The findings, which take data from the United Kingdom Women's Cohort Study, suggest a reduced risk of distal colon cancer in red meat free diets though numbers with this outcome were small.
“The impact of different types of red meat and dietary patterns on cancer locations is one of the biggest challenges in the study of diet and colorectal cancer,” said Dr Diego Rada Fernandez de Jauregui, lead study author and member of the Nutritional Epidemiology Group at the University of Leeds.
“While further analysis in a larger study is needed, it could provide valuable information for those with family history of colorectal cancer and those working on prevention."
Colorectal cancer (CRC) is the second most commonly diagnosed cancer in women and the third in men worldwide.
Carcinogenic claims
In 2015, the International Agency for Research on Cancer (IARC) classed red meat as “probably carcinogenic to humans” and processed meat as “carcinogenic to humans”.
Recent research carried out in September 2017 by the World Cancer Research Fund (WCRF) and American Institute for Cancer Research (AICR) could not confidently arrive at any firm conclusions due to limited evidence on dietary patterns and CRC.
In Dr de Jauregui’s analysis, 32,147 women were recruited and surveyed between 1995 and 1998. They were monitored for a mean time period of 17.2 years.
In addition to reporting their dietary habits, the team also explored the relationship between the four dietary patterns (red meat, poultry, fish and vegetarian) and colorectal cancer.
A total of 462 incident CRC cases were documented; 335 colon cancers (172 proximal and 119 distal) and 152 in the rectum.
Despite a link between red meat consumption and distal colon cancer rates, further analysis found no evidence of a reduction in risk of overall CRC, colon cancer or rectal cancer when comparing grouped red meat free diets with diets containing red meat.
“Our results are not statistically significant for red meat eating dietary patterns and overall risk of CRC, however, a red meat‐free diet was significantly protective against distal colon cancer,” the study said.
“This is of interest from a public health point of view as in this cohort, a red meat eating pattern characterized by lower overall meat intakes, may be generally at lower risk of colorectal cancers compared to populations with a higher meat consumption.”
NOCs and bacon flavour
In trying to explain the link, the team pointed to compounds either present in red meat or formed during its cooking that could increase CRC risk.
These included animal fat, haem iron, heterocyclic amines (HCAs) and the formation of N‐nitroso compounds (NOCs), compounds that are found in cured meat and contribute to the "bacon flavour".
However, a study comparing high (more than 130 g per day) and low/medium red and processed meat consumption (less than 130 g per day) on CRC did not find a significant risk reduction for the risk of CRC.
The study also took into account fish consumption as one of the dietary patterns that may exert a degree of protection against CRC.
The team commented that women adhering to a Mediterranean dietary pattern that was also low in red meat might have a lower risk of CRC, especially rectal cancer.
“Risk estimates for rectal cancer, showed a weak protective association in the case of fish‐eaters and vegetarians, with a null association in the poultry eaters group. However, none of the results reached statistical significance.”
Source: International Journal of Cancer
Published online ahead of print: DOI: 10.1002/ijc.31362
“Common dietary patterns and risk of cancers of the colon and rectum: Analysis from the United Kingdom Women's Cohort Study (UKWCS).”
Authors: Diego Rada-Fernandez de Jauregui, Charlotte E.L. Evans, Petra Jones, Darren C. Greenwood, Neil Hancock, Janet E. Cade