Higher protein intake, particularly protein from animal sources, is associated with a modest but lower risk of breast cancer recurrence and death, regardless of insulin receptor status.
Using information gathered through biennial questionnaires from 6,348 women who were diagnosed with stage I to III breast cancer between 1976 and 2004, investigators found a significant inverse association between total protein intake and distant breast cancer recurrence (P = .02). This association was driven specifically by protein from animal sources (P = .003) rather than vegetable sources.
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Pathology records were reviewed and histology samples were analyzed for insulin receptor and estrogen receptor expression. Associations between breast cancer recurrence and protein intake, amino acids, or protein-containing food groups did not differ by tumor receptor status or body mass index at time of cancer diagnosis. Given that the association between protein intake and recurrence was not confined to tumors expressing insulin receptors, “It is difficult to invoke the insulin pathway as a mechanism to explain these findings,” the investigators wrote.
Given the only “modest survival advantage” of higher protein intake among women with breast cancer, and given the “challenges involved in randomized trials of diet, this association is unlikely to ever be definitively tested in a randomized trial,” Dr. Holmes and her associates wrote.
“However, the modest survival advantage with higher protein intake has been found in several studies, and we feel it is important that patients with breast cancer and their clinicians know this. At the least, it may provide reassurance that consuming protein-containing foods is not likely to increase the risk of breast cancer recurrence,” the researchers concluded.
This study was sponsored by grants from the National Institutes of Health. Dr. Holmes and one other investigator reported receiving financial compensation from Bayer HealthCare Pharmaceuticals.
jcraig@frontlinemedcom.com
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