One reason people gain weight is eating more calories from food than what they need for
energy over 24 hours. Metabolism is the amount of energy a person uses over 24 hours.
Researchers want to study the relationship between changes in metabolism and how much a
To see how much food a person eats when the body's temperature is cooled. To study how
changes in metabolism may alter the amount of food a person eats.
Healthy people ages 18-55.
Participants will stay at NIH for 20 days.
During the first 4 days, participants will have:
- Medical exam
- Blood and urine tests. One blood test includes drinking a sugar solution.
- DXA body composition scan
- Questions about foods they like, physical activity, and personal behavior
- Exercise test on a stationary bicycle
Participants will spend 24-hour periods in a metabolic chamber. The chamber will be at normal
room temperature or cooler.
Some times, participants will eat a diet that matches their daily needs. Other times, they
can eat as much as they wish from a vending machine.
Participants will have blood and urine collected.
Participants will swallow an ingestible wireless sensor and wear a small data recorder
On the second to last day, participants will stay in the metabolic chamber but only consume
water and non-caffeinated sugar-free beverages.
Participants will come back for 1-day visits at six months and one year from the first
admission. They will have blood and urine tests, and a DXA scan. They will answer questions
on physical activity and food habits.
This study, conducted at the NIH Clinical Research Unit at the Phoenix Indian Medical Center,
will examine how the body s metabolism (energy expenditure) changes when people overeat and
when they fast and how different diets (e.g., high-protein or high-fat) affect metabolism.
The results may provide information about whether there are mechanisms that make some people
more resistant than others to gaining weight when they eat more.
Non-smoking healthy subjects between 18 and 55 years of age who weigh no more than 350 pounds
may be eligible for this study. Participants undergo the following procedures:
- Pregnancy test for women of childbearing age.
- Oral glucose tolerance test. For this test, an I.V. line (needle attached to a plastic
tube) is inserted into a vein to allow several blood draws without repeated needle
sticks. After the first blood sample is drawn, the subject drinks a cola-flavored sugar
solution. Five additional blood samples are then drawn over 3 hours.
- Blood test for DNA (genetic) studies related to obesity, diabetes and related medical
- DEXA scan. This test measures body fat. The subject lies on a table while a very small
dose of X-rays is passed through the body.
- Respiratory chamber. This test measures how many calories the body burns a day and
assesses energy balance between intake and expenditure. Subjects stay in a room with two
windows, equipped with a sink, toilet, television and DVD player, desk, chair, telephone
and bed for 24 hours. The test is repeated five times during the first 18-day admission
and 3 times during the second 13-day admission. For the first two sessions, subjects are
fed a diet equal to the amount of energy their body uses. For the next 6 stays they are
fed double the amount of calories their body usually uses for 5 of the stays and fast
(consume nothing but water and soda without caffeine or calories) during 1 stay. The
overfeeding diets may be high or low in protein, normal in protein, or high in fat.
Blood tests are done on the day of each respiratory chamber session and a 24-hour urine
sample is collected for one day while in the chamber.
- Eating behavior questionnaires.
- Psychological performance tests.
Some participants are asked to volunteer to repeat two of the chamber studies to validate the
measurements. The repeat session includes only the fasting and the overfeeding with normal
All participants are followed at 6 months with blood tests, a DEXA scan, and urine tests
(including pregnancy test for women). At annual visits for years 1 through 7, participants
have the 6-month tests plus an oral glucose tolerance test.