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The room calorimeter: Atwater's "copper box" revisited.

The study of nutrition owes a great deal to the year W.O. Atwater spent in Carl Voit's lab in Germany. Voit's pioneering work focused on respiration-the exchange of gases between the blood and tissues--and calorimetry--the measurement of heat. It was Voit who had taken the first steps toward quantifying the human body's nutritional needs.

Atwater returned to America inspired. Before long he built a room calorimeter for human studies, as well as a bomb calorimeter for systematically measuring the energy values in foods themselves. The bomb calorimeter enabled Atwater to burn foods and products of excretion--human input and output, so to speak-making it possible to calculate the body's energy expenditure as the difference.

The room calorimeter revealed precise measurements about human energy expenditure. Early versions were slightly claustrophobic copper-lined chambers. In them, college students pedaled stationary bicycles, studied, and performed other physical and mental chores.

Just outside the little temperature-controlled room, Atwater and his associates were hard at work, keeping meticulous notes about the students' metabolism and recording the quantity of energy the volunteers expended on each task.

Atwater's calorimeter was capable of a precision almost unheard of in those days. When, in the middle of the night, a study volunteer happened to adjust his watch, the calorimeter duly indicated the sudden rise and fail in room temperature.

With accuracy like that, it's not surprising that Atwater's old mentors back in Europe pricked up their ears. Soon, eminent nutrition scientists like Carl Voit were factoring Atwater's baseline information into their experiments.

The famous Atwater 4, 9, 4 values were, until quite recently, linchpins in the study of nutrition. Atwater determined that one gram of carbohydrate yields 4 calories of energy, while fat yields 9 and protein 4, in a mixed diet.

Today, the room calorimeter continues to be a USDA research mainstay. Volunteers at the Human Nutrition Research Center in Beltsville, Maryland, lead comparatively normal lives inside the 9- by 10- by 8-foot chamber, eating, exercising, and resting. Meanwhile, as in the old days, scientists carefully monitor their bodily functions.

The data generated with these volunteers may help researchers develop recommendations for diet and physical activity. Or it may trace the metabolism of individual nutrients, measuring the fat/lean composition of human bodies and assessing how people respond to differences in their diet, such as the proportion of fat.

Beltsville's room calorimeter uses two types of calorimetry: direct, which measures heat emission, and indirect, which calculates energy expenditure from measurements of oxygen consumption and carbon dioxide production. For accuracy's sake, the two methods can be checked against each other.

But not all calorimeters are room-sized. A tiny, specially modified indirect calorimeter at the ARS Children's Human Nutrition Research Center in Houston, Texas, accommodates the smallest of newborn babies.

While still in the hospital, these preterm infants have their first "volunteer" experience. They are placed in a full-body, custom-designed preemie calorimeter that resembles a newborn isolette. Every calorie of energy the newborns burn is recorded by researchers.

While in the calorimeter, babies continue to receive expert medical care without interruption.

Babies who have completed lull terms of gestation and who are between 3 and 6 months of age are studied during sleeping periods. They snooze for short times under specially designed calorimeter hoods. Sound asleep, the infants enable scientists to estimate the comparative energy expenditures of full-term infants.

Pregnant women, including teenage mothers-to-be, participate in room calorimeter studies in Houston. They're helping scientists answer important questions such as:

* How many calories do normal, healthy pregnant women consume? What about teenage moms? Infants?

* How do nutritional factors contribute to a normal pregnancy?

* What would constitute proper RDA's for pregnant women?

* How do breast-fed babies metabolize nutrients? Does it differ from formula-fed infant patterns?

* What nutrients are lacking in baby formula?

By addressing such basic questions about human nutritional needs, calorimeter studies touch many lives, including those of America's poorest and most dependent citizens. Both USDA's Food Stamp and WIC (Women and Infant Children) programs are predicated on a cogent understanding of human dietary needs--an understanding obtained from state-of-the-art scientific measurement and study.
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Title Annotation:Wilbur Olin Atwater
Author:Wiggen, Jeanne
Publication:Agricultural Research
Date:Jun 1, 1993
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