Longitudinal changes in the physical activity of adolescents with anorexia nervosa and their influence on body composition and leptin serum levels after recovery

Abstract

Objective: Patients with anorexia nervosa (AN) are often observed to have high levels of physical activity, which do not necessarily diminish after a successful therapy. Previous studies have shown that body fat tissue recovery in these patients is associated with a disproportional restoration of the adipocyte hormone, leptin. Therefore, we wondered whether the individual variation in physical activity in AN patients prior to treatment may be related to body fat percentage and plasma leptin level outcome.

Method: Body fat percentage, leptin serum, and physical activity levels (accelerometer) were measured in adolescents with an (n=37, age 13 to 17.5 years) at initial assessment, at the end of study participation (median 12 months), and at one-year follow-up.

Results: Accelerometer data were used to split the patients in two groups: those with low (n=26) and those with high levels of physical activity (HLPA, n=11). These groups did not differ in terms of age, IQ, presence of menses, BMI and season of admission. The HLPA group was characterized by a longer total duration of illness. Physical activity levels during therapy decreased for the group with initially HLPA and increased for the group with low levels of physical activity (to comparable levels). Physical activity remained stable after one year. The increase in body fat percentage and leptin levels were dependent on the recovery status; however, recovered patients with initially HLPA had significantly higher fat mass during the follow-up.

Discussion: HLPA, an important modulator of AN progression in adolescents, can be successfully diminished by therapeutic intervention. Among recovered patients, those with initially HLPA had higher fat mass levels than those with low levels of physical activity. This finding suggests that HLPA are an important modulator of the body composition recovery mechanism.

Figure 1. Timeframe of the study.

The diagram shows the number of patients in the study at each data measurement point between enrolment, initial assessment (T0), and maximal duration of treatment (T12).

Figure 2. Characterization of LLPA and HLPA patients.

A) Duration of illness, defined as time between obtaining the first diagnosis and initial assessment at Rintveld clinic. Duration of illness is significantly higher for the HLPA (high levels of physical activity) group than for the LLPA (low levels of physical activity) group. Mean±SEM, Student’s t-test, * P<.05. B) Physical activity of the LLPA and the HLPA groups at initial assessment, at the end of study, and at follow-up. Data are expressed as mean ± SEM; Repeated measures ANOVA, Student’s t-test as a post hoc test: *** P<.001 in comparison to the LLPA group at the same time point.

Figure 3. Differences between recovered and non-recovered LLPA and HLPA patients.

Daily physical activity scores (A), fat% (B), leptin serum levels (C), and ghrelin serum levels (D) plotted for recovered and non-recovered LLPA and HLPA groups at 3 time points (initial assess. = initial assessment). Data are expressed as mean ± SEM; Two-way ANOVA, Student’s t-test as a post hoc test: * P<.05, *** P<.001 between the recovered (Rec) and non-recovered (nonRec) patients in the same group (LLPA or HLPA) and at the same time point; ## P<.01, ### P<.001 between the LLPA and the HLPA groups at the same time point. Numbers within bars indicate sample size per group.