The Pennington Biomedical Research Center is looking for healthy, lean or slightly overweight volunteers to participate in a two year research study testing the effects of diet on healthy aging.

The study has three levels of participation. You will first have to successfully complete 3 screening visits, which will be done at Pennington's outpatient clinic. Once you have completed the screening phase, then you will be asked to complete the baseline testing. Baseline testing involves 4 outpatient clinic visits and a 2 night, 2 1/2 day stay on the inpatient unit. Following successful completion of the baseline testing period, you will be enrolled in the two-year CALERIE Study.

Some volunteers will eat breakfast and dinner meals at the Pennington Center with lunch and weekend meals packed to go for a 27-day period, followed by two years of following a prescribed diet at home. In addition, some participants will receive dietary counseling while all participants will receive free medical evaluations.

Participants will be asked to do one of the following:

1. Follow a reduced calorie diet.

2. Follow a standard diet.

After you are enrolled in the study, you will be asked to come to the center for follow-up evaluations at Months 1, 3, 9, 12, 18 and 24. Most of these evaluations will be done in the outpatient clinic, however for some of the testing you will be required to stay 1-2 nights at the Pennington Center's inpatient unit. Volunteers will go through various testing.

To qualify, volunteers must be:
* Lean to Slightly Overweight, 22-27.9 BMI (BMI Calculator)
* Non-smoker
* Non-diabetic
* On no medications (birth control, ok)

* Ages: Female 21-47, Male 21-50

* Weight stable

* Generally Healthy