Different thermic effects of leptin in adolescent females with varying body fat content.

BACKGROUND & AIMS: Investigating the effect of leptin on energy expenditure in undernutrition might lead to a better understanding of the role of leptin in regulating body weight in humans. METHODS: 73 underweight female adolescents with anorexia nervosa (AN) were compared with 23 healthy normal weight (nwC), and 9 overweight girls (OW); 37 AN were followed during 7 months of weight recovery. Resting energy expenditure (REE, by indirect calorimetry), body composition (fat mass, FM; lean tissue mass, LTM; by Dual-Energy X-Ray Absorptiometry) and plasma hormones of leptin and 3,5,3'-Triiodothyronine (T(3)) were measured. RESULTS: In underweight, leptin, T(3) and REE adjusted for lean tissue mass (REE(LTM)) were decreased; in OW, FM and leptin were increased at unchanged T(3) and REE(LTM). There was a significant positive relation between FM and leptin at low and normal (AN, r(2) = 0.26; nwC, r(2) = 0.51, p < 0.001), but not at high adiposity. Leptin and REE(LTM) were positively associated in underweight (r(2) = 0.14, p = 0.001) but not in normal or overweight subjects. T(3) was linearly related to REE(LTM) over the whole range of adiposity (r(2) = 0.42, p < 0.001). With weight gain in AN (5.0 ± 3.5 kg) the relationship between leptin and REE(LTM) changed toward the conditions seen in normal weight controls. CONCLUSIONS: At low adiposity the interrelated fall of leptin and REE reflect an adaptive mechanism to preserve body weight. High leptin production associated with excessive adiposity was without effect on metabolic adaptation.

Body composition changes in female adolescents with anorexia nervosa.

BACKGROUND: Body weight provides limited information about nutritional status of patients with anorexia nervosa (AN). OBJECTIVES: Our objectives were to determine body composition (BC) changes, to find clinical predictors and endocrine correlates of total body protein (TBPr) depletion, and to compare results on fat mass (FM) obtained with anthropometry (skinfold measurements) and dual-energy X-ray absorptiometry (DXA) in patients with AN. DESIGN: Body weight, body mass index (BMI; in kg/m(2)), BC (with DXA and skinfold measurements), and TBPr [with in vivo neutron activation analysis (IVNAA)] was assessed in 50 AN patients (15.2 y) and 40 healthy sex- and age-matched controls. In 47 AN patients and 22 controls, hormone concentrations were measured. RESULTS: In AN patients, body weight (44.4 +/- 5.5 kg), BMI (16.7 +/- 1.6), and FM(DXA) (7.0 +/- 3.4 kg) were lower than in controls. Lean tissue mass by DXA (LTM(DXA)) was similar in AN patients and controls (35.7 +/- 4.3 compared with 35.8 +/- 4.5 kg), but TBPr was 87% of that of controls (8.1 +/- 1.0 compared with 9.2 +/- 1.2 kg; P < 0.001). Cortisol was high, testosterone was unchanged, and estradiol and insulin-like growth factor I were low. Severe protein depletion measured by IVNAA seen in 17 AN patients could not be identified with simpler methods. All except 1 of 26 AN patients with a BMI > 16.5 had normal TBPr. The difference in individual percentage of body fat measured with DXA and skinfold measurements came up to 9%. CONCLUSION: The severe protein depletion in 34% of AN patients was not accurately identified by LTM(DXA) or simpler methods, but a BMI > 16.5 indicated normal TBPr. Future studies need to compare DXA and skinfold measurements with a reference technique to assess FM in AN patients.

Association between intestinal tight junction permeability and whole-body electrical resistance in healthy individuals: a hypothesis.

OBJECTIVE: Intestinal permeability describes non-carrier-mediated modes of transport through the intestinal epithelium. Wrist-ankle bioimpedance analysis (BIA) is a standard method to determine body composition based on the measurements of whole-body electrical resistance and reactance values. The present report deals with the coincidentally observed associations between permeability results and electrical raw values of BIA and their subsequent reproduction in a larger group of individuals. METHODS: Tetrapolar wrist-ankle BIA was performed on day 1 in the initial sample (12 women, 36 +/- 11 y of age) and the validation sample (36 healthy subjects, 26 women and 10 men, 35 +/- 14 y of age). Intestinal permeability tests (lactulose and mannitol) were implemented within 1 wk thereafter. Wrist-ankle electrical resistance plus electrical resistance between current-conducting electrodes and voltage-sensing electrodes (Rtotal) was measured at 5 kHz and 100 kHz. RESULTS: Permeability and bioimpedance raw values were normal, indicating normal tight junction permeability and normal hydration. Lactulose correlated to R(50total) in the initial sample (rho = 0.639, P = 0.025) and in the validation sample (rho = 0.673, P < 0.001). Weaker associations to R(50total) were observed with mannitol (rho = 0.381, P = 0.008) and lactulose/mannitol (rho = 0.369, P = 0.010) in the total group of individuals. Regression analyses demonstrated that R(50total) alone accounted for 41.3% of the variance in lactulose permeability. CONCLUSION: The nature of the observed positive association between intestinal tight junction permeability and whole-body electrical resistance is unclear. We hypothesize that regulation involving submolecular mechanisms based on the principles of quantum physics might have caused the observed association. Such coherent mechanisms might possibly play a role in basal physiologic regulation in humans.

Total body protein in healthy adolescent girls: validation of estimates derived from simpler measures with neutron activation analysis.

BACKGROUND: Little recent and accurate information about body protein content in healthy adolescent girls is available. OBJECTIVE: The objective was to assess the total body nitrogen (TBN) and total body protein (TBPr) contents of fat-free mass (P:FFM) in a group of healthy adolescent girls and to validate previously published TBN prediction equations. DESIGN: TBN was measured with in vivo neutron activation analysis (TBNNAA). Bone mineral density and FFM were measured with dual-energy X-ray absorptiometry (FFMDXA), total body water and FFM were measured with bioimpedance analysis, and FFM was assessed by measuring skinfold thicknesses in 51 girls with a mean (+/- SD) age of 14.7 +/- 0.7 y. The validity of the TBN prediction equations was assessed with Bland-Altman analysis. RESULTS: TBNNAA in our adolescent group was higher (1.49 kg) than values reported in earlier studies of women (1.25 and 1.31 kg), and P:FFM was slightly higher (23%) than that documented in adults (19-21%). Previously published TBN equations showed either systematic bias or wide limits of agreement. CONCLUSION: A predictive equation derived from the present study population based on FFMDXA improves the prediction of TBN for groups of young girls but may not be helpful for individuals in clinical settings.