Reprinted from Eating Disorders Review
May/June 2007 Volume 18, Number 3
©2007 Gürze Books
Women with the female athlete triad often restrict their food intake in an attempt to achieve an ideal body weight or shape, and/or to improve their athletic performance.
Weight loss is only one of the many physiological effects that follow food restriction. A cascade of metabolic shifts also occurs as the body attempts to conserve energy, including a decrease in resting energy expenditure (REE), and changes in metabolic hormone concentrations, including triiothyronine (T3), insulin-like factor, and ghrelin.
Drive for thinness scale
Drive for thinness (DT), a subscale of the Eating Disorder Inventory (EDI), is a self-report measure of disordered eating attitudes about body image, weight, and shape. DT consists of perceptual, behavioral, and attitudinal parts, and is probably triggered when there is a discrepancy between actual and ideal body weight that exceeds the specific idealized preference of cultural thinness and involves body image dissatisfaction. In exercising women, disordered eating attitudes (which can be reflected by a high DT score) may contribute to behavioral changes leading to conscious restriction of food intake and or excessive exercise, potentially ending in the female athlete triad. Interestingly, differences in body weight between amenorrheic and eumenorrheic exercising women are often not seen, which suggests that endocrine and metabolic adaptations to conserve energy and reduce weight loss should be closely examined to better understand the physiology of the triad.
A ‘proxy indicator’of energy deficits
Researchers at the University of Toronto and Penn State University report that the DT score may serve as a “proxy indicator” of underlying energy deficiency and thus may be useful for identifying women at risk for the female athlete triad (Appetite 2007; 48:359).
Dr. Mary Jane De Souza and her colleagues evaluated psychometric and metabolic factors in 9 sedentary volunteers and 43 exercising women using a combination of psychological and physiological tests. Dr. De Souza and other researchers used a large observational study over 2 to 3 months to examine the relationships between physical activity, metabolism, and reproductive function. Body composition, REE, and total body mass were measured, as was dietary energy intake. Energy intake was assessed from 3-day nutritional logs recorded for two weekdays and one weekend day during each week of REE determination. Volunteers also kept daily activity logs, and recorded their heart rates immediately after finishing 3 minutes or more of continuous physical activity.
Subjects took the entire EDI and the Three Factor Eating Questionnaire, a 51-item questionnaire that measures 3 dimensions of human eating behavior: dietary cognitive restraint, disinhibition, and hunger. Blood samples were collected between 7:30 and 10 a.m. during the early follicular phase of the menstrual cycle for menstruating exercising and sedentary volunteers. For amenorrheic and oligomenorrheic volunteers, blood samples were collected during the first 6 days of each 30-day monitoring period.
Exercise was defined as “sedentary” when purposeful exercise was less than 2 hours per week and “exercising” when purposeful exercise included more than 2 hours per week. A normal DT score was defined as less than or equal to 6 (and about 75% of college women have scores in this range). DT was defined as higher than normal when the score was 7 or greater.
This was the first study designed to evaluate whether the DT subscale of the EDI, used in conjunction with other EDI scores, can detect individual with signs of chronic energy deficiency. The authors’ findings indicate that a clinical classification of high DT is significantly associated with reduced REE and hormonal indicators of compensatory adaptations to energy deficiency, and therefore can establish a link between this measure and the physiological base of the female athlete triad.
The average measured REE of the high-DT group was 86% of predicted and is consistent with the clinical use of REE to assess metabolic status in anorexic women (a reduced REE of 60% to 80% is often reported in clinical models of starvation, such as AN, during period of low body weight, and prior to refeeding). The percentage of individuals who would be clinically classified as energy deficient was 66% in the group with an extra-high DT score and 27% in the normal DT score groups.
Other hormonal indicators verified energy deficiency
Finding that a reduced REE is associated with a high DT score was reinforced by other hormonal indicators of energy deficiency. It is likely that the low T3-like syndrome seen in the high- DT group played a role in the energy-conserving reduction in REE. T3 levels were 17.7% lower than those reported in the exercising normal DT group and 26.6% lower than that observed in the sedentary normal DT group.
Ghrelin, an orexigenic gut-related peptide, is believed to be a primary peripheral metabolic signal for hunger, eating, and energy homeostasis. In this study, the authors found ghrelin levels were significantly elevated in the exercising women with a high DT score, indicating an adaptation to energy deficiency in these women.
According to the authors, future studies should be designed to test the efficacy of DT to identify individuals with energy deficiency and concomitant menstrual disturbances. A strong association between elevated DT scores and signs of energy deficiency in exercising women with subtle menstrual disturbances such as late luteal phase defects and anovulation might be very useful because it could lead to an intervention before more severe and obvious problems such as amenorrhea and oligomenorrhea develop.
The authors also note that the EDI is cost-effective, noninvasive, and easy to administer and interpret. However, the use of the DT scores needs to be studied in larger groups before the efficacy for using it in a single individual can be proved.