific immune cell types, they found that the vegan group had fewer B-cells (immune cells that make antibodies) and CD8+ T-cells (immune cells that kill infected cells). The vegan group’s B-cells dropped from about 215 cells per microliter at the start to about 172 cells per microliter after 8 weeks.

The vegan group also showed decreases in platelets (cells that help blood clot) and neutrophils (another type of white blood cell that fights bacteria). The meat-eating group’s platelets and neutrophils stayed relatively stable or increased slightly.

The study also measured CD3+ T-cells (a broader category of immune cells) and found differences between groups. These secondary findings support the main conclusion that a plant-based diet appears to reduce various types of immune cells. The researchers noted that these changes happened even though both groups ate the same number of calories, suggesting the type of food—not the amount—drove the differences.

Previous research has suggested that plant-based diets have anti-inflammatory properties and may help people with autoimmune diseases (conditions where the immune system attacks the body). This study adds to that evidence by showing that plant-based diets do appear to affect immune cell counts. However, most previous studies looked at people with existing health conditions, while this study looked at healthy people. The results align with the theory that plant-based diets reduce inflammation, though the mechanism isn’t completely understood yet.

This study has several important limitations to consider. First, it only included 57 people, which is a small sample size—larger studies might show different results. Second, the study only lasted 8 weeks, so we don’t know if these changes continue, reverse, or stabilize over months or years. Third, the paper doesn’t describe the participants in detail (age, gender, ethnicity, health status), making it unclear whether results apply to everyone. Fourth, the study only looked at healthy people, so we can’t assume these results apply to people with health conditions. Finally, while the study shows that immune cell counts changed, it doesn’t prove this is beneficial or harmful—lower immune cell counts could be good (less inflammation) or concerning (weaker immune response), and we need more research to understand which.

The Bottom Line

Based on this single study, we cannot make strong recommendations about switching to a plant-based diet specifically to change your immune system. The evidence is interesting but preliminary. If you’re considering a plant-based diet for other reasons (environmental, ethical, or general health), this study suggests it may reduce inflammation, which could be beneficial. However, consult with a healthcare provider or registered dietitian, especially if you have a health condition or take medications. Confidence level: Low to Moderate—this is one small, short-term study that needs to be confirmed by larger, longer research.

This research may be most relevant to people with inflammatory conditions (like rheumatoid arthritis or inflammatory bowel disease) who are considering dietary changes, since the anti-inflammatory effects might help them. People interested in plant-based diets for any reason should know about this potential immune effect. However, healthy people eating a balanced omnivorous diet shouldn’t be concerned about their immune function based on this study alone. People who are immunocompromised or have conditions requiring strong immune function should discuss plant-based diets with their doctor before making major changes.

If someone switched to a plant-based diet, this study suggests immune cell changes could occur within 8 weeks. However, we don’t know if these changes happen gradually over those 8 weeks or suddenly, and we don’t know if they continue to change after 8 weeks. Any health benefits from reduced inflammation would likely take weeks to months to notice, if they occur at all.

Want to Apply This Research?

  • If users are trying a plant-based diet, they could track their energy levels, digestion quality, and any inflammation symptoms (joint pain, swelling, skin issues) weekly using a simple 1-10 scale. This helps them notice personal changes even though blood tests aren’t practical for daily tracking.
  • Users could set a goal to gradually increase plant-based meals while tracking how they feel. For example: ‘Add one plant-based dinner per week’ or ‘Replace one meat-based lunch with a plant-based option.’ The app could remind them to log their meals and any physical changes they notice.
  • For long-term tracking, users could schedule monthly check-ins where they reflect on overall energy, digestion, inflammation symptoms, and how they feel. If they’re interested in the immune cell changes mentioned in this study, they could discuss getting blood work done with their doctor every 3-6 months to see if their immune cell counts change over time.

This study provides preliminary evidence about how plant-based diets may affect immune cell counts in healthy adults. However, this is a single small study lasting only 8 weeks, and results should not be interpreted as medical advice. Lower immune cell counts do not necessarily mean better or worse health—the long-term health implications are unknown. If you have a health condition, take medications, or are immunocompromised, consult with your healthcare provider or registered dietitian before making significant dietary changes. This research is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of your doctor or qualified health professional with any questions you may have regarding your health or a medical condition.