The present prospective study was designed to investigate the association between meat, egg, and dairy product consumption and risk of breast cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC) study cohort. Information concerning diet was collected from 319,826 women during the period 1992 - 2003. During a median follow-up period of 8.8 years, 7,119 breast cancer cases were diagnosed. Multivariate Cox proportional hazard models were used to calculate disease hazard ratios. No consistent overall association was found between risk of breast cancer and consumption of any of the food groups under study. High consumption of processed meat was associated with a modest increase in breast cancer risk in the categorical model (hazard ratio: 1.10; 95% CI: 1.00 - 1.20; highest versus with lowest quintile: P for trend = 0.07). An association of breast cancer risk with butter consumption for premenopausal women was suggested in subgroup analysis (hazard ratio: 1.28; 95% CI: 1.06 - 1.53; highest compared with lowest quintile: P for trend = 0.21). Between-country heterogeneity was found for red meat consumption (Q statistic = 18.03; P = 0.05) and was significantly explained by the proportion of meat cooked at high temperature (P = 0.023). The authors conclude that they had not consistently identified intakes of meat, eggs, or dairy products as risk factors for breast cancer.

The current study was designed to examine the relationship between the intake of meat in general, meat prepared by different cooking methods, and dietary intake of heterocyclic aromatic amines (HCA) with the level of DNA adducts (cancer markers) in the breast tissue of women undergoing breast reduction surgery. Consumption of meat and the associated HCA were determined using a questionnaire in 44 women undergoing reduction mammoplasty. A median DNA adduct level of 18.45 per 109 nucleotides in breast tissue was found to be present; median HCA intake was 40.43 ng/day. The level of DNA adducts in breast tissue was found to be statistically significantly correlated with total HCA intake (r = 0.33, P = 0.03), as well as consumption of fried meat (r = 0.39, P = 0.01), beef (r = 0.32, P = 0.03), and processed meat (r = 0.51, P = 0.0004). However, the detected DNA adducts were not necessarily specific only for HCA, so it is possible that HCA intake reflects intake of other genotoxic substances in meat prepared at high temperatures, such as polycyclic aromatic hydrocarbons.

The current prospective study was designed to examine the relationship between red meat consumption during adolescence and premenopausal breast cancer. A total of 39,268 premenopausal women within the Nurses' Health Study II who completed validated food questionnaires concerning their diets during high school were followed from 1998 to 2005. There were 455 new cases of invasive premenopausal breast cancer in this group between 1998 and 2005. Compared with women in the lowest quintile of red meat consumption during high school, the multivariate-adjusted RR for the highest quintile was 1.34 (95% CI, 0.94-1.89). The association was found to be statistically significant only for hormone receptor–positive tumors (RR, 1.36; 95% CI, 1.08-1.70). The authors conclude that higher red meat consumption during adolescence may increase the risk of premenopausal breast cancer.

The effect of meat consumption on the risk of breast cancer in the UK Women's Cohort Study was evaluated in this study. 35,372 women aged 35 to 69 years between 1995 and 1998 were recruited and their diets were assessed by a 217-item food questionnaire. High intake of meat compared with no meat consumption was found to be associated with premenopausal breast cancer, HR=1.20 (95% CI: 0.86–1.68). Larger effects were found in postmenopausal women for all meat types, with significant correlations with total, processed and red meat consumption. Processed meat had the strongest positive association with postmenopausal breast cancer, with HR=1.64 (95% CI: 1.14–2.37) for high consumption compared with none. The authors conclude that both pre- and postmenopausal women who consumed the most meat had the highest risk of breast cancer.

The current case-control study among members of the Iowa Women's Health Study was designed to assess the potential role of heterocyclic amines and intake of well-done meat on breast cancer risk. Heterocyclic amines formed in meats cooked at high temperatures have been shown to promote mammary cancer in animals. Usual consumption of meat and usual meat preparation practices were determined by a questionnaire which included color photographs showing examples of various levels of doneness of hamburger, steak, and bacon. The study included 273 case subjects and 657 controls. Doneness level of meat and breast cancer risk were found to have a dose-response relationship. The adjusted odds ratios (ORs) for very well-done meat versus rare or medium-done meat were 1.54 (95% confidence interval [CI]=0.96-2.47) for hamburger, 2.21 (CI=1.30-3.77) for beef steak, and 1.64 (CI=0.92-2.93) for bacon. Women who consistently ingested these three meats very well done had a 4.62 times higher risk of breast cancer (CI=1.36-15.70) than women who consumed the meats rare or medium well done. The risk of breast cancer also increased with increasing intake of well-done to very well-done meat. The authors conclude that consumption of well-done meats (and, thereby, exposure to heterocyclic amines or other mutagenic compounds formed as a result of high-temperature cooking) may play a significant role in the risk of breast cancer.

Here, the effects of diet and body weight in 472 women diagnosed with early-stage breast cancer during 1982 to 1984 were studied with respect to eventual breast cancer recurrence and death. The most powerful effects were observed in premenopausal women. It was found that increasing consumption of butter, margarine, and lard (risk ratio (RR)=1.67; 95% confidence interval (CI)=1.17–2.39) and beer (RR=1.58; CI=1.15–2.17) increased the risk of recurrence, after accounting for disease stage and age. An increased risk of recurrence was also found for consumption of red meat, liver, and bacon, corresponding to approximately a doubling of risk for each number of times per day that foods in this category were consumed (RR=1.93; CI=0.89–4.15). Body weight also increased risk at the rate of 9% (RR=1.09; CI=1.02–1.17) for each kg/m2 (equivalent to about 5.8 pounds for a woman 54 inches tall). For risk of death, the results were similar, but relative body weight was more strongly correlated, increasing risk by 12% per kg/m2 (RR=1.12; CI=1.03–1.22).