You hear a lot about a “plant-based diet” for lower cancer risk. But what does that mean? Is a vegetarian diet the key for lowest risk?
A massive study that followed more than 472,000 people in the UK for over a decade provides new evidence to address this question.
The New Study: Meat-Eating Habits and Cancer Risk
Based on their responses to an eating habits questionnaire, people ages 40 to 70 without any history of cancer were classified as follows:
- Regular meat-eaters who reported eating processed meat, red meat (beef, pork, lamb) or poultry more than five times a week.
- Low meat-eaters who reported consuming processed meat, red meat and/or poultry five or fewer times a week.
- Fish-eaters who reported that they never consumed red meat, processed meat or poultry but ate fish.
- Vegetarians who said they never consumed any meat, poultry or fish.
More than 11 years after people reported their eating habits, researchers found that low meat-eaters, fish-eaters and vegetarians were all less likely to have developed cancer than people classified as regular meat-eaters. Looking specifically at some of today’s most common cancers:
Colorectal cancer was clearly lower in low meat-eaters compared to regular meat-eaters. There was also a trend for lower risk in fish-eaters and vegetarians, but the difference was not statistically significant. This could be because the far smaller number of fish-eaters and vegetarians made it hard to see a significant difference or could be because of the wide variation in other influences on risk of this cancer within these groups.
Post-menopausal breast cancer was slightly lower in low meat-eaters and fish-eaters than in regular meat-eaters, but only among vegetarians was a lower risk statistically significant. (That means the association was unlikely to have occurred by chance.) Further analysis showed that the lower risk among vegetarians was strongly associated with having a lower BMI (body mass index, a way of assessing weight).
Prostate cancer occurred less in fish-eater and vegetarian men than in regular meat-eaters. However, it may be that other lifestyle and health behaviors (for example, use of prostate cancer screening) accounted for this difference, rather than diet. No difference in risk of this cancer was seen between regular meat-eaters and low meat-eaters.
AICR Blueprint to Beat Cancer
The AICR Cancer Prevention Recommendations highlight important choices to build a lifestyle that can reduce your risk of cancer. And if these AICR Recommendations are like a blueprint for a whole building, the results of this study demonstrate a good fit for one room in that building.
The “low meat-eaters” in this UK study probably had eating habits that aligned well with the AICR Recommendation to limit red meat to no more than 12 to 18 ounces per week. If portions of meat were about three ounces (the size of a deck of cards), eating no more than five servings per week would mean people in this group were eating no more than 15 ounces a week. And in this study, poultry consumption was counted in those servings, too. So red meat may even have been at the low end of AICR’s recommended maximum for red meat.
AICR’s Third Expert Report shows that colorectal cancer risk climbs even faster with consumption of processed meats (like hot dogs, sausage and bacon) than with unprocessed beef, pork and lamb. In this UK study, we don’t know how much of the meat consumed by regular meat-eaters or by low meat-eaters was processed meat.
But here’s a crucial point about how findings from this new study fit in the context of AICR’s Cancer Prevention Recommendations and analysis of overall research. Limiting red and processed meat is one part of the overall plant-focused eating pattern in AICR’s Recommendations—not the only focus.
Study Findings in Context
Analysis in the UK study adjusted for a variety of risk factors and lifestyle choices (including physical activity, alcohol and smoking) that could be associated with cancer risk. Even after that adjustment, the links between diets that included less meat and lower cancer risk still stood.
However, the researchers who conducted the study note that the lower risk of cancer in groups with less meat or no meat consumption may still reflect other differences in lifestyle choices between these groups.
Although differences in consumption of meat, poultry and fish may play important influences on cancer risk, current research suggests that the overall dietary pattern overrides the influence of any single food group or nutrient. For example, even in eating habits that limit or avoid meat:
- Vegetables and fruits provide a vast array of nutrients and natural plant compounds that seem to support antioxidant defenses and cell signaling pathways that keep cells off a pathway that leads to cancer. Yet it’s interesting that in the UK study, adding an adjustment for reported vegetable and fruit consumption did not change any of the associations between meat consumption categories and cancer risk.
- Whole grains and legumes (like dry beans, lentils and soyfoods) supply different nutrients and phytochemicals than you get from vegetables and fruits. And they’re important sources of dietary fiber, which is strongly linked with lower risk of colorectal cancer. The UK study did not ask about these foods. Some people in the groups eating little or no meat may have been eating high-fiber diets with plenty of whole grains. But even among those who avoided meat, some may have relied on low-fiber refined grains, missing out on a diet as protective as possible.
- Foods that promote weight gain—like sugar-sweetened beverages, sweets, French fries and other deep-fried fast foods—are highlighted in the AICR Recommendations as foods to limit. That’s not because of any evidence supporting a direct effect of these foods on cancer risk. But research shows that they often lead to unintended weight gain. This can raise body fat to levels that trigger hormonal changes and inflammation that promote cancer development. The UK study focused on meat consumption and did not look at people’s consumption of these other foods.
When the UK study researchers adjusted results for BMI, associations between the meat consumption-based group and risk of overall cancer, colorectal cancer and prostate cancer changed little, if at all. However, the association of vegetarian eating with lower risk of post-menopausal breast cancer disappeared. Statistical analysis led study authors to suggest that the vegetarian diet’s association with lower risk of this cancer may have been due to an influence on weight.
However, regardless of people’s weight at the beginning of the study, each of the groups categorized based on meat consumption could include people who maintained their weight and those whose weight increased substantially over the years. Differences in weight gain among people in the study could also add a layer of fuzziness to the picture of diet’s association with cancer risk.
Take-Home Message on Meats in Your Diet
The UK study adds important insights to research and recommendations about a plant-based diet to lower cancer risk.
- A variety of eating patterns that limited or avoided meat were associated with lower risk of cancer compared with people who ate larger amounts of meat (likely beyond AICR’s Recommended maximum). And this was seen for some of the most common forms of cancer.
- But defining eating habits based only on meat consumption misses important differences in what people eat—both in health-protecting foods and in foods more concentrated in calories than nutrients. And it doesn’t account for lifestyle choices like physical activity and alcohol that are also powerful influences on cancer risk.
Stick with the AICR Recommendations as your blueprint for building a lifestyle. Creating eating habits that avoid overeating meat and fit your preferences and lifestyle is a great place to start. Just don’t stop there. Each step you take closer to the blueprint brings you closer to lower risk of cancer and better overall health.