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Findings of studies on the link between dietary acid-base balance and bone mass are relatively mixed. We examined the association between dietary acid-base balance and bone mineral density (BMD) in a sample of Iranian women, hypothesizing that a higher dietary acidity would be inversely associated with BMD, even when dietary calcium intake is adequate. In this cross-sectional study, lumbar spine and femoral neck BMDs of 151 postmenopausal women aged 50 - 85 years were measured using dual-energy x-ray absorptiometry. Dietary intakes were assessed using a validated food frequency questionnaire. Renal net acid excretion (RNAE), an estimate of acid-base balance, was then calculated indirectly from the diet using the formulae of Remer (based on dietary intakes of protein, phosphorus, potassium, and magnesium; RNAERemer) and Frassetto (based on dietary intakes of protein and potassium; RNAEFrassetto), and was energy adjusted by the residual method. After adjusting for potential confounders, multivariable adjusted means of the lumbar spine BMD of women in the highest tertiles of RNAERemerand RNAEFrassettowere significantly lower than those in the lowest tertiles (for RNAERemer: mean difference -0.084 g/cm2; P=0.007 and for RNAEFrassetto: mean difference - 0.088 g/cm2; P=0.004). Similar results were observed in a subgroup analysis of subjects with dietary calcium intake of >800 mg/day. In conclusion, a higher RNAE (i. e. more dietary acidity), which is associated with greater intake of acid-generating foods and lower intake of alkali-generating foods, may be involved in deteriorating the bone health of postmenopausal Iranian women, even in the context of adequate dietary calcium intake.