Cancer

Vegans have the lowest overall cancer risk

By WhyStopHarmingAnimals.com

Of the diet groups researchers compare (meat-eaters, fish-eaters, vegetarians and vegans), vegans have the lowest overall cancer risk[1][2][3]. The result comes up in several recent papers: an analysis of plant-based dietary patterns and total cancer risk in the American Journal of Clinical Nutrition[1], a separate analysis of vegan diets and total cancer incidence[2], and a 2026 meta-analysis in the European Journal of Epidemiology[3]. Each put the vegan pattern at the bottom of the risk table[1][2][3].

A British Journal of Cancer paper went cancer by cancer[4]. For all five cancer types it examined, the vegan pattern had the lowest risk[4].

The cohorts behind the result

Two long-running cohorts carry much of the weight. The Adventist Health Study-2 tracked cancer among 69,120 Seventh-day Adventists. Vegans had 16% less cancer overall than non-vegetarians and 34% less of the female-specific cancers[5]. Vegetarians as a whole had 8% less cancer overall and 24% less cancer of the gastrointestinal tract[5].

In Britain, researchers pooled two cohorts totalling 61,647 people[6], who developed 4,998 cancers between them. Vegetarians, 2,246 of them vegan, had 12% less cancer at all sites combined, 63% less stomach cancer and 77% less multiple myeloma[6]. Colorectal cancer was the exception in that analysis: it was no lower in vegetarians[6].

The digestive system shows the clearest pattern across studies. A 2022 meta-analysis covering 3,059,009 people found plant-based eating came with 18% lower risk of digestive-system cancers in the pooled cohorts and 30% lower in the case-control studies[7], with pancreatic and colorectal cancer carrying the clearest signals[7]. A 2025 review of seventeen substitution studies[8], which model what happens when animal foods or animal protein are replaced with plant foods[8], found lower colorectal and breast cancer risk in six of them and no difference in four, alongside lower cancer and all-cause mortality[8].

Red and processed meat, and colorectal cancer in particular, have their own long record, including the World Health Organization cancer agency's classification of processed meat as a human carcinogen. That evidence is covered separately.

Dairy and eggs

Cutting out meat removes one set of risks. Vegans also skip dairy and eggs, and both have signals of their own.

A 2022 meta-analysis of 34 cohorts, covering 3,171,186 people and 88,545 deaths, found high milk intake came with 10% higher cancer mortality in women, and 17% higher for whole-fat milk[9]. Deaths from liver cancer rose 13%, from ovarian cancer 32% and from prostate cancer 23%[9]. Fermented milk went the other way in women[9].

For prostate cancer, a 2015 analysis of 32 studies found total dairy came with 7% higher risk per 400 g a day[10], and milk and dairy calcium tracked the same way[10]. Calcium from supplements or from non-dairy sources did not[10]. If the mineral were the problem, the pills would show the same rise, so the finding points at the dairy itself[10]. The ovarian picture is more mixed[11]: a 2020 analysis of 29 studies linked whole milk to higher ovarian cancer risk, while low-fat milk, dietary calcium and vitamin D tracked with lower risk in the same paper[11].

The egg signal is smaller[12]. Across 13 studies, eating eggs came with about 4% higher breast cancer risk overall and about 10% higher at two to five eggs a week[12]. A meta-analysis of 12 studies, covering 629,453 people and 3,728 cases, found high egg intake came with 21% higher ovarian cancer risk[13]. That result reached significance in the case-control studies and fell just short in the cohorts[13]. The effects are modest, but breast and ovarian cancer are common enough that modest effects add up to a lot of women[12].

Why the numbers might fall this way

Part of the answer is what meat brings. Heme iron, the pigment that makes red meat red[14], tracks with colon cancer: across prospective cohorts of 566,607 people, colon cancer risk was 18% higher at the highest heme-iron intakes than at the lowest[14].

Part may be hormonal. IGF-1 is a growth factor that promotes cell growth, and high levels are linked with higher risk of some cancers. Among 696 men, the 233 vegans had 9% lower IGF-1 than meat-eaters and vegetarians[15].

After a diagnosis

Most of this evidence is about who gets cancer. A smaller body of work asks what diet does once someone already has it, and the best of it concerns prostate cancer.

Among 2,062 men with prostate cancer, those who ate the most plant foods after diagnosis had 47% less disease progression, according to a 2024 study in JAMA Network Open[16]. Among men with Gleason 7 or higher, a healthy plant-based score came with 55% less progression[16].

Ornish's trial randomized 93 men with early prostate cancer who had declined conventional treatment[17]. In the lifestyle group, on a vegan diet with exercise and stress management, PSA fell 4% over the first year while it rose 6% in usual care, and no one needed treatment that year, against six men in the control group[17]. By two years, 27% of the usual-care group had gone on to surgery, radiation or androgen deprivation, compared with 5% of the lifestyle group[18]. There were no deaths in either group[18]. These endpoints measure progression and treatment, not survival, and the diet came bundled with exercise and stress management[17].

The one survival result comes from a study of 32 women with breast cancer[19]. At five years, about 50% of the control group had died, against about 10% of the vegan group, a roughly fivefold gap[19]. With a sample that small, chance can produce large differences, so this is a signal worth testing in a larger study rather than a settled result[19]. None of it argues for skipping treatment. Diet belongs alongside an oncologist's care.

What the evidence can and cannot say

Nearly all of this is observational. People who choose vegan diets may differ in other ways, and although the cohorts adjust for smoking, alcohol, weight and exercise, some confounding can remain. The British cohorts found no colorectal advantage for vegetarians[6]. Low-fat milk tracked with lower ovarian risk in one analysis[11]. The egg results are small[12].

What holds across the Adventist, British and meta-analytic data is the direction[1][2][3][5][6]. When researchers line up the diet groups, the one that eats no animal products has the fewest cancers overall[1][2][3], and the animal foods it leaves out (processed and red meat, whole milk, eggs) are the ones that keep turning up on the wrong side of the ledger[9][11][12][13][14].