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A study published in the British Journal of Cancer looks at vegetarian and other diets and cancer incidence.
Dr Michael Jones, staff scientist in the Clinical Cancer Epidemiology Group at The Institute of Cancer Research, London, said:
“This looks like a well conducted and interesting study.
Does the press release accurately reflect the science?
“The press release accurately reflects the science, and it appropriately cautious in its conclusions.
Is this good quality research? Are the conclusions backed up by solid data?
“This is good quality research for this type of study and data. The researchers pooled data from over 1.8M people who were members of cohort studies that were either high in proportion of vegetarians or were from very large studies that would be expected to contain a large number of vegetarians. The researchers harmonised the data centrally (except for one study from Taiwan, for data protection reasons) and were able to adjust for potential confounding factors; this is an advantage of pooling individual level data rather than the more limited approach that only pools results in a meta-analysis. The method of analysis is appropriate and the researchers were careful when making exclusions, defining the follow-up time, the ascertainment of cancers in the cohorts, and conducting sensitivity analyses to assess the robustness of the results. The length of follow-up on average was 16 years, which is reasonable for studies of cancer.
Have the authors accounted for confounders? Are there important limitations to be aware of?
“By centrally pooling and harmonising the data from individual studies the researchers were able to adjust for some important potential confounders.
“The results are restricted to cancer sites with a relatively large number of cases, but even then the numbers of cancers occurring at each site was low in those not eating red meat and as a consequence the confidence intervals are large around some results. Also, when presenting a large number of results (multiple testing) some results may be statistically significant by chance, but the authors make some allowance for this (by using a False Discovery Rate). The researchers are aware of these limitations and do not overstate the results but interpret findings cautiously.
“The type of diet would typically be ascertained by questionnaire at recruitment to the individual study. The researchers did not have information on diet before recruitment so do not know for how long participants had maintained a particular diet or when they had started. The researchers did report that in a subsample of participants a majority of participants had remained vegetarian. Any misclassification of diet might possibly attenuate the relative risks reported. There could also be biases in the results if reason for change in past dietary pattern was linked to other lifestyle changes that affected cancer risk, but (unfortunately) this level of information was not available for analysis.
What are the implications in the real world? Is there any overspeculation?
“The researchers point out that not all vegetarian or vegan diets are identical. This work pooled studies from a small number of different countries, so it is not clear how generalisable the results are to all types of vegetarian or vegan diet.
“In an observational study like this, the associations seen do not prove causation however they do suggest future avenues for research.
“And it should be noted that the work looks at differences in people who eat meat and people who are vegetarian. It does not address the question of how risk changes if a meat eater were to change diet and become a vegetarian.”
Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:
“This is an important pooled analysis of data on 1.8 million men and women regarding the risk of the cancer at several sites comparing people who eat meat with those who avoid it (pescatarians, vegetarians and vegans). The strength of the study is the long period of follow-up (16 years) and the large number of incident cancers recorded and the robust statistical analysis. The study showed that 68-89% of those who reported being vegetarians and baseline were still vegetarians after 14 years of follow-up.
“The incidence of many cancers was lower in the vegetarians particularly those cancers associated with obesity, alcohol intake and smoking as would be predicted. However, the study found a higher incidence of squamous cell cancer of the oesophagus in vegetarians for reasons that are uncertain. A more surprising finding was that there was no evidence that vegetarians had a lower risk of colorectal cancer than meat-eaters but that vegans had statistically significant 40% higher risk! A novel observation was that people who ate fish but not meat/poultry (pescatarians) had a 15% lower risk of colorectal cancer.
“A limitation of the study is that many comparisons were made making it more likely that some differences could be statistically significant by play of chance. The findings on pescatarians and vegans are less robust because there were fewer people following these diets than vegetarians.
Interpretation:
“There is currently much public interest in the gut microbiome particularly in relation to colorectal cancer. Several studies have demonstrated marked change in the microbiome when shifting from a mixed diet containing meat to plant-based/vegan diets. It had been suggested that this change would the decrease risk of colon cancer. The findings of this study question this hypothesis because vegetarians who have followed a plant-based diet containing no meat for many years didn’t have a lower risk of colorectal cancer. Most previous studies show a greater risk of colorectal cancer in people who eat large amounts of red and processed meat compared to people who eat moderate amounts. Consequently, some caution is needed here because the comparison group of meat eaters in this latest study were not consumers of large amounts of meat.”
Dr Dagfinn Aune, Research Fellow at the Department of Epidemiology and Biostatistics, Imperial College London, said:
Does the press release accurately reflect the science?
“Yes, the press release reflects the research very well.
Is this good quality research? Are the conclusions backed up by solid data?
“This is high quality research covering data from 1.8 million participants in nine prospective cohort studies from the US, Europe and Asia. Efforts have been made to standardize the analyses and adjustment for confounders across cohort studies, which is an advantage.
How does this work fit with the existing evidence?
“This work is largely consistent with several previous cohort studies that have been published (some of which are included in the current analysis) and they are also largely consistent with our own work at Imperial College (to be published soon), which shows a lower cancer risk overall as well as of several specific cancers among vegetarians when compared to meat eaters. The study found a lower risk of pancreatic, breast, prostate, and kidney cancer, and multiple myeloma among vegetarians when compared to meat eaters, but a higher risk of esophageal squamous cell carcinoma. There may be hints toward a lower risk for some additional cancers in vegetarians, but further work may be needed as the results were not statistically significant. Vegans were found to be at higher risk of colorectal cancer, which could be due to low calcium intakes (because of avoidance of dairy products or too low intake of fortified foods). However, because of small numbers of vegans, associations for the remaining cancers were not clear and larger cohorts with much larger number of vegans are needed. However, some previous cohorts have found a lower overall cancer risk in vegans (and vegetarians) than among omnivores1, but the current analysis did not look at overall cancer risk. In addition, pescatarians had lower risk of colorectal, breast and kidney cancer, while poultry eaters had lower risk of prostate cancer when compared to meat eaters.
“Even if the study is large, it may not have had sufficient statistical power to detect clear associations across all the investigated cancer sites (e.g. mouth and pharynx, oesophageal adenocarcinoma, stomach, liver, and endometrial cancer, or non-Hodgkin’s lymphoma). Surprisingly, there was no reduction in risk of colon or colorectal cancer among vegetarians in the study, which is at odds with several previous studies (most previous studies reported reductions in risk of 10-40%, although the findings in individual studies were not always statistically significant). The null results for colorectal cancer are also at odds with a large body of evidence showing that red and processed meat increases colorectal cancer risk, while higher intakes of fibre and whole grains reduces risk. Nevertheless, it’s possible that lumping all meat eaters (regardless of how much or little meat they ate) together may have diluted any effects of vegetarian diets on cancer risk, particularly if meat intake was low in some studies.
“There is also increasing evidence that dietary changes during follow-up can attenuate associations between diet and disease risk toward the null. A limitation is that most of the included studies only had a baseline dietary assessment in the full cohort and although the authors stated that dietary adherence was relatively high (in subsets of participants with repeated measures), it is likely that larger dietary changes can occur with a longer duration of follow-up. To what extent this could have attenuated or obscured some associations warrants further investigation.
Have the authors accounted for confounders? Are there important limitations to be aware of?
“The authors have adjusted for relevant confounders including age, sex, region, smoking, alcohol, height, physical activity, education, living with a partner, ethnic group, and for female-specific cancers for parity, use of hormone replacement therapy, and use of oral contraceptives, and PSA screening for prostate cancer. They also adjusted for BMI and diabetes, which could be considered mediators more than confounders. There is evidence that vegetarians have a lower BMI, lower prevalence of overweight and obesity, and from randomized trials that vegetarian diets can help lose weight. Therefore lower body weight might be on the causal pathway between vegetarian diets and lower cancer risk. The authors reported that the associations were slightly stronger when not adjusted for BMI. This suggest a small part of the association between vegetarian diets may be due to lower weight, however, it seems most of the association is independent of BMI.
“Similarly, there is data suggesting vegetarians have a lower risk of diabetes. It is possible therefore that adjusting for diabetes is an over-adjustment, but it was not described in the main paper whether models without diabetes adjustment were run. It’s also possible that adjusting for diabetes did not materially alter the results, but it would have been interesting to know whether there was any impact on the results of such adjustment, because diabetes is a risk factor for several cancer types and could also be on the causal pathway between vegetarian diets and cancer risk.
What are the implications in the real world? Is there any overspeculation?
“The findings suggest vegetarians and people who don’t eat red and processed meat have a lower risk of several cancer types. Although further studies are needed to provide clarity for some of the less common cancer types, these findings provide further support for dietary recommendations that emphasize higher intakes of whole plant foods, such as whole grains, fruits, vegetables, nuts and legumes and less meat. The authors are quite cautious in their interpretation of the data.”
1 https://pubmed.ncbi.nlm.nih.gov/40499906/; https://pubmed.ncbi.nlm.nih.gov/24898235/
Dr Ian Johnson, Nutrition researcher and Emeritus Fellow, Quadram Institute, said:
“This is an important study, mainly because of its unusual size. By pooling results from several smaller independent studies on meat consumption and various types of vegetarian practice, the authors have been able to accumulate enough cancer cases to explore the effects of such diets on many less common types of cancer. The results indicate that diets lacking meat are associated with reduced risks of several types of cancer, though the authors are careful not to overstate the strength and generality of these associations. Conversely there were increased risks of oesophageal cancer in vegetarians, and of colorectal cancer in vegans. These results seem unexpected and certainly deserving of further investigation. The authors speculate that the increased risks might be due to sub-optimal intakes of micronutrients in participants eating diets low, or in the case of vegans, entirely lacking in animal products. If this possibility can be tested and verified, the risks might be avoidable by use of micronutrient supplements or food fortification.”
Dr Aisling Daly, Lecturer in Nutrition, Oxford Brookes University, said:
“This new research builds on previous knowledge relating to diet-related connections with various cancers, but it is interesting to see the strong differences between types of diets and the different types of cancers, where vegetarian diets appear to be most favourable in most cases. The increased risk for carcinoma of the oesophagus is something to be explored further, however. Interestingly, vegan diets appear to be associated with a higher risk, which may be due to the lack of dairy foods which have been previously known to be protective against certain cancers (e.g. colorectal cancer). However, it is important to note that there is a much smaller sample size for those classified as vegans, and as vegetarians, in comparison with the meat-eaters. Additionally, the study can only identify trends based on the diet type, but it doesn’t do detailed diet analysis so we don’t know if the vegan or vegetarian diets are objectively “healthy” or if they simply omit meat and animal products, or which components of these diets might be playing the key role. The authors recognise this as a limitation to the study, and it is an important limitation to note. Vegetarian diets can usually be more health-promoting than meat-based diets, but if people are not substituting the meat products appropriately, the intended health benefits may not appear. Regardless, this research adds further support for promoting more plant-based eating with lower meat consumption.”
Prof Jules Griffin, Director of the Rowett Institute, University of Aberdeen, said:
“The paper by Dunneram and colleagues is particularly impressive in terms of its size in surveying the relationship between diet and the risk of developing cancer, bringing together studies from across the world to look at over 1.8 million people. They find that vegetarian diets, fish-based and chicken-based diets are associated with lower risks of developing different types of cancer compared with people eating a meat-based diet, adding to the evidence that diet has an important role in cancer risk. However, there was a major surprise in this manuscript that the greatest risk of colon cancer was not associated with red meat consumption, as there is a wealth of evidence that diets high in red and processed meat do increase an individual’s risk of colon cancer – indeed the vegan group had the highest risk which was very surprising! The authors discuss in their paper that this might be because many meat eaters in this study are eating red and processed meat in moderation. What is missing in this study is a comparison to a group eating the NHS Eatwell guidelines, where meat and fish consumption is in moderation, but at the same time provides important nutrients to the diet – this may be the optimum diet for reducing risk in the population for diet associated cancer.”
‘Vegetarian diets and cancer risk: pooled analysis of 1.8 million women and men in nine prospective studies on three continents’ by Yashvee Dunneram et al. was published in the British Journal of Cancer at 01:00 UK time on Friday 27 February 2026.
DOI: 10.1038/s41416-025-03327-4
Declared interests
Dr Michael Jones: “I have no conflicts to declare.”
Prof Tom Sanders: “I was Chair of the British Nutrition Foundation Report on Nutrition and Development: Short and Long term consequences for Health.
I have received grant funding for research on vegans in the past. I have been retired for 10 years but during my career at King’s College London, I formerly acted as consultant for companies that made artificial sweeteners and sugar substitutes.
I am a member of the Programme Advisory Committee of the Malaysia Palm Oil Board which involves the review of research projects proposed by the Malaysia government.
I also used to be a member of the Scientific Advisory Committee of the Global Dairy Platform up until 2015.
I did do some consultancy work on GRAS affirmation of high oleic palm oil for Archer Daniel Midland more than ten years ago.
My research group received oils and fats free of charge from Unilever and Archer Daniel Midland for our Food Standards Agency Research.
I was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain.
Member of the Science Committee British Nutrition Foundation. Honorary Nutritional Director HEART UK.
Before my retirement from King’s College London in 2014, I acted as a consultant to many companies and organisations involved in the manufacture of what are now designated ultraprocessed foods.
I used to be a consultant to the Breakfast Cereals Advisory Board of the Food and Drink Federation.
I used to be a consultant for aspartame more than a decade ago.
When I was doing research at King’ College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks. In reference to previous funding to Tom’s institution: ?4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.”
Dr Dagfinn Aune: “No interests to declare.”
Dr Ian Johnson: “No conflicts of interest. My opinions not necessarily those of the Quadram Institute.”
Dr Aisling Daly: “I have no conflicts of interest to declare. I am an AfN registered public health nutritionist and a Senior Lecturer in Nutrition at Oxford Brookes University.”
Prof Jules Griffin: “I am a consultant for Sitryx, a company specialising in designing drugs to target immunometabolism. The company is looking at drugs for irritable bowel disease and psoriasis.
I have received funding from the European Union to investigate endocrine disrupting chemicals and hold a grant from UK Research and Innovation examining the health benefits of a fish diet.
I hold shares in GlaxoSmithKline and Haleon plc.”
This Roundup was accompanied by an SMC Briefing.