The United Nations recommends that women consume ≥5 food groups, also known as the minimum dietary diversity score for women (MDD-W), for nutritional health. This is increasingly unattainable for populations in climate hot zones coping with food insecurity by prioritizing calories over dietary breadth. Breastfeeding mothers may be particularly vulnerable to adverse health impacts of low dietary diversity due to elevated nutritional requirements for lactation. We investigated how the protective effects of MDD-W for folate adequacy varies by MDD-W score and mother-infant life history characteristics. We conducted a secondary analysis of cross-sectional data from breastfeeding mothers (n = 228) in northern Kenya, surveyed during the 2006 Horn-of-Africa drought. Logistic regression models for adequate dietary folate (and vitamins B12 and B6) and normal homocysteine (folate-replete status) evaluated the effect of MDD-W alone and in interaction with infant/maternal characteristics. MDD-W (as ordinal or dichotomous variable) was positively associated with adequate folate (and vitamin B12). Having male infant was inversely associated with adequate dietary folate. MDD-W was generally unassociated with homocysteine. However, there was an interaction between MDD-W and sex of the infant. Namely, MDD-W ≥ 3 predicted increased probability of normal homocysteine among mothers with female infants but not male infants. Diets consisting of three or more food groups may protect adequate folate intake for many breastfeeding mothers. More research is needed to establish what level of dietary diversity would protect against hyperhomocysteinemia during breastfeeding and what factors promote or hinder the benefit of diversified diets on maternal folate nutrition.