Preoperative fasting is the practice of a surgical patient abstaining from eating or drinking ("nothing by mouth") for some time before having an operation. This is intended to prevent stomach contents from getting into the windpipe and lungs (known as a pulmonary aspiration) while the patient is under general anesthesia.[1] The latest guidelines do not support preoperative fasting, as there is no difference in residual gastric fluid volume, pH or gastric emptying rate following semi-solid meals or drinks, whether in obese or lean individuals.[2][failed verification – see discussion]