objective: Physical activity (PA) begins to decline in adolescence with a concomitant increase in weight. We hypothesized that a vicious circle may arise between decreasing PA and weight gain from adolescence to early adulthood. Methods and Procedures: PA and self-perceived physical fitness assessed in adolescents (16-18 years of age) were used to predict the development of obesity (BMI ≥30 kg/m 2 ) and abdominal obesity (waist ≥88 cm in females and ≥102 cm in males) at age 25 in 4,240 twin individuals (90% of twins born in Finland, 1975Finland, -1979. Ten 25-year-old monozygotic (MZ) twin pairs who were discordant for obesity (with a 16 kg weight difference) were then carefully evaluated for current PA (using a triaxial accelerometer), total energy expenditure (TEE, assessed by means of the doubly labeled water (DLW) method), and basal metabolic rate (BMR, assessed by indirect calorimetry). Results: Physical inactivity in adolescence strongly predicted the risk for obesity (odds ratio (OR) 3.9, 95% confidence interval (CI) 1.4-10.9) and abdominal obesity (4.8, 1.9-12.0) at age 25, even after adjusting for baseline and current BMI. Poor physical fitness in adolescence also increased the risk for overall obesity (5.1, 2.0-12.7) and abdominal obesity (3.2, 1.5-6.7) in adulthood. Physical inactivity was both causative and secondary to the development of obesity discordance in the MZ pairs. TEE did not differ between the MZ co-twins. PA was lower whereas BMR was higher in the obese co-twins. Discussion: Physical inactivity in adolescence strongly and independently predicts total (and especially) abdominal obesity in young adulthood, favoring the development of a self-perpetuating vicious circle of obesity and physical inactivity. Physical activity should therefore be seriously recommended for obesity prevention in the young.

OBJECTIVE: To investigate whether walking or resistance training improves weight maintenance after weight loss when added to dietary counselling. DESIGN: Two months' weight reduction with very-low-energy-diet (VLED) followed by randomization into three groups (control, walking, resistance training) for 6 months' weight maintenance (WM) program and 23 months' unsupervised followup. During VLED and WM all groups received similar dietary counselling. SUBJECTS: The main inclusion criteria were BMI > 30 kg=m 2 , waist > 100 cm and physical inactivity (exercise once a week). Ninety healthy, obese (mean BMI 32.9 kg=m 2 and waist 112.5 cm), 35 -50 y-old men started the study and 68 were measured at the end of the study. MEASUREMENTS: Weight and body composition assessed by underwater weighing. Exercise diaries and dietary records to assess energy balance. RESULTS: During VLED the mean body weight decreased from 106.0 (s.d. 9.9) kg to 91.7 (9.4) kg. Weight was regained mostly during follow-up and in the end of the study the mean weight in groups was 99.9 -102.0 kg. Exercise training did not improve short or long-term weight maintenance when compared to the control group. However, resistance training attenuated the regain of body fat mass during WM (P ¼ 0.0l), but not during follow-up. In the combined groups the estimated total energy expenditure (EE) of reported physical activity was associated with less weight regain during WM. EE of 10.1 MJ=week was associated with maintaining weight after weight loss. EE of physical activity tended to decrease after WM in exercise groups due to poor long-term adherence to prescribed exercise. Energy intake seemed to increase during follow-up. CONCLUSION: Exercise training of moderate dose did not seem to improve long-term weight maintenance because of poor adherence to prescribed exercise.

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Objectives: To test and compare the validity of a body mass index (BMI)-based prediction equation and an impedance-based prediction equation for body fat percentage among various European population groups. Design: Cross-sectional observational study. Settings: The study was performed in five different European centres: Maastricht and Wageningen (The Netherlands), Milan and Rome (Italy) and Tampere (Finland), where body composition studies are routinely performed. Subjects: A total of 234 females and 182 males, aged 18 -70 y, BMI 17.0 -41.9 kg=m 2 . Methods: The reference method for body fat percentage (BF% REF ) was either dual-energy X-ray absorptiometry (DXA) or densitometry (underwater weighing). Body fat percentage (BF%) was also predicted from BMI, age and sex (BF% BMI ) or with a hand-held impedance analyser that uses in addition to arm impedance weight, height, age and sex as predictors (BF% IMP ). Results: The overall mean ( AE s.e.) bias (measured minus predicted) for BF% BMI was 0.2AE 0.3 (NS) and70.7 AE 0.3 (NS) in females and males, respectively. The bias of BF% IMP was 0.2 AE 0.2 (NS) and 1.0 AE 0.4 (P < 0.01) for females and males, respectively. There were significant differences in biases among the centres. The biases were correlated with level of BF% and with age. After correction for differences in age and BF% between the centres the bias of BF% BMI was not significantly different from zero in each centre and was not different among the centres anymore. The bias of BF% IMP decreased after correction and was significant from zero and significant from the other centres only in males from Tampere. Generally, individual biases can be high, leading to a considerably misclassification of obesity. The individual misclassification was generally higher with the BMIbased prediction. Conclusions: The prediction formulas give generally good estimates of BF% on a group level in the five population samples, except for the males from Tampere. More comparative studies should be conducted to get better insight in the generalisation of prediction methods and formulas. Individual results and classifications have to be interpreted with caution.

The favorable changes seen in ox-LDL particles and serum lipids during weight reduction could be maintained by keeping the weight reduced, which may indicate decreased risk of atherosclerosis. But weight regain causes a resurge of ox-LDL.