There is no clear definition of low-carbohydrate diets (LCDs). What LCDs have in common, however, is that they restrict the intake of carbohydrates relative to standard recommended diets. Breast milk is the best form of nutrition for newborns and infants. This study reports two cases of women who followed a LCD while breastfeeding. The breast milk sample collected from patient 1 eighteen days after the introduction of a LCD had a fat content of 2.7 g/dL, whereas the breast milk sample collected from the patient fifty days after the introduction of the diet had a fat content of 2.9 g/dL. Both the samples had a protein content of 1.3 g/dL and a carbohydrate content of 7.9 g/dL. The breast milk sample collected from patient 2 had a fat content of 3.5 g/dL, protein content of 1.9 g/dL, carbohydrate content of 8.2 g/dL and calorie content of 73 kcal/dL. The samples of breast milk collected from patients on a LCD contained higher protein levels. Breastfeeding women are particularly at risk of the negative consequences of dietary mistakes.