Breast milk samples from 12 lactating women with bariatric surgery were investigated by comparing the macronutrient and energy content with samples from 36 non-surgical controls. Samples were analyzed with the Human Milk Analyzer and the maternal diet 24 h prior to sampling with a food record. A higher fat, energy, and a slightly higher carbohydrate milk content was found in the surgical group compared to the non-surgical group (3.0 ± 0.7 versus 2.2 ± 0.9 g/100 ml, P = 0.008; 61.0 ± 7.2 versus 51.7 ± 9 kcal/100 ml, P = 0.002; and 6.6 ± 0.6 versus 6.3 ± 0.4 g/100 ml, P = 0.045, respectively). No correlations and no strong explanatory variance were found between milk macronutrient composition and corresponding maternal dietary intake. The nutritional value of breast milk after bariatric surgery appears to be at least as high as in non-surgical controls.