The largest study to date of vegan, vegetarian, pescatarian, and meat-eating diets has identified that vegetarian diets are associated with a lower risk of several cancers, but a higher risk of one cancer type.
While vegetarian diets are considered to be healthy, there is a lack of information on how they may influence cancer risk due to the small numbers of vegetarians in diet-based studies.
The diets of 1.8 million people
The researchers identified nine prospective cohort studies through literature searches that either had high participant numbers or a high proportion of vegetarians. Pooling and harmonizing the data resulted in an analysis of 1.8 million people across three continents.
Participants had filled in food frequency questionnaires based on a typical diet at the start of each study, which were used to define the dietary groups of: meat eaters, poultry eaters, pescatarians, vegetarians, and vegans.
Diet classification
Meat eaters: consume red meat and/or processed meat.
Poultry eaters: eat poultry but not red or processed meat.
Pescatarians: eat fish, but not meat.
Vegetarians: do not consume red meat, processed meat, poultry, or fish but do eat dairy products and/or eggs.
Vegans: do not consume any animal products.
Most of the participants were meat eaters, with vegetarians forming 3.5% of the population studied, poultry eaters 3.1%, pescatarians 2.4%, and vegans 0.5%.
Differences in cancer risk
Incidents of cancer in 17 different sites were identified through cancer registries.
Compared to meat eaters, vegetarians had a lower risk of multiple myeloma (31% lower risk), kidney cancer (28%), pancreatic cancer (21%), prostate cancer (12%), and breast cancer (9%).
Vegetarians had nearly double the risk of developing squamous cell carcinoma of the oesophagus compared to meat eaters, which the researchers suggest could be linked to lower levels of micronutrients such as riboflavin or zinc in vegetarian diets, which are more abundant in animal products.
Pescatarians had a lower risk of breast, kidney, and bowel cancers compared to meat-eaters, while poultry eaters had a lower risk of prostate cancer.
Vegans had a 40% higher risk of bowel cancer when compared to meat eaters, to which Dr. Hilda Mulrooney, a reader in nutrition and health at London Metropolitan University (who was not involved in the research) noted: “This was based on a small number of cases, processed meat intakes among the meat eaters were low and after four years of follow-up the difference was no longer statistically significant.”
There were no statistically significant differences in risk for colorectal, stomach, liver, lung, endometrial, ovarian, mouth and pharynx, or bladder cancers, or non-Hodgkin lymphoma, leukaemia, and oesophageal adenocarcinoma in vegetarians compared to meat eaters.
What links a vegetarian diet with lower cancer risk?
The researchers propose that, as vegetarians and vegans are more likely to consume more fruit, vegetables, and fiber than meat eaters, the nutritional differences in their diets may lower their risk of certain cancers. The lack of processed meat in a vegetarian diet may also lower cancer risk.
“Among the 72,000 vegetarians and vegans included in our study, the numbers of cases for some cancers were small, which limits the certainty of some findings. Moreover, nutrient intakes and overall diet quality vary substantially within and between vegetarian populations,” said Dr. Yashvee Dunneram, first author of the study, a former postdoctoral epidemiologist at Oxford Population Health who is now a Faculty Fellow at Newcastle University.
The vegetarian diets among participants from Western Europe and North America featured relatively low intakes of saturated fat and high intakes of fiber, which are favorable characteristics for reducing cancer risk, the authors say.
“The authors suggested that the increased risk of some cancers observed in vegetarian groups may relate to inadequate intakes of some nutrients, and this needs further exploration,” said Mulrooney.
Further research to clarify how diet influences cancer risk could help people to mitigate risk through supplementation if nutrient deficiencies are indeed a causal factor in increasing squamous cell carcinoma of the oesophagus and bowel cancer in vegetarians and vegans, respectively.
The complexities of studying diet
The authors of the new study note that because vegetarian diets are defined by the foods that are not eaten rather than what is eaten, they could be high in less healthy foods.
In addition, there is no data on how much meat or fish the meat- or poultry-eaters and pescatarians consumed.
“In isolation, these findings cannot be used to infer a causal relationship between the consumption of meat and animal products in the diet and cancer risk,” said Dr. Nerys Astbury, an associate professor at the University of Oxford, who was also not involved in the study. “However, these new findings add to the strong existing evidence showing that eating red and processed meat is linked to a higher risk of certain cancers.”
“An important point to consider is that the data used in this study come from groups of people who were recruited at least 10 years ago—and in some cases as far back as the 1980s. Eating habits change over time. In the past, vegetarian and vegan diets were typically based on whole foods such as vegetables, beans, lentils, and pulses. Today, however, many vegetarian and vegan diets include a growing number of highly processed meat and dairy alternatives,” Astbury noted. “More research is needed to understand whether modern vegetarian and vegan diets—which often include ultra-processed alternatives—have the same health effects as the more traditional, whole-food versions of these diets.”
The authors of the research note that future research should examine metabolic factors influenced by diet that might, in turn, shape cancer risk. They also suggest that more data should be collected from vegans and in populations outside of Western Europe and North America to validate their findings.
Reference: Dunneram Y, Lee JY, Watling CZ, et al. Vegetarian diets and cancer risk: pooled analysis of 1.8 million women and men in nine prospective studies on three continents. Br J Cancer. 2026. doi: 10.1038/s41416-025-03327-4