Energy Balance and Metabolic rate in Active Midlife Women

Abstract

LEARNING OUTCOME: To understand the relationship between energy balance and metabolic rate during rest, sitting, and standing in active midlife women.The metabolic consequences of abnormal eating habits in young women are well documented; however, there is a paucity of data examining this issue in active midlife women. This study examined the relationship between energy balance (EB) and metabolic rate at rest (RMR), sitting, and standing in active (>4 h aerobic activity/wk) midlife women (40–5O yrs). All subjects (n=15) reported being premenopausal, weight stable (>2yr), and completed the Three Factor Eating Questionnaire (TFEQ) (cognitive restraint subscale). Energy intake (El) and energy expenditure (EE) were estimated concurrently using 7-d weighed food and activity records. EB (kcal/d) was determined by subtracting El from EE. Subjects were rank ordered from most negative to least negative EB. The upper tertile (EB=−742 kcal/d; n=5) were classified as having negative (MEG) EB and the upper tertile (EB=−130 kcal/d; n=5) were classified as adequate (ADQ) EB. Metabolic rate was measured twice after a 12-h fast at the same time during the menstrual cycle and 20–24 h after the last exercise bout. NEG and ADQ subgroups were similar in age, body weight, body fat, fat-free-mass (FFM), restrained eating scores, and EE, but differed (P<0.01) in El (NEG=1465 kcal/d; ADQ=2026 kcal/d). There were no differences between the groups in metabolic rate at rest, sitting, or standing while controlling for FFM. Thus, for these active women, negative EB did not affect metabolic rate. Using all subjects, there was no correlation between restrained eating scores and EB (r=0.21, P=0.44) or El and EB (r=0.30, P=0.27). Thus, the TFEQ was not a good discriminator for determining restrictive eating behaviors in these women. Finally, actual RMR was compared to predicted RMR using the Harris-Benedict equation. Results showed that this equation predicted the actual RMR to within 38 kcal/d for all subjects. Supported by the Gatorade Sports Science Institute Student Research Grant.