The Effects of Bariatric Surgeries on Glucose Metabolism

Inclusion Criteria:

* Hypoglycemic RYGB patients with documented blood glucose level \<50 mg/dl
* Asymptomatic individuals with bariatric surgery
* Healthy non-surgical patients with no personal history of diabetes
* Subjects must physically be able to come to our clinical research center Cedars-Sinai Medical Center

Exclusion Criteria:

* Active heart, lung, liver, gastrointestinal or kidney disease; unable to give informed consent; pregnancy; uncontrolled high blood pressure or high cholesterol; significant anemia (hemoglobin \<11g/dL); prisoners or institutionalized individuals; type 2 diabetes mellitis; development of any serious medical or psychiatric illness during recruitment or studies;
* RYGB patients will be disqualified if they have gastric outlet obstruction or severe diarrhea.
* Healthy non-surgical patients with personal history of diabetes

For administration of atropine, the following exclusions also apply:

* History of glaucoma
* Uncontrolled hypertension (any subjects with BP\>140/90 and history of dyslipidemia
* Taking any medication that might interact with atropine and cannot be stopped will be excluded from the study)
* Myasthenia gravis
* Brain pathology
* Enlarged prostate in men