Evidence that the
insulin pathway may be involved in breast
carcinogenesis has increased the interest in dietary factors that influence insulin secretion and resistance. We investigated
dietary carbohydrate, fibre, glycaemic index (GI) and glycaemic load (GL) in a prospective study of 324 breast
cancers diagnosed in 12,273 post-menopausal women. Although an increase of 1 standard deviation in
carbohydrate was marginally associated with risk of
breast cancer, relative risk (RR) 1.31 (95% CI, 0.98, 1.75), there were no significant associations with fibre, 1.08 (0.92, 1.26), GI, 0.98 (0.88, 1.10) or GL, 1.19 (0.93, 1.52) or with
carbohydrate foods (bread, rice, pasta). The RR for
carbohydrate and localized disease was elevated, 1.40 (1.02, 1.92), but like those for fibre, GI and GL did not differ significantly between localized and non-localized disease. RRs for grade I, but not grade II or III, tumours were elevated for fibre, 1.38 (1.08, 1.75),
carbohydrate, 1.56 (1.08, 2.25) and GL, 1.41 (1.01, 1.98) but not for GI, 0.84 (0.65, 1.09). The RRs for fibre and oestrogen receptor (ER) positive (+) and
progesterone receptor (PR) positive (+) tumours, 1.36 (1.10, 1.67), differed significantly from those for ER positive (+) and PR negative (-) tumours, 1.01 (0.61, 1.69) and ER-/PR- tumours, 0.65 (0.43, 0.99), p = 0.005. Our data do not support a strong role for GI and GL in breast
carcinogenesis but suggest that increased intake of fibre and
carbohydrate may be associated with the diagnosis of
cancers of more favourable prognosis.