Researchers have compiled data from more than 1.8 million people in a new large analysis on diet and cancer, published in the British Journal of Cancer.
Participants came from several countries, particularly the United States and the United Kingdom. They were followed for an average of 16 years.
In the studies, researchers compared several types of diets. These included vegetarians, vegans, people who eat fish, and people who eat poultry.
The results showed differences between the groups. People who eat fish had a lower risk of breast cancer, kidney cancer, and colorectal cancer.
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People who mainly eat poultry had a lower risk of prostate cancer, according to the analysis.
Experts warn results are not definitive
Senior researcher Paula Berstad from the Cancer Registry at the Norwegian Institute of Public Health emphasizes that the results do not provide clear answers.
She points out that previous research reviews from organizations including the WHO and the World Cancer Research Fund have not found strong links between diet and many types of cancer.
There are also differences in how participants reported their diets.
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The studies used different questionnaires, and among the many meat eaters there was considerable variation in how much meat they actually consumed.
The researchers behind the analysis also write that conducting many statistical analyses can increase the risk of random results. Therefore, the conclusions should be interpreted with caution.
The most important conclusion
One of the more surprising findings was that a vegan diet in the analysis was associated with a higher risk of colorectal cancer.
The researchers point to lower intake of calcium and other nutrients as a possible explanation.
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At the same time, the analysis found no difference between vegetarians and meat eaters in terms of the risk of colorectal cancer.
This surprises researchers because previous research has linked red and processed meat to this particular form of cancer.
Overall, however, the study suggests that a properly composed vegetarian dietary pattern may be associated with a lower risk of several types of cancer, although the results should be interpreted with caution.
Sources: Forskning.no, British Journal of Cancer, WHO, and World Cancer Research Fund.
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