In a new population study, scientists have found more evidence that consuming a lot of meat might not be a good idea, though the association between meat and cancer depends on multiple factors [1].
Diet and health
Given that lifestyle changes may be the only anti-aging intervention available today, it is important to elucidate the effects that diets have on health. Unfortunately, this is made harder by the variability of dietary habits and numerous other confounding factors. Because it is relatively costly (but possible) to conduct a proper clinical trial of a diet, researchers often make do with data drawn from larger projects. Thankfully, the information in such databases has become more and more abundant.
UK Biobank is a huge repository of various health data gathered over several years from almost half a million people between the ages of 40 and 70. This data bank is a treasure trove for geroscientists, and it has been featured in our articles more than once. This time, a group of researchers used UK Biobank to find correlations between diet and cancer.
The study encompassed all 472,377 UK Biobank participants who were free from cancer at recruitment. The participants were categorized as regular meat-eaters (52.4%), low meat eaters (43.5%), fish-eaters (2.3%), and vegetarians (almost 2%). The vegetarian group also included 446 vegans, and the average follow-up period was 11.4?years. The researchers assessed the relationship between those dietary habits and the risk of all types of cancer, colorectal cancer, postmenopausal breast cancer, and prostate cancer.
We already know that some connection between diet and cancer exists: due to a growing body of evidence, WHO now considers processed meat to be a proven carcinogen and red meat to be a likely one. A recent study has also found direct evidence in the form of a genetic mutational signature of red meat in colorectal tumors [2].
In population studies, adjusting for possible confounding variables is key. For instance, in one study, the strong correlation between meat consumption and all-cause mortality became statistically insignificant after adjusting for alcohol consumption and smoking [3], while another study found that BMI (body mass index) explains most of the correlation between meat consumption [4].
In this new study, the researchers accounted for multiple potentially important variables, including age, BMI, physical activity, socioeconomic status, education, smoking, alcohol consumption, and diabetes.
Less than straightforward
Compared with regular meat-eaters, being a low meat-eater, fish-eater, or vegetarian were all associated with a slight reduction of overall cancer risk (2%, 10%, and 14%, respectively), but this association was even stronger for smokers and statistically insignificant for non-smokers.
Being a low meat-eater was associated with a 9% lower risk of colorectal cancer in comparison to regular meat-eaters; however, significant sex differences emerged. In men, the risk of colorectal cancer in low meat-eaters, fish-eaters, and vegetarians was significantly reduced compared to regular meat-eaters (by 11%, 29% and 43%, respectively), while in women, the effect became statistically insignificant.
In another interesting finding, vegetarian postmenopausal women had a 12% lower risk of breast cancer, but the relationship stopped being statistically significant after accounting for BMI. For other cancers, the effect of BMI was minuscule.
Another drastic effect was recoded in men: being a fish-eater or a vegetarian was associated with a 20% and 31% lower risk of prostate cancer, respectively.
Variables and more variables
Still, it is virtually impossible to account for all possible factors, and the researchers list many caveats. For instance, they admit that they were unable to adjust for total energy intake because no such question was asked at recruitment. Given how potent caloric restriction has been proven in mitigating health risks, this overlooked factor might be an important one.
As in some other similar studies, no distinction was made between vegetarians and vegans, although this could be relevant as well: evidence exists that a higher intake of dairy products may increase the risk of prostate cancer [5].
Finally, not all meats are the same: other recent studies have shown that red meat, especially processed meat, is significantly less healthy than poultry.
Conclusion
As in many other population studies, this one answers some questions but also raises new ones. Among the notable takeaways is that there are too few vegetarians, especially vegans, in the population for a robust analysis, even when using such humongous databases as UK Biobank. Still, the study seems to confirm at least one previously established association: consuming a lot of meat appears to be harmful in the long run.
Literature
[1] Watling, C. Z., Schmidt, J. A., Dunneram, Y., Tong, T. Y., Kelly, R. K., Knuppel, A., … & Perez-Cornago, A. (2022). Risk of cancer in regular and low meat-eaters, fish-eaters, and vegetarians: a prospective analysis of UK Biobank participants. BMC medicine, 20(1), 1-13.
[2] Gurjao, C., Zhong, R., Haruki, K., Li, Y. Y., Spurr, L. F., Lee-Six, H., … & Giannakis, M. (2021). Discovery and features of an alkylating signature in colorectal cancer. Cancer discovery, 11(10), 2446-2455.
[3] Mihrshahi, S., Ding, D., Gale, J., Allman-Farinelli, M., Banks, E., & Bauman, A. E. (2017). Vegetarian diet and all-cause mortality: Evidence from a large population-based Australian cohort-the 45 and Up Study. Preventive medicine, 97, 1-7.
[4] Papier, K., Appleby, P. N., Fensom, G. K., Knuppel, A., Perez-Cornago, A., Schmidt, J. A., … & Key, T. J. (2019). Vegetarian diets and risk of hospitalisation or death with diabetes in British adults: results from the EPIC-Oxford Study. Nutrition & diabetes, 9(1), 1-8.
[5] Clinton, S. K., Giovannucci, E. L., & Hursting, S. D. (2020). The world cancer research fund/American institute for cancer research third expert report on diet, nutrition, physical activity, and cancer: impact and future directions. The Journal of nutrition, 150(4), 663-671.
