Background Ketoacidosis is a severe metabolic complication mainly reported in diabetic patients. Therapeutic fasting is a millennial worldwide practice, believed to improve a large panel of health conditions, but its efficiency and safety profile have not yet been established. We report here a case of euglycemic ketoacidosis in a non-diabetic woman. Case description A 51-year-old woman without a history of excessive alcohol use or medical history, except for a depressive disorder, was admitted in the emergency room for altered general status, deep asthenia, muscular weakness, articular pain, nausea, vomiting, and consciousness disorders. She was practicing during the previous 48 h a therapeutic fasting following a progressive restrictive diet for 4 d. She was diagnosed with ketoacidosis and hospitalized in the intensive care unit. Her laboratory test results indicated pH 7.28, bicarbonate 7 mmol/L, significant ketone bodies, glycemia 8.9 mmol/L without glycosuria, and negative blood alcohol assessment. Glycated hemoglobin was 5.5%, and blood glucose never went above 9 mmol/L. Serum concentrations of free fatty acids were high at 1.13 mmol/L (normal range: 0.13–0.45). Plasma insulin and peptide C were in the normal ranges. Comprehensive plasma and urinary biochemistry panels, including energetic substrates, and chromatography of amino acids and organic acids did not indicate any energetic or metabolic deficiency. The ketoacidosis regressed, and the overall outcome was favorable after intravenous glucose infusion for 48 h, without insulin requirement. Conclusions This report is the first case, to our knowledge, of euglycemic ketoacidosis thought to be induced by therapeutic fasting in a non-diabetic patient. Practitioners should be aware of this complication of fasting.< Réduire