Woman's True Caloric Needs
March 26, 2003
How many calories does it really take
to see healthy, moderately active women through an average day? A recent study
by scientists at the Agricultural Research Service's
Children's Nutrition Research Center
in Houston, Texas, set out to determine the actual energy requirements of
healthy underweight, normal-weight and overweight women of reproductive age.
Led by Nancy F. Butte, an energy metabolism expert, the study's ultimate
objective will be to define the precise energy requirements of pregnant and
lactating women, to best ensure good health for mothers and infants.
Researchers used what's called the doubly labeled water method to measure
total energy expenditure (TEE) in 116 women living in urban areas. This method
is a way to measure energy expenditure and energy requirements of free-living
individuals. Doubly labeled water, or heavy water, is a safe, non-radioactive
form of water enriched with heavier forms of hydrogen and oxygen that are used
to track end products of metabolism, water and carbon dioxide.
Volunteers followed their usual diet and activity regimens. Thirteen of them
had low body mass index (BMI), 70 had normal ones and 33 had high BMIs. The BMI
is the ratio of weight to height squared and is used to gauge body fat in
adults. A multi-component model was used to measure body fat.
Researchers measured the volunteers' 24-hour basal metabolic rate (BMR) and
energy expenditure in a special room called a respiration calorimeter. They
calculated physical activity levels by dividing volunteers' total energy
expenditure, or TEE value, by their BMR values.
The study showed that current suggested daily caloric intakes for healthy
women of childbearing age living in industrialized societies need to be
revised, based on women's BMIs. Low-, normal- and high-BMI groups used varying
amounts of energy, ranging from about 2,100 to 2,700 calories--8.9 to 11.5
megajoules--per day. A joule is a measure of work or energy. The findings were
published in the March issue of the American
Journal of Clinical Nutrition.
ARS is the
U.S. Department of Agriculture's chief
scientific research agency.