Gymnastik- och idrottshögskolan, GIH

BACKGROUND: Most studies indicate an inverse relationship between physical activity (PA) and body mass index (BMI). However, the impact of obesity on this relationship is unclear.

OBJECTIVE: To scrutinize the BMI/PA relationship by analysing multiple categories of PA from a sample with a wide BMI range.

DESIGN: PA was measured with accelerometry for 7 consecutive days during free-living conditions in 85 severely obese outpatients (mean BMI 42.7 kg/m(2) (s.d. 6.1); age 43.0 year (12.6)) and 193 control subjects (24.0 kg/m(2) (3.5); 41.6 year (13.0)). Six categories of PA were calculated from the accelerometer data (min/day of sedentary time, min/day of light PA, min/day of moderate PA, min/day of vigorous PA, activity counts/day and steps/day). Participants were stratified in obese and non-obese subgroups (BMI=30 kg/m(2) as cutoff). Associations between BMI and PA were examined in the total sample, and in subgroups. The impact of sex and age on the BMI/PA association was tested.

RESULTS: In the total sample, the association between BMI and PA was significant in all PA categories except for time spent sedentary (P=0.68). However, in subgroup analyses, the association between BMI and PA in non-obese was only significant for activity counts/day (r=-0.16, P<0.05) and vigorous intensity PA (r=-0.15, P=0.05). After adjustment for age, vigorous PA remained significantly associated with BMI in the non-obese (r=-0.17, P<0.05). In obese individuals, significant associations between BMI and PA were found for all six PA categories (age adjusted), sedentary time (r=0.26, P=0.05), light PA (r=-0.30, P<0.01), moderate PA (r=-0.35, P<0.01), vigorous PA (r=-0.39, P<0.001), activity counts/day (r=-0.50, P<0.001) and steps/day (r=-0.54, P<0.001).

CONCLUSION: The association between PA and BMI was weak in non-obese individuals. In contrast, BMI was highly significantly associated with PA in obese individuals. Longitudinal studies are needed to tease out the direction of association between PA and BMI across BMI categories, as the cross-sectional associations seem to be dependent on obesity status.

BACKGROUND: Abdominally obese women can reduce their health risk through regular physical activity. There is, however, little evidence on the effectiveness of interventions that promote physical activity long-term, such as cycling and walking to and from work.

METHODS: This intervention focused on physically active commuting (cycling and walking) in middle-aged (30-60 years), abdominally obese (waist circumference > or = 88 cm) women (n=120), recruited by newspaper advertisement. The intervention group was a moderate-intensity programme with physician meetings, physical activity prescriptions, group counselling and bicycles. The control group was a low-intensity group support programme with pedometers. We used a randomized, controlled, 2-armed design with 18 months duration and intention-to-treat analysis (data collection 2005-2006). Treatment success was defined as bicycling > or = 2 km/d (primary) or walking 10,000 steps per day (secondary).

RESULTS: At baseline, mean (s.d.) age was 48.2 years (7.4), waist circumference 103.8 cm (7.8), walking 8471 steps per day (2646), bicycling 0 km per day. Attrition at 18 months was 10% for the intervention group and 25% in the control group (P=0.03). The intervention group was more likely to achieve treatment success for cycling than controls: 38.7 vs 8.9% (odds ratio (OR)=7.8 (95% confidence interval=4.0 to 15.0, P<0.001)), but with no difference for compliance with the walking recommendation: 45.7 vs 39.3% (OR=1.2 (95% CI=0.7 to 2.0, P=0.50)). Commuting by car and public transport were reduced by 34% (P<0.01) and 37% (P<0.001), respectively, with no differences between groups. Both groups attained similar waist reductions (-2.1 and -2.6 cm, P=0.72).

CONCLUSIONS: Abdominally obese women can increase PA long-term through moderate-intensity behavioural support aimed at changing commuting habits.

BACKGROUND: Concern exists regarding gallstones as an adverse event of very-low-calorie diets (VLCDs; <800 kcal per day).

OBJECTIVE: To assess the risk of symptomatic gallstones requiring hospital care and/or cholecystectomy in a commercial weight loss program using VLCD or low-calorie diet (LCD).

DESIGN: A 1-year matched cohort study of consecutively enrolled adults in a commercial weight loss program conducted at 28 Swedish centers between 2006 and 2009. A 3-month weight loss phase of VLCD (500 kcal per day) or LCD (1200-1500 kcal per day) was followed by a 9-month weight maintenance phase. Matching (1:1) was performed by age, sex, body mass index, waist circumference and gallstone history (n=3320:3320). Gallstone and cholecystectomy data were retrieved from the Swedish National Patient Register.

RESULTS: One-year weight loss was greater in the VLCD than in the LCD group (-11.1 versus -8.1 kg; adjusted difference, -2.8 kg, 95% CI -3.1 to -2.4; P<0.001). During 6361 person-years, 48 and 14 gallstones requiring hospital care occurred in the VLCD and LCD groups, respectively, (152 versus 44/10 000 person-years; hazard ratio, 3.4, 95% CI 1.8-6.3; P<0.001; number-needed-to-harm, 92, 95% CI 63-168; P<0.001). Of the 62 gallstone events, 38 (61%) resulted in cholecystectomy (29 versus 9; hazard ratio, 3.2, 95% CI 1.5-6.8; P=0.003; number-needed-to-harm, 151, 95% CI 94-377; P<0.001). Adjusting for 3-month weight loss attenuated the hazard ratios, but the risk remained higher with VLCD than LCD for gallstones (2.5, 95% CI 1.3-5.1; P=0.009) and became borderline for cholecystectomy (2.2, 95% CI 0.9-5.2; P=0.08).

CONCLUSION: The risk of symptomatic gallstones requiring hospitalization or cholecystectomy, albeit low, was 3-fold greater with VLCD than LCD during the 1-year commercial weight loss program.