Lactation ketoacidosis is a very rare cause of metabolic acidosis in breastfeeding patients. We present a case of a 34-year-old female, 8-weeks postpartum, who was breastfeeding while also on the ketogenic diet. She developed dyspnea, chest pain, nausea, vomiting, and an inability to tolerate oral intake for several days. She presented with a metabolic acidosis with an anion gap of 33, HCO3 of 5.1 mmol/L, venous pH of 7.045, and serum b-hydroxybutyrate of 7.4 mmol/L. She was treated in the emergency department with intravenous normal saline and intravenous dextrose, with prompt transfer to the intensive care unit for treatment with an intravenous sodium bicarbonate drip and an intravenous insulin drip with dextrose. After normalization of laboratory values, she re-developed an elevated anion gap acidosis after breastfeeding in the ICU overnight. She was started on a carbohydrate-rich diet and made a full recovery without reported repeat incidences. We provide a summary of our case, discuss known causes of lactation ketoacidosis, and emphasize the importance of a thorough history and physical. In this case a dietary history was more helpful than a very expensive laboratory and imaging evaluation.