Well-done, grilled red meat increases the risk of colorectal adenomas

Red meat or meat-cooking methods such as frying and doneness level have bee n associated with an increased risk of colorectal and other cancers. It is unclear whether it is red meat intake or the way it is cooked that is invol ved in the etiology of colorectal cancer. To address this issue, we develop ed an extensive food frequency questionnaire module that collects informati on on meat-cooking techniques as well as the level of doneness for individu al meat items and used it in a study of colorectal adenomas, known precurso rs of colorectal cancer. A case-control study of colorectal adenomas was co nducted at the National Naval Medical Center (Bethesda, MD) between April 1 994 and September 1996. All cases (n = 146) were diagnosed with colorectal adenomas at sigmoidoscopy or colonoscopy and histologically confirmed. Cont rols (n = 228) were screened with sigmoidoscopy and found not to have color ectal adenomas. The subjects completed a food frequency questionnaire and a nswered detailed questions on meat-cooking practices. We used frequency and portion size to estimate grams of meat consumed per day for total meat as well as for meat subgroups defined by cooking methods and doneness levels. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using logistic regression, adjusted for age, gender, total caloric intake, reason for screening (routine or other), and several established risk factors for colorectal adenomas or cancer, including the use of nonsteroidal anti-infl ammatory drugs, physical activity, and pack-gears of cigarette smoking. The re was an increased risk of 11% per 10 g/day (or 2.5 oz/week) of reported r ed meat consumption (OR, 1.11; CI, 1.03-1.19). The increased risk was mainl y associated with well-done/very well-done red meat, with an excess risk of 29% per 10 g/day (OR, 1.29; CI, 1.08-1.54) versus an excess of 10% per 10 g/day (OR, 1.10; CI, 0.96-1.26) for consumption of rare/medium red meat. Hi gh-temperature cooking methods were also associated with increased risk; 26 % per 10 g/day (OR, 1.26; CI, 1.06-1.50) of grilled red meat and 15% per 10 g/day (OR, 1.15; CI, 0.97-1.36) of pan-fried red meat consumption. There w as an increased risk of colorectal adenomas associated with higher intake o f red meat, most of which was due to the subgroup of red meat that was cook ed until well done/very well done and/or by high-temperature cooking techni ques, such as grilling. These results are consistent with the hypothesis th at carcinogenic compounds formed by high-temperature cooking techniques, su ch as heterocyclic amines and polycyclic aromatic hydrocarbons, may contrib ute to the risk of developing colorectal tumors.