ObjectivesTo determine the mean body mass index (BMI, kg/m2) and prevalence of low weight (BMI<20) and obesity (BMI≥30) in 3 population-based surveys, and to describe the longitudinal changes during 1994–2008 in mean BMI, and the prevalence of low weight and obesity.SettingA population study in Tromsø, Norway.ParticipantsA total of 29 688 different participants in 1 or more of 3 surveys (1994–1995, 2001–2002 and 2007–2008). Longitudinal analyses comprised 9845 participants aged 25–69 in 1994 who participated in the 1994–1995 and 2007–2008 surveys and 4202 men and women who participated in all 3 surveys.Outcome measuresMean age-specific and sex-specific BMI, prevalence of low weight and obesity, and changes in BMI and prevalence of low weight and obesity during 1994–2008, according to sex and birth cohort.ResultsThe age-adjusted (ages 30–84) prevalence of obesity increased from 9.8% and 11.8% in men and women, respectively, in 1994–1995 to 20.9% and 18.5%, respectively, in 2007–2008. The increase in mean age-adjusted BMI was stronger from 1994–1995 to 2001–2002 than from 2001–2002 to 2007–2008. Longitudinal results confirmed that the change in BMI from 1994–1995 to 2001–2002 was larger (0.9 kg/m2 (95% CI 0.8 to 1.0) in men and 1.3 kg/m2 (95% CI 1.2 to 1.4) in women) than from 2001–2002 to 2007–2008 (0.2 kg/m2 (95% CI 0.1 to 0.3) in men and women). The most recently born had the largest increase (p<0.001).ConclusionsThe mean BMI and the prevalence of obesity are still increasing in Tromsø, and the increase is strongest in the youngest age groups. However, the increase in BMI was less marked in the last period (from 2001–2002 to 2007–2008) than in the first period (1994–1995 to 2001–2002).

BackgroundAbdominal obesity increases all-cause mortality and is a risk factor for a number of diseases. There are few population-based studies of the longitudinal changes of abdominal obesity.MethodsBased on data from the Tromsø Study, we studied gender- and age-specific mean waist circumference and prevalence of abdominal overweight and abdominal obesity in two surveys in 1994–1995 (Tromsø 4, 6812 men and women aged 25 to 84) and 2007–2008 (Tromsø 6, 12,493 men and women aged 30 to 87). Furthermore, we describe the longitudinal changes of waist circumference and abdominal obesity during 13 years in 3144 subjects (aged 25–69 in 1994) who attended both surveys.ResultsCross-sectional analyses found a higher mean waist circumference in men than women and a direct relationship with age in both men and women in both Tromsø 4 and in Tromsø 6. As the WHO cut-off points for abdominal obesity are gender-specific, however, the prevalence of abdominal obesity was lower in men than in women. In 2007–2008, approximately 37 and 55 % of men and women, respectively, were classified as abdominally obese. Thirteen years before, in 1994–1995, the corresponding figures were 20 and 35 %. Longitudinal analyses of changes during the 13-year period clearly demonstrated that mean waist circumference increased in all examined birth cohorts in both men (mean change 6.1 cm) and women (mean change 8.4 cm), but increased more markedly the younger the subjects were. The prevalence of abdominal obesity in men aged 25–34 increased from 5 % in 1994 to 31 % 13 years later. The prevalence of abdominal obesity more than doubled among both men and women.ConclusionsThe increasing mean waist circumference is of concern. There is a need for further longitudinal studies of the changes in waist circumference.

BackgroundOverweight individuals desire a lower weight than they actually have. Little is known on the extent to which this discrepancy is reduced over time due to adaptation or resignation. The aim of this study is to describe cross-sectional relationships and longitudinal changes in desired body weight and differences between actual and desired body weight according to gender, age and category of body mass index in a large, adult cohort in Tromsø, Norway.MethodsCross-sectional analyses of 8960 men and 9992 women aged 25–69 participating in Tromsø 4 (during 1994–1995), and longitudinal analyses of 3210 men and 3689 women participating in both Tromsø 4 (during 1994–1995) and Tromsø 6 (during 2007–2008). Simple descriptive statistics and linear regression was used to describe actual and desired weight, the difference between them, and how gender and age are related to the changes in actual and desired weight over this 13-year period.ResultsThe difference between actual and desired body weight was largest for the obese and higher among the overweight than the normal weight for both genders. While normal weight men were quite satisfied with their body weight, normal weight women were not. Actual weight increased more than desired weight for all age groups and both genders except the oldest women. The difference between change in actual body weight and change in desired body weight during the 13-year follow-up was significantly larger among men (2.0 kg) than women (1.5 kg) (p < 0.001), and larger among young than older adults (p < 0.001). Adjusting for level of education had no impact on this relationship. Furthermore, the association between age and the difference between change in actual body weight during the 13 years and change in desired body weight in the same period did not differ between men and women and, in gender specific analyses, between subjects with normal weight and those who were overweight or obese at start of follow-up.ConclusionOlder people adapt more to weight gain than younger age groups, with clear gender differences. Further studies of longitudinal changes in desired weight are warranted.Electronic supplementary materialThe online version of this article (doi:10.1186/s40608-016-0120-6) contains supplementary material, which is available to authorized users.

BackgroundIt is not clear how physical activity affects body composition in adolescents. Physical activity levels are often reduced during this period, and the relative proportion of body fat mass and lean mass undergo natural changes in growing adolescents. We aimed to examine whether self-reported physical activity in leisure time at baseline or change in activity during follow-up affect changes in four measures of body composition; body mass index (kg/m2), waist circumference, fat mass index (fat mass in kg/m2) and lean mass index (lean mass in kg/m2).MethodsWe used data from the Tromsø Study Fit Futures, which invited all first year students in upper secondary high school in two municipalities in northern Norway in 2010–2011. They were reexamined in 2012–2013. Longitudinal data was available for 292 boys and 354 girls. We used multiple linear regression analyses to assess whether self-reported level of physical activity in leisure time at baseline predicted changes in body composition, and analysis of covariance to assess the effects of change in level of activity during follow-up on change in body composition. All analyses were performed sex-specific, and a p-value of < 0.05 was considered statistically significant.ResultsThere were no associations between self-reported leisure time physical activity in the first year of upper secondary high school and changes in any of the considered measure of body composition after 2 years of follow up, with the exception of waist circumference in boys (p = 0.05). In boys, change in fat mass index differed significantly between groups of activity change (p < 0.01), with boys adopting activity or remaining physically active having less increase in fat mass index than the consistently inactive. In girls, change in lean mass index differed significantly between groups of activity change (p = 0.04), with girls adopting physical activity having the highest increase.ConclusionsSelf-reported leisure time physical activity does not predict changes in body composition in adolescents after 2 years of follow up. Change in the level of physical activity is associated with change in fat mass index in boys and lean mass index in girls.

ObjectiveTo examine whether occupational physical activity changes predict future body mass index (BMI) changes.MethodsThis longitudinal cohort study included adult participants attending ≥3 consecutive Tromsø Study surveys (examinations 1, 2 and 3) from 1974 to 2016 (N=11 308). If a participant attended >3 surveys, the three most recent surveys were included. Occupational physical activity change (assessed by the Saltin-Grimby Physical Activity Level Scale) was computed from the first to the second examination, categorised into persistently inactive (n=3692), persistently active (n=5560), active to inactive (n=741) and inactive to active (n=1315). BMI change was calculated from the second to the third examination (height being fixed at the second examination) and regressed on preceding occupational physical activity changes using analysis of covariance adjusted for sex, birth year, smoking, education and BMI at examination 2.ResultsOverall, BMI increased by 0.84 kg/m2 (95% CI 0.82 to 0.89). Following adjustments as described previously, we observed no differences in BMI increase between the occupational physical activity change groups (Persistently Inactive: 0.81 kg/m2, 95% CI 0.75 to 0.87; Persistently Active: 0.87 kg/m2, 95% CI 0.82 to 0.92; Active to Inactive: 0.81 kg/m2, 95% CI 0.67 to 0.94; Inactive to Active: 0.91 kg/m2, 95% CI 0.81 to 1.01; p=0.25).ConclusionWe observed no prospective association between occupational physical activity changes and subsequent BMI changes. Our findings do not support the hypothesis that occupational physical activity declines contributed to population BMI gains over the past decades. Public health initiatives aimed at weight gain prevention may have greater success if focusing on other aspects than occupational physical activity.