Red meat refers to the flesh obtained from cows, pigs and lambs, that is, beef, pork and lamb/mutton respectively. These contain more of the muscle protein called myoglobin which carries oxygen to the muscle tissue, similar to hemoglobin in the blood. The presence of myoglobin contributes to the red color. Processed red meats also contain a high sodium content, and other factors like nitrates and nitrites, which may break down into carcinogenic molecules after consumption.
While eating red meat has at various times been considered as a risk factor in the causation of breast cancer, data has been lacking to validate this hypothesis.