The rate of successful breastfeeding (BF) establishment beyond hospital discharge in women with type two diabetes (T2DM) is poorly described, although small studies suggest it is reduced compared to both women with gestational diabetes (GDM) and women without diabetes. One postulated reason is delayed secretory activation (SA), which is the onset of copious milk production, or milk ‘coming in’, that normally occurs between 24 and 72 hours postpartum. SA can be measured by examining changes in milk constituents that occur at the time copious milk secretion begins, including citrate and lactose whose concentrations rapidly increase. We examined the change in breastmilk citrate concentration in women with T2DM, control women matched for age-, body mass index (BMI)-and parity, and control women matched for age and parity but with normal BMI (18.5-25). Women with T2DM had a delay in SA, compared to both BMI-matched and normal BMI controls. This was manifest by a slower rise in citrate and a lower mean plateau value, both results suggesting early breastmilk volume may be lower in women with T2DM. Higher insulin dose per/kg in women with T2DM was associated with increased time to predetermined citrate values and provides further evidence for the role of insulin resistance in impaired milk production. Exclusive breastfeeding at four months postpartum was lower in both women with T2DM and BMI-matched controls; however, it remains unclear to what extent delayed SA (and potential supplemental feeding) influence successful establishment of breastfeeding in women with T2DM and/or higher BMI.