This study aimed to document whether food insecurity was associated with beliefs and attitudes towards exclusive breastfeeding (EBF) among urban Kenyan women. We conducted structured interviews with 75 human immunodeficiency virus (HIV)-affected and 75 HIV-status unknown, low-income women who were either pregnant or with a child ≤24 months and residing in Nakuru, Kenya to generate categorical and open-ended responses on knowledge, attitudes and beliefs towards EBF and food insecurity. We facilitated six focus group discussions (FGD) with HIV-affected and HIV-status unknown mothers (n = 50 women) to assess barriers and facilitators to EBF. Of 148 women with complete interview data, 77% were moderately or severely food insecure (FIS). Women in FIS households had significantly greater odds of believing that breast milk would be insufficient for 6 months [odds ratio (OR), 2.6; 95% confidence interval (95% CI), 1.0, 6.8], that women who EBF for 6 months would experience health or social problems (OR, 2.7; 95% CI, 1.0, 7.3), that women need adequate food to support EBF for 6 months (OR, 2.6; 95% CI, 1.0, 6.7) and that they themselves would be unable to follow a counsellor's advice to EBF for 6 months (OR, 3.2; 95% CI, 1.3, 8.3). Qualitative analysis of interview and FGD transcripts indicated that the maternal experience of hunger contributes to perceived milk insufficiency, anxiety about infant hunger and a perception that access to adequate food is necessary for successful breastfeeding. The lived experience of food insecurity among a sample of low-income, commonly FIS, urban Kenyan women reduces their capacity to implement at least one key recommended infant feeding practices, that of EBF for 6 months.