Patients scheduled for bariatric surgery are instructed to stick to a low calorie, protein sparing diet for a brief period before their operation. However, too low calorie intake can lead to starvation ketoacidosis. We describe a case of a patient who rigorously restricted oral calorie input, even more than prescribed. Immediately after surgery, a marked metabolic acidosis was noted. This ketoacidosis was successfully treated with oral glucose substitution. A superposed respiratory acidosis could have had detrimental effects.