PEDIATRIC HIGHLIGHT
Changes in adipocyte hormones and lipid oxidation
associated with weight loss and regain in severely
obese adolescents
S Lazzer
1, M Vermorel
2, C Montaurier
1, M Meyer
3and Y Boirie
1*
1Protein-Energy Metabolism Research Unit, INRA, University of Auvergne, Clermont-Ferrand, France;
2Energy and Lipid
Metabolism Research Unit, INRA, Theix, St Gene`s Champanelle, France; and
3Hoˆtel-Dieu Pediatric Hospital, Human
Nutrition Research Centre in the Auvergne, Clermont-Ferrand, France
OBJECTIVE: To investigate changes in adipocyte hormones and lipid oxidation during and after a weight-reduction programme in severely obese adolescents.
DESIGN: Longitudinal-clinical investigation including a 9-month multidisciplinary weight-reduction programme in a specialised institution with lifestyle education, moderate energy restriction and regular physical activity, followed by a 4-month period at home.
SUBJECTS: A total of 26 (12 boys and 14 girls) severely obese adolescents (mean BMI: 33.9 kg/m2; 41.5% fat mass (FM)). MEASUREMENTS: Before starting (M0), at the end (M9), and 4 months after the end (M13) of the intervention blood samples were collected at fast, body composition was assessed by dual X-ray absorptiometry, and energy expenditure (EE) and substrate oxidation were assessed by whole-body indirect calorimetry over 24 h.
RESULTS: At M9, adolescents had lost 19.0% body weight (BW), 41.3% FM (Po0.001), with a minor fat free mass (FFM) loss in girls (6.4%, Po0.001) but no significant FFM changes in boys. Plasma leptin concentration at M9 was 70% lower (Po0.001), whereas plasma adiponectin concentration was 26.6% higher (Po0.001). The results also suggest that after adjustment for FFM and energy balance, sleeping and sedentary activity lipid oxidation rates were higher at M9 than at M0. At M13, plasma adiponectin, insulin, glucose and LDL concentrations returned to the initial levels, and leptin to an intermediate level in the 10 adolescents who had regained BW. Adjusted lipid oxidation rate decreased in both groups of subjects but it was not correlated to any change in plasma adipocyte hormones, which rather changed in relation to FM modifications.
CONCLUSION: Moderate energy restriction and regular moderate and high intensity physical activities in obese adolescents induced beneficial changes in BW and composition, lipid oxidation and blood parameters, especially adipocyte hormones. International Journal of Obesity (2005) 29, 1184–1191. doi:10.1038/sj.ijo.0802977
Keywords: substrate oxidation; whole-body calorimetry; adolescent; physical activity; leptin; adiponectin; hormones
Introduction
The prevalence of obesity and overweight has been increa-sing in children and adolescents throughout the world during the last decades.1,2The association between obesity
and metabolic complications justifies the importance of developing efficient weight-reduction programmes specifi-cally designed for obese adolescents. Energy restriction, a common treatment of obesity, is usually effective in achiev-ing short-term body weight (BW) and fat mass (FM) loss but
it is associated with fat-free mass (FFM) reduction, which could explain the usual decrease in basal metabolic rate (BMR),3and a further BW regain.
Lipid oxidation, especially muscle oxidation capacity, is a main determinant for obesity prevention, so that not only maintaining FFM but also the ability of FFM to utilise fatty acids should be the crucial objective of weight reduction and maintenance programmes. In obese adolescents, a signifi-cant association between FM and fasting lipid oxidation rate has been shown during a weight stable period,4 implying that FM loss might be associated with a lower lipid oxidation. Interestingly, lipid oxidation was lower in adults after weight loss than in lean subjects.5However, reduction
in lipid oxidation may be offset by regular practice of physical activity.6,7 Significant decreases in BW and FM,
Received 11 June 2004; revised 26 February 2005; accepted 23 March 2005
*Correspondence: Dr Y Boirie, Human Nutrition Laboratory, 58, rue MontalembertFBP 321, 63009 Clermont-Ferrand Cedex 1, France. E-mail: Yves.Boirie@sancy.clermont.inra.fr
without significant reductions in FFM and BMR, have been reported in children when physical activity and behaviour modifications were associated with hypocaloric diet.8Thus,
regular physical activity in combination with energy restric-tion may provide a fruitful strategy to preserve FFM, maintain daily energy expenditure (EE) and lipid oxidation during a weight-reduction programme.
The role of recently discovered adipocyte hormones in the regulation of energy metabolism and substrate oxidation in children with morbid obesity is still unknown. Indeed, longitudinal evaluation of metabolic modification during BW loss and BW regain is of great interest since it may provide information on the adaptive mechanisms that occur in response to weight changes in obese adolescents.
The objectives of the present study were, therefore, to investigate whether a multidisciplinary weight-reduction programme, including moderate energy restriction, progres-sive physical training and regular physical activity, is adequate to maintain lipid oxidation rate and improve the adipocyte hormone status in the short and medium term in severely obese adolescents, in spite of FM loss.
Subjects and methods
Subjects
A total of 26 (12 boys and 14 girls) severely obese adolescents aged 12–16 y were recruited from the Paediatrics Department of Clermont-Ferrand University Hospital. All subjects had a full medical history and physical examination, with the routine haematology and biochemistry screens and urine analysis. BW was stable during the previous last 2 months. The BMIs for gender and chronological age were above the 99th percentile.9 None of the subjects had evidence of significant disease, non-insulin-dependent diabetes mellitus or other endocrine disease, and none were taking medica-tions regularly or use of any medication known to influence energy metabolism.
Study protocol
The study was approved by the University Ethical Commit-tee on Human Research for Medical Sciences (AU # 361). The purpose and objective of the study were explained to each subject and his/her parents, and written informed consent was obtained before beginning the study. The adolescents spent 10 months, 5 days per week, in a specialised nursing institution, and weekend and 4 holidays weeks at home. Subjects, followed a 9-month personalised weight-reduction programme consisting of lifestyle education, physical acti-vity, dietary and psychological follow-up. At the end of the weight-reduction programme, the adolescents returned home. After 4 months, they spent 1 week in the specialised institution. Full testing sessions were conducted just before the beginning (month 0, M0), at completion of the 9-month weight-reduction period (month 9, M9) and 4 months later (month 13, M13). The testing session included assessment of
anthropometric characteristics, body composition, EE by whole-body calorimetry and blood sampling. In addition, individual anthropometric indexes and physical capacities were evaluated monthly to adjust physical training and food allowances. The latter were specially adjusted during the last 2 months to stabilise BW.
Diet and nutritional education
During the 9-month weight reduction period, personalised diets were offered on the basis of the baseline BMR test and physical activity level for each adolescent. Energy supply was adjusted to be close to 1.3 times initial BMR, that is about 15–20% less than estimated daily EE. Diet composition was formulated according to the French recommended daily allowances.10 During the weight-reduction period,
adoles-cents had dietetics lessons including choice and cooking of foods, and they were instructed to maintain their food habits after the end the weight-reduction period.
Physical activity
During the 9-month weight-reduction period, the adoles-cents participated in an exercise-training programme includ-ing two 40 min endurance and strength traininclud-ing sessions (preceded and followed by 5–7 min stretching) per week under heart rate (HR) monitoring and medical supervision. Intensity of endurance exercises (cycle ergometer, treadmill walking, stepper, and stationary rowing) was set at an HR corresponding to 55–60% of the initialVO. 2max. Strength
training was performed on universal gym equipment. Physical training intensity was adjusted monthly according to the results of the physical capacity tests. In addition, subjects had 2 h of physical education lessons (PEL) at school, and 2 h of aerobic leisure activities at the institution per week. The adolescents and their parents were also advised to practice leisure physical activities during the weekend and holidays.
Measurements
Anthropometric characteristics and body composition. BW was measured to the nearest 0.1 kg using a calibrated manual weighing scale (Seca 709, Les Mureaux, France). Height was measured to the nearest 0.5 cm on a standardised wall-mounted height board. Total body composition was assessed by dual X-ray absorptiometry (DXA) using Hologic QDR-4500 equipment and version 9.10 of total body scans software (Hologic Inc., Bedford, MA, USA). FFM was defined as the sum of nonbone lean tissue and bone mineral content. Hydration of the FFM was assumed to be constant (73.2%). The ability to measure changes in body composition by DXA was recently showed by Tylavsky et al.11
EE and substrate oxidation. In all, 24 h EE and substrate oxidation rates were measured by indirect calorimetry using
two comfortable open-circuit whole-body calorimeters.12
Measurements were obtained three times: before the begin-ning (M0), at completion of the weight-reduction pro-gramme (M9), and 4 months later (M13). The adolescents spent 36 h in the whole-body calorimeters, one evening and one night for adaptation and 24 h for measurement. They followed the same standardised activity programme com-posed of five main periods: (1) sleeping (8.5 h), (2) sedentary activities (watching television, video games, listening to music, board games, school work, 10.5 h), (3) miscellaneous activities (washing and dressing, making the bed and tidying the room, 1 h), (4) meals (breakfast, lunch, snack and dinner, 2 h), and (5) six 20-min exercises of walking at six different speeds (2 h). Before the beginning of the weight-reduction programme, subjects walked at their own speed on the treadmill and the slope was altered to obtain different intensities of exercises.
Gas exchanges were computed from outlet air flow, differences in gas concentrations between air entering and leaving the calorimeter, atmospheric pressure, chamber air temperature and hygrometry, after correction for the drift and time of response of the gas analysers and the variations of the quantities of CO2and O2in the calorimeters. The gas
analysers were calibrated twice a day using the same gas mixture during the whole study. In addition, the validity of gas exchange measurements was checked gravimetrically. EE was calculated using the equation of Brouwer13from the minute-to-minute measurement of gas exchanges. HR was measured by telemetry (Life scope 6, Nikon Kohden, Tokyo, Japan) and recorded continuously during the stay in the calorimeters.
Urine was collected over 24 h (starting at 0700 h) for the determination of urinary nitrogen excretion. Protein, glu-cose and lipid oxidation were calculated from gas exchanges and urinary nitrogen excretion using Ferrannini’s equa-tions,14during 24 h, sleep (between midnight and 0600 h), sedentary activities (except meals) and physical activities (walking). Daily energy balance was calculated as the difference between daily energy intake (EI) and daily EE.
In free-living conditions physical activity and EE were assessed using an activity diary and the HR-recording method. HR was monitored during seven consecutive days at M0, M9, and M13, and EE was calculated using the relationships established between HR and EE for each individual during the stays in the calorimeters.12
Energy intake. At the institution and in the calorimeters, food was offered ad libitum before the beginning (M0) and 4 months after the end of the weight-reduction period (M13), but according to individual rations during the weight-reduction period at M9, to simulate the adolescent food habits. The quantities of each food offered and not eaten were determined during 1 week at the Institution and over 24 h in the calorimeters for each testing period using an accurate balance (0.1) g. The nutrients and EI were assessed
using GENI software version 4.0 (MICRO 6, Villers les Nancy, France) based on the nutritive value of foods.15
Blood sampling. Blood samples were collected in the Vacutainerss
tubes (Belliver Industrial Estate, Plymouth, UK) containing EDTA from an antecubital vein between 0800 and 1000 h. after a 12-h overnight fast. Samples were centrifuged (at 4000 g for 10 min at 41C) and plasma was transferred into plastic tubes and kept at 801C until further analysis.
Plasma glucose concentration was determined by the GOD-PAP enzymatic method (Boehringer Mannheim Diag-nostic, France), plasma insulin concentration with Medgenix-Ins-Easia immunoenzymetric assay (Biosource Europe SA, Nivelles, Belgium), plasma glycerol concentration using the glycerin glycerol enzymatic bioanalysis UV method (R-Biopharm GmbH, Darmstadt, Germany), total plasma cholesterol (TC) concentration by CHOD-PAP enzymatic method (Boehringer Mannheim Diagnostic, France), plasma triacylglycerol (TAG) concentration by the GPO-PAP enzy-matic method (Boehringer Mannheim Diagnostic, France). High-density lipoprotein cholesterol (HDL) and low-density lipoprotein cholesterol (LDL) were determined using enzy-matic assays (Boehringer Mannheim Diagnostic, France) and plasma nonesterified fatty acids (NEFA) with NEFA C (Wako Chemicals GmbH, Neuss, Germany). Plasma leptin concen-trations were determined with a highly sensitive commercial human leptin solid phase sandwich ELISA (Biosource Inter-national, Inc., CA, USA), plasma adiponectin concentrations with a human adiponectin RIA kit radio-immunoassay (Linco Research, Inc., St.Charles, MO, USA), plasma thyroid hormones (3,5,30-triiodothyronine (T3) and thyroxine (T4))
concentrations using clinical assays kits (Abbott Division Diagnostic, Axsym System, Rungis, France).
Statistical analysis
Statistical analyses were performed using PROC REG of SAS software (version 6.12, 1996). The data are presented as LSMeans and s.e. Significance was set at Po0.05. The effects of sex or group (subjects who maintained BW vs subjects who regained BW), period (before, during and after the weight-reduction programme) and interaction (sex or group period) on physical characteristics, body composition, and biological parameters were tested using PROC MIXED of SAS software (version 6.12, 1996). The effects of sex and period (M0 vs M9 and M9 vs M13) on lipid oxidation rates during the main activities were tested by ANCOVA with FFM and energy balance as covariates, using PROC MIXED of SAS software (version 6.12, 1996). Stepwise multiple regressions were used to determine the significant predictors of BW and FM changes between M9 and M13.
Results
Short-term effects of the weight-reduction programme (M0–M9)
Physical characteristics of subjects. At M0 all subjects were severely obese since the BMI averaged 33. 9 (s.e. ¼ 0.6) kg/m29and the percentage of FM 41.5 (s.e. ¼ 1.8)%. Age and pubertal stage16 were significantly higher in girls than in boys (Po0.001) (Table 1). During the 9-month weight-reduction period, the pubertal stage increased significantly in boys (2.5 vs 3.5, s.e. ¼ 0.6, Po0.001) but not in girls. At M9, mean weight loss was 18.4 and 16.2 (s.e. ¼ 1.3) kg, height gain was 4.5 and 1.4 (s.e. ¼ 0.2) cm (Po0.001), and BMI decreased by 8.1 and 6.3 (s.e. ¼ 0.4) kg/m2in boys and girls, respectively (Po0.001). Weight loss was composed of 98% FM and 2% FFM in boys, but 79% FM and 21% FFM in girls.
EI and EE. During the food control weeks at M0 and M9, significant changes were shown in EI (11.23 vs 9.63, s.e. ¼ 0.53 MJ/day, Po0.001), and percentages of energy from carbohydrates (46 vs 50, s.e. ¼ 0.9%, Po0.001), from fat (38 vs 32, s.e. ¼ 1.0%, Po0.001) and from protein (16 vs 18, s.e. ¼ 0.5%, Po0.001).
For the same activity programme in the whole-body calorimeters, daily EE was 14.16 and 11.57 (s.e. ¼ 0.46) MJ/day (Po0.001) at M0 and M9, respectively.16
Con-sequently, energy balance was significantly lower at M9 than at M0 (0.2270.51 vs 3.2171.46 MJ/day, Po0.001). Similarly, in free-living conditions the main components of daily EE (sleeping, sedentary, and walking EE) decreased significantly between the M0 and M9 control periods (16.4, 18.9 and 30.1%, respectively, Po0.00117).
Substrate oxidation. After adjustment for FFM and energy balance, sex was not a significant determinant of lipid oxidation rates (0.67oPo0.85), and there were no signifi-cant interactions between sex and period (0.55oPo0.93)
during the stay in the whole-body calorimeters. Adjusted lipid oxidation rates were significantly higher at M9 than at M0, by 31.8 and 26.5% during sleep and sedentary activities (Po0.03 and Po0.05), respectively, and tended to be higher during the whole day (Po0.11). However, adjusted lipid oxidation rate during walking was not significantly different (Table 1).
Blood parameters. Fasting plasma glucose, insulin, trigly-cerides, total cholesterol, and LDL cholesterol concentra-tions, and LDL-to-HDL ratio decreased significantly during the weight-reduction period (Po0.001), whereas plasma HDL cholesterol concentration did not vary significantly (Table 2). Plasma NEFA concentration did not vary signifi-cantly, but plasma glycerol concentration decreased one-third (Po0.01). Plasma leptin concentration decreased by 71% on average (Po0.001), and its decrease was positively correlated to the decreases in total and LDL cholesterol (R ¼ 0.52) and triglycerides (R ¼ 0.39), but not with the decrease in FM (R ¼ 0.07). On the contrary, plasma adipo-nectin concentration increased by 42% in boys and 11% in girls (P ¼ 0.004). The increase in plasma adiponectin con-centration was negatively correlated with total FM (r ¼ 0.58, Po0.05) and trunk FM (r ¼ 0.61, Po0.05). Finally, plasma T3 concentration did not vary significantly, whereas plasma T4 increased slightly but significantly (Po0.05).
Changes after the end of the weight-reduction programme (M9–M13)
Physical characteristics of subjects. Two subjects (one boy and one girl) did not participate in the third testing session. During the 4-month period following the weight-reduction programme, BW, BMI, FFM and FM did not vary significantly in 14 subjects (seven boys and seven girls), but increased significantly (Po0.001) in 10 subjects (five boys and five
Table 1 Physical characteristics and lipid oxidation (LO) in adolescents before (M0) and at the end (M9) of the weight-reduction programme
Boys Girls Significance
M0 M9 M0 M9 s.e. P S P S Age (y) 13.5 14.2 14.7 15.5 0.69 0.001 0.037 0.997 Pubertal stage 2.5 3.5 4.1 4.4 0.61 0.001 0.038 0.002 Weight (kg) 89.8 71.4 92.8 76.6 7.18 0.001 0.401 0.357 Height (m) 1.64 1.68 1.65 1.66 0.05 0.001 0.666 0.001 BMI (kg/m2) 33.1 25.0 34.0 27.5 1.59 0.001 0.106 0.058 Fat-free mass (kg) 54.2 53.8 52.9 49.5 5.52 0.001 0.483 0.001 Fat mass (kg) 35.6 17.6 39.1 26.6 2.73 0.001 0.003 0.013 Daily LO (mg/min)a 61.2 71.9 64.5 74.2 6.3 0.114 0.679 0.936 Sleeping LO (mg/min)a 32.7 44.9 35.1 44.5 4.7 0.031 0.849 0.744
Sedentary act. LO (mg/min)a 61.6 82.7 63.8 75.8 8.0 0.058 0.781 0.551
Walking LO (mg/min)a 158.4 140.2 131.7 139.6 10.9 0.218 0.669 0.184
LSmeans and s.e. of LSmeans. Significance by ANOVA of the main effects of period (P) and sex (S); period sex interaction (P S).aLO: lipid oxidation rate adjusted for fat-free mass and energy balance.
girls; Table 3). Their percentage of FM increased from 28.4 to 31.1% (P ¼ 0.006), and their BW gain was composed of 59% FM and 41% FFM, on average.
EI and EE. During the control weeks at the institution, energy and fat intakes were not signicantly different between M9 and M13 in the 14 subjects who maintained their BW, whereas they were 1.20 MJ/day ( þ 13.0%, Po0.005) and 28.6 g/day ( þ 33.6%, Po0.07) higher, respectively, in M13 than in M9 in the 10 subjects who gained BW, FM and FFM.
In the whole-body calorimeters, for the same activity programme, DEE and energy costs (kJ/min) of sleeping, sedentary activities and walking did not change significantly between M9 and M13 in subjects who maintained their BW. On the contrary, DEE, energy costs of sleeping and walking were significantly higher in subjects who gained BW and FFM ( þ 0.61 MJ/day, þ 0.37 and þ 2.61 kJ/min, respectively,
Po0.01). However, after adjustment for FFM or BW the differences were not significant (data not shown).
Substrate oxidation. After adjustment for FFM and energy balance, group (subjects maintaining BW or subjects gaining BW) was not a significant determinant of lipid oxidation rates (0.49oPo0.94), and there were no significant interac-tions between group and period (0.16oPo0.69) during the stay in the whole-body calorimeters. Adjusted lipid oxida-tion rates were significantly lower at M13 than at M9, by 20.6, 56.6, 42.0, and 40.4% during sleep, sedentary activities, walking, and over the whole day, respectively (Table 3). Blood parameters. Glucose, insulinaemia, HDL cholesterol and T3 concentration increased significantly in both groups of subjects between M9 and M13 (Po0.02), whereas plasma NEFA and glycerol concentrations did not change signifi-cantly (Table 4). Plasma triglycerides, total cholesterol and
Table 2 Biological characteristics of adolescents before (M0) and at the end (M9) of the weight-reduction programme
Boys Girls Significance
M0 M9 M0 M9 s.e. P S P S Glucose (g/l) 0.73 0.65 0.76 0.68 0.038 0.009 0.397 0.936 NEFA (mmol/l) 0.60 0.53 0.60 0.52 0.044 0.151 0.820 0.942 Glycerol (mmol/l) 93.8 70.3 99.7 60.3 9.350 0.009 0.889 0.488 Cholesterol (g/l) 1.76 1.44 1.58 1.48 0.086 0.001 0.418 0.007 Triglycerides (g/l) 1.06 0.59 0.84 0.67 0.097 0.001 0.500 0.017 HDL cholesterol (g/l) 0.44 0.42 0.44 0.46 0.039 0.857 0.514 0.207 LDL cholesterol (g/l) 1.16 0.93 1.00 0.92 0.087 0.001 0.291 0.021 LDL-to-HDL ratio 2.72 2.25 2.33 2.11 0.315 0.001 0.370 0.356 Leptin (ng/ml) 40.8 7.3 52.3 21.0 4.734 0.001 0.006 0.529 Adiponectin (mg/ml) 14.6 20.8 12.9 14.3 4.067 0.004 0.260 0.053 Insulin (mIU/ml) 19.9 7.6 18.9 12.5 2.989 0.001 0.523 0.127 Triiodothyronin (ng/l) 2.89 2.89 2.57 2.29 0.082 0.114 0.001 0.099 Thyroxin (ng/l) 10.8 11.4 10.7 11.1 0.234 0.023 0.541 0.767
LSmeans and s.e. of LSmeans. Significance by ANOVA of the main effects of period (P) and sex (S); period sex interaction (P S).
Table 3 Changes in physical characteristics, body composition, energy expenditure (EE) and lipid oxidation (LO) in adolescents who maintained body weight (BWM) or regained body weight (BWR) between the end (M9) and 4 months after the end (M13) of the weight-reduction programme
BWM BWR Significance M9 M13 M9 M13 s.e. P G P G Age (y) 15.4 15.8 14.3 14.7 0.01 0.001 0.080 0.991 Pubertal stage 4.3 4.3 3.5 3.5 0.12 0.875 0.180 0.863 Weight (kg) 74.4 74.7 72.9 80.7 1.11 0.001 0.713 0.001 Height (m) 1.66 1.67 1.68 1.69 0.28 0.001 0.658 0.446 BMI (kg/m2) 26.8 26.8 25.7 28.1 0.34 0.001 0.961 0.001 Fat-free mass (kg) 51.3 51.4 52.2 55.4 0.42 0.001 0.609 0.001 Fat mass (kg) 23.1 23.3 20.7 25.3 0.90 0.001 0.931 0.001 Daily LO (mg/min)a 77.9 51.4 83.5 44.8 5.9 0.001 0.937 0.335 Sleep LO (mg/min)a 47.2 39.1 49.7 37.7 4.7 0.049 0.909 0.694
Sedentary act. LO (mg/min)a 83.0 41.4 92.7 34.8 7.2 0.001 0.838 0.274
Walking LO (mg/min)a 143.4 98.6 152.7 73.1 11.5 0.001 0.492 0.160
LSmeans and s.e. of LSmeans. Significance by ANOVA of the main effects of period (P) and group (G); period group interaction (P G).aLO: Lipid oxidation rate adjusted for fat-free mass and energy balance.
LDL cholesterol did not change significantly in subjects who maintained their BW, whereas they increased significantly in subjects who gained BW and FM. Changes in total choles-terol and LDL cholescholes-terol between M9 and M13 were correlated to changes in BMI (R ¼ 0.61 and 0.60, respectively, Po0.05) and FM (R ¼ 0.55 and 0.57, respectively, Po0.05). In addition, plasma leptin and adiponectin concentrations did not change significantly in subjects who maintained BW, whereas plasma leptin concentration increased significantly and adiponectin concentration decreased significantly in subjects who increased BW and FM (Table 4). Changes in leptin concentration were correlated to changes in BMI and FM (R ¼ 0.69 and 0.68, respectively, Po0.05).
Determinants of BW regain. Stepwise multiple regressions were computed between BW and FM changes between M9 and M13 (dependent variables), and plasma insulin, leptin, adiponectin, thyroid hormone concentrations, sleeping EE, lipid oxidation (mg/min/kg FFM), adiponectin/FM, leptin/ FM and adiponectin/insulin at M0 and M9 (independent variables). None of these variables were significant predictors of BW and FM changes between M9 and M13.
Discussion
The results of the present study show that (1) a 9-month multidisciplinary weight-reduction programme including physical training and regular physical activity, and a moderate energy restriction induced, in severely obese adolescents, significant increases in plasma adiponectin concentration and adjusted lipid oxidation rate during sleeping and sedentary activities, in spite of great BW and FM losses and decreases in EE and(2) 4 months after the end of the weight-reduction period, lipid oxidation dropped, and glucose concentration increased to the initial levels in all subjects; most other blood parameters did not change
significantly in subjects who maintained their BW, whereas they returned to the original values in subjects who gained BW and FM.
However, some reservation must be expressed about the effects of the weight-reduction programme on lipid oxida-tion rate between M0 and M9. Indeed, food was offered ad lib during the first 3 weeks at the institution and during the stay in the calorimeters at M0 to simulate usual food habits. However, food intake of subjects may have been reduced by changes in environment, food habits and food control (weighed diet record method) during the control week. Therefore, many subjects took advantage of being isolated in the calorimeters to eat more than at the institution. Lipid oxidation rates at M0 may have been partly inhibited by the increases in EI and energy balance during measurements in the calorimeter. On the contrary, subjects were offered the same individual rations both at the institution and in the calorimeter at M9. In addition, food allowances were specially adjusted during the last 2 months to stabilise BW. Energy balance was slightly negative (0.22 MJ/day) during measurement in the calorimeter at M9. The effect of differences in energy balance between M0 and M9 on lipid oxidation rate may have not been totally compensated for by adjustment for energy balance and FFM.
On the contrary, energy balances were similar at M9 and M13 (0.22 and þ 0.06 MJ/day, respectively) during mea-surements in the calorimeter. Consequently, after adjust-ment for FFM and energy balance, the lipid oxidation rates could be compared without risk of bias.
Lipid oxidation rate and physical activity
Lipid oxidation rate is affected by many other factors, especially FFM and physical activity. The increases in adjusted lipid oxidation rates during 24 h, sleeping and sedentary activities during the weight-reduction period (M0–M9) in spite of decreases in EE may result mainly from
Table 4 Changes in plasma metabolite and hormone concentrations in adolescents who maintained body weight (BWM) or regained body weight (BWR) between the end (M9) and 4 months after the end (M13) of the weight-reduction programme
BWM BWR Significance M9 M13 M9 M13 s.e. P G P G Glucose (g/l) 0.64 0.71 0.71 0.78 0.026 0.006 0.007 0.836 NEFA (mmol/l) 0.53 0.59 0.51 0.54 0.060 0.507 0.634 0.795 Glycerol (mmol/l) 57.8 64.5 73.5 67.5 9.898 0.964 0.531 0.434 Cholesterol (g/l) 1.47 1.52 1.45 1.67 0.045 0.002 0.339 0.047 Triglycerides (g/l) 0.63 0.65 0.61 0.76 0.058 0.069 0.344 0.142 HDL (g/l) 0.43 0.47 0.45 0.50 0.014 0.003 0.534 0.607 LDL (g/l) 0.94 0.95 0.90 1.05 0.038 0.030 0.621 0.063 Leptin (ng/ml) 15.2 14.1 16.1 28.0 3.164 0.014 0.138 0.004 Adiponectin (mg/ml) 17.5 18.1 17.4 14.2 0.997 0.181 0.654 0.040 Insulin (mIU/ml) 8.1 12.1 12.3 17.2 1.746 0.007 0.024 0.758 Triiodothyronin (ng/l) 2.5 2.7 2.7 3.1 0.095 0.017 0.144 0.234 Thyroxin (ng/l) 11.3 11.2 11.3 10.4 0.267 0.083 0.354 0.154
LSmeans and s.e. of LSmeans. Significance by ANOVA of the main effects of period (P) and group (G); period group interaction (P G).
physical training and regular moderate-intensity exercises17
in agreement with previous data in adults.18In fact, physical
activities may have counteracted the expected decline in fat oxidation observed when BW loss was obtained only with energy restriction in adults.19
The decrease in adjusted lipid oxidation rates observed in all subjects at M13 may result from the interruption of physical training after M9 and the increase in insulinaemia. In addition, no reliable information about physical activity of subjects could be collected between M9 and M13 because they were at home during the summer holidays, but none of them declared regular physical activities. Indeed, physical activity at 60–70% ofVO. 2max has a profound effect on fat
metabolism via lipolysis, uptake by tissues, especially muscle, through stimulation of the sympathetic nervous system19,20or maintenance of b-adrenergic receptors sensi-tivity,21and decrease in insulinaemia,22and on oxidation of
fatty acids19 through the b-oxidation and mitochondrial
activation.22 These results show the importance of
preser-ving lipid oxidation through sustained physical activity, after a weight-reduction period, because reduced lipid oxidation seems to be a determinant of BW regain also in adults.23
BW and biochemical and hormonal changes
Adiponectin is involved in the stimulation of fatty acid oxidation in muscle and liver, decrease in plasma trigly-cerides, and improvement of glucose metabolism through the increase in insulin sensitivity.24 In addition, adipose
tissue expression and plasma concentration of adiponectin are reduced in overweight and obese adults25and children,26 but energy metabolism was not simultaneously assessed in these studies. In the present study, the increase in plasma adiponectin concentration at M9 agrees with results of previous studies in adults after reduction of BW through lifestyle changes27or gastric partition surgery.28It was also associated with significant reductions in plasma glucose, insulin, triglycerides, total cholesterol, and LDL cholesterol concentrations, and LDL-to-HDL ratio in agreement with previous studies in obese adults.29These changes in meta-bolic and hormonal profiles indicate an obvious beneficial effect of moderate energy restriction, physical training and regular physical activity in adolescents with massive obesity. The decrease in plasma leptin concentration during the weight-reduction period agrees with the results of previous studies showing that plasma leptin concentration was lower in children30,31and in adults29after BW loss due to physical activity and/or energy restriction. However, decreases in plasma leptin concentrations may increase appetite and favour BW regain.32Since leptin has been reported to affect
EE, it is also possible that the plasma reductions of leptin may have an impact in the lower and adaptive response to reduction in EIs in these adolescents.
Physical activity reduces fasting insulin and increases insulin sensitivity33through enhancement of glucose
trans-port into muscle cells, and increased production of muscle glycogen34 independently of adipose tissue mass.35 These
findings agree with the results of the present study showing significant decreases in plasma insulin, glucose and leptin concentration during the weight-reduction period.
Conversely, 4 months after the end of the weight-reduction programme, plasma glucose, insulin, triglyceride, total cholesterol, LDL cholesterol, leptin and adiponectin concentrations were returned to the initial or to intermedi-ate values in the 10 adolescents who regained BW, FM and FFM. On the contrary, most of these blood parameters did not vary significantly between M9 and M13 in the 14 subjects who maintained BW, FFM and FM. However, adjusted lipid oxidation rates decreased significantly in both groups of subjects during the various activity periods probably because of the interruption of relatively intense physical activity during physical training, in agreement with the effects of detraining on lipid oxidation rate in previously trained sedentary adults.36
In conclusion, a weight-reduction programme including regular physical activity and a moderate energy restriction induced significant increases in plasma adiponectin concen-tration, together with decreases in plasma glucose, insulin, LDL cholesterol and leptin concentrations. The results also suggest an increase in lipid oxidation, in spite of great decreases in BW, FM and EE. At 4 months after leaving the institution, the 14 subjects who maintained BW and FM did not show significant changes in plasma metabolites and hormones concentrations (except glucose and insulin), whereas the 10 adolescents who had regained BW and FM had lost most of the beneficial effects of the weight-reduction programme. Nevertheless, lipid oxidation de-creased in both groups of subjects. These results demonstrate the importance of maintaining the same EI and moderate and high-intensity physical activities after the end of weight-reduction period to preserve the beneficial effects of the weight-reduction programme. The remaining issue would be to determine the necessary duration and intensity of physical activity in order to reach this goal.
Acknowledgements
We are grateful to the adolescents who participated in this study and their parents. We thank X Deries, MD, Director of the Children Medical Centre, M Taillardat, MD, in charge of adolescents, the teachers of adolescents and A Itier, dietician, for their contribution to set up the study. We are grateful to J Vernet for his advises for statistical analyses, L Morin, M Brandolini, C Giraudet, P Rousset and the staff of the Protein-Energy Metabolism Research Unit for their kind assistance during the study, and Dr R Taylor for revising the English. The study was supported by INRA (Institut National de la Recherche Agronomique) and the University of Auvergne. S Lazzer was granted by Danone Institute, Guigoz Laboratories, Roche Institute for Obesity and the Association
Franc-aise d’Etude et de Recherche sur l’Obe´site´ (AFERO). There are no real or potential conflicts of financial or personal interest with the financial sponsors of the scientific project.
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