Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/19/2002
Publication Date: 3/24/2003
Citation: BUTTE, N.F., TREUTH, M.S., MEHTA, N.R., WONG, W.W., HOPKINSON, J., SMITH, O.E. ENERGY REQUIREMENTS OF WOMEN OF REPRODUCTIVE AGE. AMERICAN JOURNAL OF CLINICAL NUTRITION. 2003. v. 77. p. 630-638. Interpretive Summary: We wanted to determine the energy requirements of underweight, normal-weight, and overweight women of reproductive age. We used the doubly labeled water method to estimate the energy requirements of women grouped by low-, normal-, and high-body mass index, based on an equation involving the total energy expenditure (TEE) of these women. We determined their TEE by various methods, including room respiration calorimetry, and we calculated their physical activity level and expenditure under various circumstances. We derived each subject's body composition from a model including the person's total body water, body volume and bone mineral content. We assessed the subject's fitness with a cycle test, measuring their maximum oxygen levels, and we did blood tests. Our results showed that energy requirements differed among the three groups of women. Differences in energy expenditure among the groups were accounted for by fat mass and fat-free mass. Major predictors of basal metabolic rate, 24-hour energy expenditure, and TEE were weight, height and body composition, while fitness and fasting metabolic profile played only minor roles. The mean physical activity level of these women indicated that the multiples of basal metabolic rate that have been used to estimate the energy requirements of moderately active women have been underestimated. We conclude that current dietary recommendations of energy intake of moderately active women need to be increased based on TEE. Current recommendations for energy intake of women don't accurately account for what women of different weights and sizes expend in terms of physical activity. The doubly labeled water method we used, which employed stable isotopes in measurements taken over several days, properly assessed and accounted for those factors. This is a landmark study that contributes key findings to our knowledge of women's energy requirements, and if implemented, will improve standards for the appropriate assessment, treatment, and health of women.
Technical Abstract: Background: Energy requirements of women have been based upon total energy expenditure (TEE) derived from the factorial approach or as multiples of basal metabolic rate (BMR). Objective: This study was designed to reevaluate the energy requirements of healthy underweight, normal-weight and overweight women of reproductive age based on TEE by the doubly labeled water (DLW) method. Design: Energy requirements of 116 women (n=13 low-BMI, n=70 normal-BMI and n=33 high-BMI) were estimated from TEE measured by the DLW method. 24-h EE and BMR were measured by room respiration calorimetry; activity energy expenditure (AEE) and physical activity level (PAL) were calculated as TEE-BMR and TEE/BMR, respectively. Body composition was derived from a multicomponent model based on total body water, body volume and bone mineral content. Fitness was assessed by a cycle O2max test, strength by weights and physical activity by questionnaire. Fasting serum chemistries were measured by standard techniques. Results: Energy requirements differed (P=0.001) among the low-BMI (8.9 ± 0.9 MJ/d), normal-BMI (10.1 ± 1.4 MJ/d), and high-BMI (11.5 ± 1.9 MJ/d) groups. Major predictors of BMR, 24-h EE, and TEE were weight, height and body composition, with minor contributions of fasting metabolic profile and fitness. Fat-free mass (FFM) and fat mass (FM) accounted for differences in EE seen between BMI groups. Mean PAL of 1.86 of these women suggests that multiples of BMR used to estimate energy requirements of moderately active women have been underestimated.