January 16, 2025 from Medscape
A growing body of research supports what nutrition experts have suspected for years: eating more plant-based foods is associated with a lower risk for several major cancers. While early studies focused on vegan and vegetarian diets, newer research has turned toward broader patterns that emphasize—but don’t require—plant dominance.
A study published in Nature Microbiology compared the microbiomes of over 21,000 vegans, vegetarians, and omnivores and found that those who ate more plant-based foods had fewer microbes linked to colon cancer. The benefits weren’t exclusive to vegans—omnivores who incorporated more plant foods also showed healthier microbiome profiles, suggesting the protective effect lies more in the quantity of plants than strict dietary labels.
“More plants, less cancer,”
said Nigel Brockton, PhD, vice president of research at the American Institute for Cancer Research (AICR).
What Counts as a Plant-Based Diet?
The definition of a plant-based diet can vary widely. Experts caution that the term is more of a spectrum than a checklist. Elizabeth A. Platz, ScD, professor of cancer epidemiology at Johns Hopkins Bloomberg School of Public Health clarified that a plant-based diet is an umbrella term, covering many different diet patterns.
The AICR’s “New American Plate” promotes a flexible framework: two-thirds of the plate should include vegetables, fruits, whole grains, and beans, with the remaining third composed of animal protein. This approach aligns with a “plant-forward” model, where plants form the dietary base, regardless of whether someone is fully vegan or vegetarian.
Carrie Daniel-MacDougall, PhD, MPH, of MD Anderson Cancer Center, explained that
“It doesn’t have to be entirely vegan or vegetarian. It just means you’re eating more plants than anything else.”
Which Cancers See the Greatest Risk Reduction?
Recent studies highlight several cancer types where plant-based diets appear most beneficial:
- Digestive system cancers: 18–32% reduced risk
- Pancreatic cancer: up to 32% reduced risk
- Prostate cancer: 13% reduced risk
- Breast cancer: 9% reduced risk
A 2023 meta-analysis of 22 cohort studies with nearly 58,000 participants found a 12% overall cancer risk reduction with higher adherence to plant-based diets. The risk dropped 14% when the diet focused on whole, unprocessed plant foods. Conversely, unhealthful plant-based diets—high in processed snacks or sugary foods—were associated with a 7% increased cancer risk.
Gender and regional differences also emerged. In a meta-analysis of vegetarian diets and gastrointestinal cancers, men experienced a 43% risk reduction while women did not. Asian populations saw greater benefits than North Americans, suggesting cultural and dietary context plays a role.
Why Do Plant-Based Diets Help?
Experts agree that plant-based eating helps prevent cancer through multiple mechanisms. These diets are typically lower in calories and saturated fat and higher in fiber, all of which promote healthy weight maintenance—an important factor since obesity is a known cancer risk.
“Probably in the next 10 years, obesity will overtake smoking as the predominant risk factor for cancer,”
said Brockton.
Fiber-rich diets also support blood sugar control, reduce inflammation, and encourage a more diverse microbiome—all key players in cancer prevention. Brockton noted that people with higher fiber intake tend to respond better to certain cancer treatments like immunotherapy.
“The microbiome has an impact on the immune system. They’re even showing that people with higher fiber intakes have better responses to immunotherapy in melanoma.”
Diets high in processed meats and red meat increase cancer risk due to compounds like nitrates and heme iron, which contribute to oxidative stress and inflammation. Plant-based diets, on the other hand, provide anti-inflammatory and antioxidant compounds that counter these effects.
Food Quality Still Matters
Not all plant-based diets are created equal. Eating fries and sugary cereals every day still qualifies as plant-based, but not as healthy.
Edward Giovannucci, MD, of Harvard T.H. Chan School of Public Health emphasized the importance of distinguishing an overall plant-based diet from a healthy plant-based diet.
Healthy plant-based diets emphasize whole grains, fruits, vegetables, nuts, legumes, and healthy oils. They minimize ultra-processed foods, sweetened beverages, and refined grains.
How to Talk to Patients About Diet
For healthcare providers, advising patients on diet doesn’t require a complete overhaul. Asking what a patient typically eats for breakfast, lunch, and dinner can be a helpful starting point. From there, clinicians can recommend simple changes such as choosing whole grains or doubling up on vegetables at meals.
Daniel-MacDougall commented that
“While you’re working on [increasing fiber], you’re going to increase your plant foods by default. But it’s also going to help you identify plant foods that are higher quality and less refined.”
Platz recommends gradual shifts over radical changes. Even replacing half of a meat portion with a second vegetable serving can be a step in the right direction.
Remembering the Importance of Plants in Diets
Plant-based diets, particularly those rich in whole, minimally processed foods, are increasingly associated with reduced cancer risk—especially for digestive, breast, prostate, and pancreatic cancers. While more research is needed to refine the definitions and mechanisms, the message is clear: eating more plants is one of the most evidence-based strategies for long-term cancer prevention.
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