Basal metabolism in women with obesity and anorexia nervosa

Resting Energy Expenditure in Anorexia Nervosa: Measured versus Estimated

Introduction. Aim of this study was to compare the resting energy expenditure (REE) measured by the Douglas bag method with the REE estimated with the FitMate method, the Harris-Benedict equation, and the Müller et al. equation for individuals with BMI < 18.5 kg/m(2) in a severe group of underweight patients with anorexia nervosa (AN). Methods. 15 subjects with AN participated in the study. The Douglas bag method and the FitMate method were used to measure REE and the dual energy X-ray absorptiometry to assess body composition after one day of refeeding. Results. FitMate method and the Müller et al. equation gave an accurate REE estimation, while the Harris-Benedict equation overestimated the REE when compared with the Douglas bag method. Conclusion. The data support the use of the FitMate method and the Müller et al. equation, but not the Harris-Benedict equation, to estimate REE in AN patients after short-term refeeding.

Heart rate variability as a measure of autonomic nervous system function in anorexia nervosa

BACKGROUND AND HYPOTHESIS

Alteration in sympathovagal balance may be a mechanism of increased cardiovascular mortality and sudden death of patients with anorexia nervosa. This study was undertaken to characterize cardiac autonomic control in patients with anorexia nervosa by means of heart rate variability analysis.

METHODS

Heart period variability by 24-h Holter recording was evaluated in 13 young women with anorexia nervosa, 10 constitutionally thin women, and 10 women of normal weight.

RESULTS

High-frequency power, a measure of parasympathetic modulation of heart rate, and all-time domain measures of heart rate variability were higher in patients with anorexia nervosa than in thin women and in those of normal weight. Thin women showed lower values of total power and of most components of power spectrum.

CONCLUSIONS

Our data demonstrate an increased vagal tone in young women with anorexia nervosa. The marked increase in parasympathetic activity, not in response to an increase in sympathetic activity, could be detrimental and may contribute to the higher cardiovascular mortality of these patients.

Basal metabolic rate in anorexia nervosa: relation to body composition and leptin concentrations

BACKGROUND

Leptin is thought to represent a peripheral signal involved in the regulation of energy balance. Its action has been studied in animals and obese subjects. Little is known about leptin's role during negative energy balance.

OBJECTIVE

The objective was to evaluate the relation between energy turnover, body composition, and plasma leptin concentrations in anorexia nervosa (AN).

DESIGN

Sixteen weight-stable women with AN were compared with 22 control subjects and 14 rehabilitated AN patients (R-AN). Basal metabolic rate (BMR) was measured by indirect calorimetry; fat-free mass (FFM) and fat mass (FM) were calculated according to a 4-compartment model. Plasma leptin was determined by radioimmunoassay.

RESULTS

The BMR of AN patients (2.73 +/- 0.37 kJ/min) was significantly lower than that of control subjects (3.45 +/- 0.34 kJ/min) (P < 0.001), even after adjustment for FFM (2.92 +/- 0.33 kJ/min in AN patients and 3.30 +/- 0.26 kJ/min in control subjects; P < 0.004). Plasma leptin concentrations in AN patients were 76% lower than in control subjects, even after body fat was controlled for. In R-AN patients, BMR was not significantly different from that of control subjects and leptin concentrations were generally close to normal. Plasma leptin concentrations correlated significantly with FM (r(2) = 0.53, P < 0.0000) and BMR, even after adjustment for FFM (r(2) = 0.21, P < 0.0003).

CONCLUSIONS

BMR and plasma leptin concentrations are depressed in patients with AN; this is not explained by body-composition changes. The relation between leptin and BMR suggests that leptin plays a role in the energy sparing response to exposure to chronic energy deficiency. The return of BMR to normal and the significant increase in leptin concentrations in R-AN patients suggests a full reversibility of this adaptation mechanism.

The influence of physical activity on BMR

In addition to factors such as fat free mass, hormonal status, genetics and energy balance, previous physical activity has been shown to influence energy turnover during resting (RMR = resting metabolic rate) or basal conditions (BMR = basal metabolic rate). This article presents data on BMR from elite endurance athletes (4 female and 4 male), at least 39 h after their last training session, in comparison with sedentary nonathletic controls matched for sex and fat free mass (FFM). Comparisons with theoretical calculations of BMR were also made. The athletes were shown to have a significantly higher BMR than was expected from calculations based on body mass (16%, P < 0.05) or body composition (12%, P < 0.05). There were no corresponding differences found in the nonathletic control group. The athletes had a 13% higher (P < 0.001) BMR than controls if related to FFM and 16% (P = 0.001) if related to both FFM and fat mass (FM). The athletes were also found to have 10% lower R-values (P < 0.01) indicating higher fat oxidation. The conformity of these findings with the present literature and the possible mechanisms behind them as well as its influence on theoretical calculations of energy turnover (ET) based on activity factors expressed as multiples of RMR are further discussed.

Basal metabolic rate, fat-free mass, and body cell mass during energy restriction

Basal metabolic rate (BMR) has been reported to decrease during semistarvation and during hypocaloric treatment of obesity. However, it remains controversial whether the decrease is due to change in body composition, or if it represents a downregulation in cellular metabolism. To examine this relationship, we reviewed studies of BMR in children, adolescents, adults, semistarved non-obese, anorexics, and weight-reducing obese. The relationship between BMR and fat-free mass (FFM) of children, lean adolescents, and lean and obese adults consuming sufficient energy could be described by a single line, BMR (MJ/d) = 2.44 + 0.084 FFM (SEE = 0.63, R2 = .80). Obese adolescents demonstrated BMRs greater than predicted and semistarved lean individuals demonstrated BMRs less than predicted by this relationship. Obese individuals demonstrated a reduced BMR during underfeeding, but less so than semistarved lean individuals. The reduction in BMR relative to FFM in semistarved lean individuals could not be explained by disproportionate reductions in body cell mass (BCM).

The relevance of metabolic rate in behavioral medicine research

This article reviews research relating metabolism to areas of interest to behavioral medicine. Metabolic rate has been investigated as a possible mediator of a variety of problems related to energy balance. Metabolic rate has also been utilized to investigate excessive cardiac activity that may be associated with cardiovascular disease. Although resting metabolic rate does not appear to be different in obese compared with nonobese, diet-induced thermogenesis is diminished in obese subjects. Caloric restriction produces a decline in metabolic rate in both obese and nonobese and further reduces the diet-induced thermogenic effect in obese. Exercise may prevent the decline in metabolic rate following caloric restriction. Anorexic individuals have a lowered metabolic rate that appears to increase rapidly after refeeding. Although bulimic individuals who purge via self-induced vomiting do not have a lower metabolic rate than matched control subjects, the frequency of purging has been found to be inversely related to resting metabolic rate. Metabolic rate has also been investigated as a possible mediator of weight regulation in individuals who smoke cigarettes and has been shown to decrease with smoking cessation. Tissue overperfusion, or an increase in cardiovascular activity above metabolic need, has been shown to increase peripheral resistance and may lead to hypertension.

Anorexia nervosa and the regulation of intake: a review

Recent work on the central mechanisms of food intake is reviewed in relation to anorexia nervosa. On the basis of the present review a number of conclusions are drawn as possible avenues for future research. A proposal is outlined for the investigation of L-dopa as a potential treatment for anorexia nervosa.