Experiments have shown that some artificial sweeteners like those in diet soda can cause changes in how the body responds to and uses sugar. These changes increase the chance of obesity, type 2 diabetes mellitus, and other metabolic diseases. In this study, the investigators plan to see if the most commonly used artificial sweetener, aspartame, affects the body's response to sugar. The investigators believe that if metabolic changes are observed in a person who consumes aspartame, then removing all aspartame from the diet might lead to a reversal of the changes and a normalization of test results.~The investigators plan to study two (2) cohorts of healthy volunteers: 1) Those who regularly drink at least three cans per day of diet soda that contains aspartame (Cohort 1, Aspartame Consumers) and 2) participants who consume less than or equal to two (2) cans of diet soda per week (Cohort 2, Aspartame Naïve Participants).~Phase I of the study, the investigators will ask participants questions about their usual diet, including how much diet soda they usually drink. Participants will be screened by a test called the oral glucose tolerance test, or OGTT. This test involves coming to the hospital to drink sugary syrup, then have blood sugar checked every thirty (30) minutes for five (5) hours. Before the test, participants must refrain from eating or drinking anything for ten (10) hours. If the OGTT shows a high value, then the participant in cohort 1 (Aspartame Consumers) who regularly drink 3 or more cans per day of diet soda will be approached about continuing into the second phase of the study. For the participants in cohort 2 (consume less than or equal to two (2) cans of diet soda per week; Aspartame Naïve Participants), this will be the end of their participation in the study.~Phase II of the study, blood tests, OGTT, stool samples, and weight and body fat measurements a few times a week will track any changes in the participants during the study. During the phase II five (5) week study, participants will receive all of their meals from the Rockefeller University Hospital and should not have any outside food or drinks. The diet used throughout this study phase (II) is the Prudent Metabolic Diet. Participants can leave the hospital and continue to work, but must come for all tests and to receive meals. During Week One, participants will eat only food provided by the hospital but will continue to drink three (3) cans of diet soda per day. In Weeks Two through Four, participants will continue to eat food given to them by the hospital and will not be allowed to consume any foods or drinks that contain aspartame. In Week Five, participants will continue on the hospital diet, but will again start drinking three (3) cans of diet soda per day.
Experiments have shown that some artificial sweeteners like those in diet soda can cause changes in how the body responds to and uses sugar. These changes increase the chance of obesity, type 2 diabetes, and other metabolic diseases. In this study, the investigators plan to see if the most common artificial sweetener, aspartame (brand name Equal, NutraSweet), causes these changes. The investigators believe that if metabolic changes are observed in a person who consumes aspartame, then removing all aspartame from the diet might lead to a reversal of the changes and a normalization of test results.This would impact sweetener additives in our foods and thus decrease the incidence of obesity, diabetes, and the metabolic syndrome.