Researchers looked at blood cell counts in vegetarians compared to people who eat meat using data from a large US health survey. They found that vegetarians had slightly lower red blood cells and hemoglobin (a protein that carries oxygen), but their white blood cells—which fight infections—were similar to meat-eaters. The study included over 8,000 people and is one of the largest to examine this question. While some differences appeared, they weren’t as dramatic as some smaller studies suggested. The findings suggest that a well-planned vegetarian diet doesn’t significantly harm immune cell counts.

The Quick Take

  • What they studied: Whether vegetarians have different numbers of blood cells compared to people who eat meat, particularly white blood cells that help fight infections
  • Who participated: Over 8,000 Americans from a national health survey, including 98 people who eat dairy and eggs but no meat, 110 people who eat mostly plants with occasional meat, and thousands of regular meat-eaters
  • Key finding: Vegetarians had slightly lower red blood cells and hemoglobin levels, but their white blood cell counts were similar to meat-eaters—not the significant differences some earlier studies claimed
  • What it means for you: If you’re considering a vegetarian diet, you don’t need to worry that it will weaken your immune system based on white blood cell counts. However, you should ensure adequate vitamin B12 and iron intake, as vegetarians in this study had lower oxygen-carrying capacity in their blood

The Research Details

This was a cross-sectional study, which means researchers took a snapshot of blood cell counts at one point in time rather than following people over years. They used data from the National Health and Nutrition Examination Surveys (NHANES), a large, nationally representative survey that collects health information from thousands of Americans. The researchers compared three groups: people who eat dairy and eggs but no meat (lacto-ovo-vegetarians), people who eat mostly plants with occasional meat (semi-vegetarians), and regular meat-eaters (omnivores). They measured various types of blood cells and adjusted their analysis for factors like age, body weight, and nutrient intake that might affect blood cell counts.

The strength of this study is its large size and use of probability-based sampling, meaning the results better represent the general US population than smaller studies using convenience sampling. The researchers used statistical methods to account for differences between groups, such as vegetarians being younger and having healthier body weights on average.

Previous smaller studies reported conflicting results about whether vegetarians have fewer white blood cells. This larger, more representative study helps clarify whether those findings were real or just due to chance or study design problems. Understanding blood cell counts matters because white blood cells are crucial for fighting infections and disease, so if vegetarian diets significantly lowered them, it would be a health concern.

This study is more reliable than many previous ones because it used a large, nationally representative sample rather than convenience sampling. However, it’s still a snapshot in time rather than following people over years, so we can’t prove that vegetarian diets cause the observed differences. The vegetarian groups were relatively small (98 and 110 people), which limits how confident we can be about some findings. The study adjusted for many factors that could affect results, which strengthens the conclusions.

What the Results Show

When comparing vegetarians to meat-eaters, white blood cell counts were actually similar between groups—contrary to what some smaller studies suggested. This was true even after accounting for differences in age, body weight, and other factors. The most notable finding was that vegetarians had lower red blood cell counts and hemoglobin levels, which is the protein in red blood cells that carries oxygen throughout your body.

Interestingly, in vegetarians specifically, white blood cell counts were related to body weight and selenium intake (a mineral found in foods like nuts and fish). For every additional microgram of vitamin B12 that vegetarians consumed, their white blood cell counts increased slightly. This suggests that adequate B12 intake may be important for maintaining normal immune cell counts in vegetarians.

The researchers noted that the differences in red blood cells and hemoglobin were directionally consistent with previous studies, meaning other researchers had found similar patterns. However, the differences in white blood cells and neutrophils (a specific type of white blood cell) were not statistically significant, meaning they could have occurred by chance.

The study found that vegetarians in the survey were younger, had healthier body weights, and included a higher proportion of women compared to meat-eaters. These differences could partially explain some of the blood cell variations observed. The correlation between body weight and white blood cell counts in vegetarians suggests that maintaining a healthy weight may be important for immune function regardless of diet type.

This study helps resolve conflicting findings from earlier research. Some smaller studies reported that vegetarians had significantly lower white blood cell counts, but this larger study found no significant difference. The researchers suggest that previous studies may have had design problems or been affected by chance variation due to small sample sizes. The findings about lower red blood cells and hemoglobin in vegetarians align with previous research and likely reflect lower iron intake or absorption in plant-based diets.

The vegetarian groups were relatively small (98 and 110 people), which limits how confident we can be about some findings. The study measured blood cells at only one point in time, so we can’t determine whether vegetarian diets cause these differences or if other factors are responsible. The study couldn’t fully account for diet quality—some vegetarians may eat healthier diets than others. Additionally, the study couldn’t determine whether any observed differences actually affect health outcomes or disease risk.

The Bottom Line

Based on this evidence (moderate confidence): If you’re considering a vegetarian diet, you don’t need to worry about it significantly lowering your infection-fighting white blood cells. However, ensure adequate intake of vitamin B12 (found in fortified foods or supplements), iron (from beans, lentils, fortified cereals), and selenium (from nuts, seeds, whole grains). If you’re vegetarian, consider periodic blood tests to monitor red blood cell counts and hemoglobin levels, as these were lower in vegetarians.

This research is relevant for people considering vegetarian diets, particularly those concerned about immune function. It’s also important for healthcare providers advising vegetarian patients. People with existing blood disorders or those taking medications affecting blood cells should discuss diet changes with their doctor. This study is less relevant for people already following well-planned vegetarian diets with adequate nutrient intake.

Blood cell counts can change relatively quickly with dietary changes—typically within weeks to months if nutrient intake is inadequate. However, if you maintain proper nutrition, you shouldn’t see concerning changes in white blood cell counts. Any changes in red blood cells and hemoglobin may take longer to develop and reverse.

Want to Apply This Research?

  • Track daily vitamin B12 intake (target: 2.4 mcg for adults) and iron intake (target: 8-18 mg depending on age/sex) using the app’s nutrient tracking feature. Set weekly reminders to log these nutrients specifically.
  • If vegetarian or considering it, use the app to identify and log B12-fortified foods (cereals, plant milks, nutritional yeast) and iron-rich plant foods (beans, lentils, spinach, fortified grains) at each meal. Set a goal to include at least one iron-rich food daily.
  • Use the app to track nutrient intake trends over 3-month periods. If following a vegetarian diet, schedule annual blood work reminders to monitor hemoglobin and red blood cell counts. Log any symptoms of anemia (fatigue, shortness of breath) to discuss with healthcare provider.

This research is observational and cannot prove that vegetarian diets cause changes in blood cell counts. Individual responses to dietary changes vary significantly. Before making major dietary changes, especially if you have existing health conditions, anemia, or take medications affecting blood cells, consult with your healthcare provider or registered dietitian. This summary is for educational purposes and should not replace professional medical advice. If you experience symptoms like unusual fatigue, shortness of breath, or frequent infections, seek medical evaluation regardless of your diet type.