Prospective associations between sedentary lifestyle and BMI in midlife

Body weight change during a smoking cessation intervention for individuals with overweight or obesity

INTRODUCTION

A more comprehensive understanding of the factors regarding weight control in individuals with overweight or obesity after quitting smoking is needed. The study aimed to analyze the changes of in-treatment variables during a smoking cessation intervention and examine their impact on weight.

METHODS

A total of 120 individuals who smoke with overweight or obesity (MBMI = 31.75 ± 4.31; 54.16 % female) participated in a cognitive-behavioral therapy for smoking cessation and weight control or the same treatment plus contingency management. Weight, smoking variables (cotinine and continuous abstinence), eating behaviors (appetite, grazing), exercise, and sleep were assessed weekly throughout the treatment.

RESULTS

More participants gained weight over time with reduced nicotine use or abstinence. There was a tendency during treatment to increase appetite and exercise time, while grazing episodes and sleeping hours remained stable. Higher baseline weight (p < .001), greater cotinine reduction (p = .021) and time (p = .009) were associated with greater weight gain, while more hours of exercise (p = .003), no appetite changes (p = .003) and diminished appetite (p < .001) were associated with less gain over the treatment. Both treatment conditions showed similar results in all in-treatment variables.

DISCUSSION

Individuals with overweight and obesity with higher baseline weight and higher baseline cotinine levels during smoking cessation interventions may require special attention to improve weight outcomes. Exercise and appetite regulation may be useful for mitigating weight gain in smoking cessation interventions for individuals with overweight or obesity.

Device-worn measures of sedentary time and physical activity in South Asian adults at high risk for type 2 diabetes in Metro-Vancouver, Canada

Background

South Asians have high incidence of chronic disease. Physical activity (PA) and sedentary time are modifiable risk factors for chronic disease but their assessment in South Asians has been primarily based on self-report. This study presents directly-measured PA and sedentary time in South Asian adults in Canada.

Methods

A subset of 100 South Asian participants from a larger study who were identified at being at a higher risk for type 2 diabetes wore Actical accelerometers for 7 days. Anthropometric measures were taken and socio-demographic factors including age, income, education level, years since immigration, presence of children under the age of 12 years in the household and employment status were self-reported.

Results

Ninety-one participants (mean age 65.6 years) provided valid accelerometer data. Participants accumulated mean 673.5 (95% CI: 656.6, 691.0) min/day sedentary time, 130.5 (95% CI: 117.3, 145.3) min/day light PA (LPA) and 2.3 (95% CI: 1.3, 4.2) min/day moderate-to-vigorous PA (MVPA). For sedentary time and LPA, sex and BMI explained 51% of variability. For MVPA, BMI, season of assessment and employment status explained 23% variability with those who were employed accumulating significantly higher mean min/day of MVPA compared to those who were unemployed; (5.8, 95% CI: 1.5, 21.7) vs (1.5, 95% CI: 5.3, 20.0) respectively.

Conclusion

High sedentary time, and low MVPA indicates the need to focus health promotion efforts on shifting sedentary time into LPA while trying to increase MVPA. Future studies need to be based on larger, representative samples of South Asians.

Forecasting Obesity and Type 2 Diabetes Incidence and Burden: The ViLA-Obesity Simulation Model

Background

Obesity is a major public health problem affecting millions of Americans and is considered one of the most potent risk factors for type 2 diabetes. Assessing future disease burden is important for informing policy-decision making for population health and healthcare.

Objective

The aim of this study was to develop a computer model of a cohort of children born in Los Angeles County to study the life course incidence and trends of obesity and its effect on type 2 diabetes mellitus.

Methods

We built the Virtual Los Angeles cohort—ViLA, an agent-based model calibrated to the population of Los Angeles County. In particular, we developed the ViLA-Obesity model, a simulation suite within our ViLA platform that integrated trends in the causes and consequences of obesity, focusing on diabetes as a key obesity consequence during the life course. Each agent within the model exhibited obesity- and diabetes-related healthy and unhealthy behaviors such as sugar-sweetened beverage consumption, physical activity, fast-food consumption, fresh fruits, and vegetable consumption. In addition, agents could gain or lose weight and develop type 2 diabetes mellitus with a certain probability dependent on the agent's socio-demographics, past behaviors and past weight or type 2 diabetes status. We simulated 98,230 inhabitants from birth to age 65 years, living in 235 neighborhoods.

Results

The age-specific incidence of obesity generally increased from 10 to 30% across the life span with two notable peaks at age 6–12 and 30–39 years, while that of type 2 diabetes mellitus generally increased from <2% at age 18–24 to reach a peak of 25% at age 40–49. The 16-year risks of obesity were 32.1% (95% CI: 31.8%, 32.4%) for children aged 2–17 and 81% (95% CI: 80.8%, 81.3%) for adults aged 18–65. The 48-year risk of type 2 diabetes mellitus was 53.4% (95% CI: 53.1%, 53.7%) for adults aged 18–65.

Conclusion

This ViLA-Obesity model provides an insight into the future burden of obesity and type 2 diabetes mellitus in Los Angeles County, one of the most diverse places in the United States. It serves as a platform for conducting experiments for informing evidence-based policy-making.

Mendelian randomization suggests a bidirectional, causal relationship between physical inactivity and adiposity

Physical inactivity and increased sedentary time are associated with excess weight gain in observational studies. However, some longitudinal studies indicate reverse causality where weight gain leads to physical inactivity and increased sedentary time. As observational studies suffer from reverse causality, it is challenging to assess the true causal directions. Here, we assess the bidirectional causality between physical inactivity, sedentary time, and adiposity by bidirectional Mendelian randomization analysis. We used results from genome-wide association studies for accelerometer-based physical activity and sedentary time in 91,105 individuals and for body mass index (BMI) in 806,834 individuals. We implemented Mendelian randomization using CAUSE method that accounts for pleiotropy and sample overlap using full genome-wide data. We also applied inverse variance-weighted, MR-Egger, weighted median, and weighted mode methods using genome-wide significant variants only. We found evidence of bidirectional causality between sedentary time and BMI: longer sedentary time was causal for higher BMI [beta (95% CI) from CAUSE method: 0.11 (0.02, 0.2), p = 0.02], and higher BMI was causal for longer sedentary time (0.13 (0.08, 0.17), p = 6.3 x 10^-4). Our analyses suggest that higher moderate and vigorous physical activity are causal for lower BMI (moderate: –0.18 (-0.3,–0.05), p = 0.006; vigorous: –0.16 (-0.24,–0.08), p = 3.8 × 10^-4), but indicate that the association between higher BMI and lower levels of physical activity is due to horizontal pleiotropy. The bidirectional, causal relationship between sedentary time and BMI suggests that decreasing sedentary time is beneficial for weight management, but also that targeting adiposity may lead to additional health benefits by reducing sedentary time.

Physical Activity and Subsequent Change in Body Weight, Composition and Shape: Effect Modification by Familial Overweight

BACKGROUND

Physical activity (PA) has been shown to attenuate the genetic risk of obesity as measured using polygenic risk scores. However, familial obesity history might be an easier predictor. We examined associations between PA and subsequent changes in BMI, body fat percentage (BF%) and waist circumference (WC) among participants with and without adiposity and a familial overweight.

METHODS

In total, 1971 participants from the Danish MONICA cohort were included. Mean differences for 6-year changes in BMI, BF% and WC across PA levels were estimated. Association between walking and biking and subsequent change in adiposity were analysed. Effect modification by familial obesity was assessed by adding product terms to the models.

RESULTS

We observed weak associations between leisure PA level and changes in WC [participants with low PA: 3.4 cm (95%CI: 2.8;4.0), participants with high PA: 2.4 cm (95%CI: 1.8;3.0)], with no evidence of effect modification by familial obesity. We found effect modification in analyses on walking and biking in relation to changes in BMI (P-interaction<0.01) and BF% (P-interaction=0.04), suggesting lower gain with more hours of activity among participants with adiposity and familial overweight.

CONCLUSIONS

The results were modest but suggested that PA, especially walking and biking, may prevent future adiposity.

Changes in leisure time physical activity unrelated to subsequent body weight changes, but body weight changes predicted future activity

Physical activity and obesity are known to be associated. We investigated whether a change in leisure time physical activities (LTPA) predicts a subsequent weight change, or vice versa.We used data from a longitudinal study among Danish adults surveyed in 1983-1984, 1987-1988, and 1993-1994. Between two sequential surveys, the change in LTPA was grouped as no change, became less or more active; the change in body weight was defined as no change, lost or gained of more than one body mass index (BMI) unit.Among 2386 adults, change in LTPA was not associated with subsequent weight change. However, a loss in body weight (BMI change < -1 unit) was associated with subsequent either becoming less [OR = 1.49, 95% CI (1.03-2.15)] or borderline more active [OR = 1.37, 95% CI (0.99-1.90)]. Subgroup analyses showed particularity among females that a loss in body weight was associated with subsequent becoming more active [OR = 1.83, 95% CI (1.15-2.89)].Our results suggest that change in LTPA is unrelated to subsequent weight change, but loss in body weight seems related to subsequent more active among female adults.

The bidirectional associations between leisure time physical activity change and body mass index gain. The Tromsø Study 1974-2016

OBJECTIVES

To examine whether leisure time physical activity changes predict subsequent body mass index (BMI) changes, and conversely, whether BMI changes predict subsequent leisure time physical activity changes.

METHODS

This prospective cohort study included adults attending ≥3 consecutive Tromsø Study surveys (time: T1, T2, T3) during 1974-2016 (n = 10779). If participants attended >3 surveys, we used the three most recent surveys. We computed physical activity change (assessed by the Saltin-Grimby Physical Activity Level Scale) from T1 to T2, categorized as Persistently Inactive (n = 992), Persistently Active (n = 7314), Active to Inactive (n = 1167) and Inactive to Active (n = 1306). We computed BMI change from T2 to T3, which regressed on preceding physical activity changes using analyses of covariance. The reverse association (BMI change from T1 to T2 and physical activity change from T2 to T3; n = 4385) was assessed using multinomial regression.

RESULTS

Average BMI increase was 0.86 kg/m² (95% CI: 0.82-0.90) from T2 to T3. With adjustment for sex, birth year, education, smoking and BMI at T2, there was no association between physical activity change from T1 to T2 and BMI change from T2 to T3 (Persistently Inactive: 0.89 kg/m² (95% CI: 0.77-1.00), Persistently Active: 0.85 kg/m² (95% CI: 0.81-0.89), Active to Inactive: 0.90 kg/m² (95% CI: 0.79-1.00), Inactive to Active 0.85 kg/m² (95% CI: 0.75-0.95), p = 0.84). Conversely, increasing BMI was associated with Persistently Inactive (odds ratio (OR): 1.17, 95% CI: 1.08-1.27, p < 0.001) and changing from Active to Inactive (OR: 1.16, 95% CI: 1.07-1.25, p < 0.001) compared with being Persistently Active.

CONCLUSIONS

We found no association between leisure time physical activity changes and subsequent BMI changes, whereas BMI change predicted subsequent physical activity change. These findings indicate that BMI change predicts subsequent physical activity change at population level and not vice versa.

Evidence for shared genetics between physical activity, sedentary behaviour and adiposity-related traits

Observational, cross-sectional and longitudinal studies showed that physical activity and sedentary behaviour are associated with adiposity-related traits, apparently in a bidirectional manner. Physical activity is also suggested to suppress the genetic risk of adiposity. Since phenotypic associations with genetic variants are not subject to reverse causation or confounding, they may be used as tools to shed light on cause and effect in this complex interdependency. We review the evidence for shared genetics of physical activity and adiposity-related traits and for gene-by-physical activity interactions on adiposity-related traits in human studies. We outline limitations, challenges and opportunities in studying and understanding of these relationships. In summary, physical activity and sedentary behaviour are genetically correlated with body mass index and fat percentage but may not be correlated with lean body mass. Mendelian randomisation analyses show that physical activity and sedentary behaviour have bidirectional relationships with adiposity. Several studies suggest that physical activity suppresses genetic risk of adiposity. No studies have yet tested whether adiposity enhances genetic predisposition to sedentariness. The complexity of the comprehensive causal model makes the assessment of the single or combined components challenging. Substantial progress in this field may need long-term intervention studies.

Cumulative Exposure to Long Working Hours and Occurrence of Ischemic Heart Disease: Evidence From the CONSTANCES Cohort at Inception

Background

Long‐working hours (LWH) are a probable risk factor for ischemic heart diseases (IHD); however, no previous study has considered duration of exposure to LWH when addressing this topic. We aimed to determine the association between cumulative exposure to LWH and IHD while accounting for relevant confounders.

Methods and Results

In this retrospective study, we included all baseline participants from the French population‐based cohort CONSTANCES. Part‐time employees and those who reported a cardiac event in the 5 years before LWH exposure were excluded. From self‐administered questionnaires and clinical examinations, we obtained participants’ age, sex, body mass index, occupational status, smoking habits, high blood pressure, diabetes mellitus, familial history of cardiovascular disease, dyslipidemia, exposure to LWH, and its duration. We defined LWH as working for >10 hours daily for at least 50 days per year. The main outcome was reported history of IHD, ie, myocardial infarction or angina pectoris, during a clinical examination. Of 137 854 included participants, 69 774 were men. There were 1875 cases (1.36%) of IHD, and exposure to LWH was reported by 42 462 subjects (30.8%) among whom 14 474 (10.50%) reported exposure for at least 10 years. Overall, exposure to LWH for ≥10 years was associated with an increased risk of IHD, adjusted odds ratio (aOR) 1.24 (1.08–1.43), P=0.0021. In stratified analyses, this effect was not observed in women, but was significant amongst men, aOR 1.28 (1.11–1.48), P=0.0008.

Conclusions

This large population‐based study supports an association between cumulative exposure to LWH and IHD in men. Future research should consider relevant strategies for reducing LWH exposure and duration.

Bidirectional 10-year associations of accelerometer-measured sedentary behavior and activity categories with weight among middle-aged adults

BACKGROUND

Although higher sedentary behavior (SB) with low light intensity (LPA) and moderate-to-vigorous intensity physical activity (MVPA) are thought to increase risk for obesity, other data suggest excess weight may precede these behaviors in the causal pathway. We aimed to investigate 10-year bidirectional associations between SB and activity with weight.

METHODS

Analysis included 886 CARDIA participants (aged 38-50 years, 62% female, 38% black) with weight and accelerometry ( ≥ 4 days with ≥ 10 h/day) collected in 2005-6 (ActiGraph 7164) and 2015-6 (ActiGraph wGT3X-BT). Accelerometer data were calibrated, harmonized, and expressed as counts per minute (cpm) and time-dependent intensity categories (min/day of SB, LPA, and MVPA; SB and MVPA were also separated into long-bout and short-bout categories). Linear regression models were constructed to estimate adjusted associations of baseline activity with 10-year change in weight and vice versa. When activity categories were the independent variables, standardized regression coefficients (βstd.) estimated associations of replacing SB with a one SD increase in other categories, adjusted for accelerometer wear time.

RESULTS

Over 10-years, weight increased by a mean 2.55 ± 8.05 kg and mean total activity decreased by 50 ± 153 cpm. In adjusted models, one SD higher baseline mean total activity (βstd. = -1.4 kg, p < 0.001), LPA (βstd. = -0.80 kg, p = 0.013), total MVPA (βstd. = -1.07 kg, p = 0.001), and long-bout MVPA (βstd. = -1.20 kg, p < 0.001) were associated with attenuated 10-year weight gain. Conversely, a one SD higher baseline weight was associated with unfavorable 10-year changes in daily activity profile including increases in SB (βstd. = 12.0 min, p < 0.001) and decreases in mean total activity (βstd. = 14.9 cpm, p = 0.004), LPA (βstd. = 8.9, p = 0.002), and MVPA (βstd. = 3.5 min, p = 0.001). Associations varied by race and gender.

CONCLUSIONS

Higher SB with lower activity and body weight were bidirectionally related. Interventions that work simultaneously to replace SB with LPA and long-bout MVPA while also using other methods to address excess weight may be optimal.

Prolonged sedentary time adversely relates to physical activity and obesity among preoperative bariatric surgery patients

BACKGROUND

Bariatric surgery patients spend much of their waking time sedentary. Yet, little is known about their patterns of accumulation of sedentary time (ST) and whether more prolonged ST is associated with lower physical activity (PA), independent of total ST, or obesity severity.

OBJECTIVES

To characterize variability in prolonged ST among bariatric patients preoperatively and assess the importance of a "prolonger" pattern in relation to PA and weight status.

SETTING

Two university hospital clinics, United States.

METHODS

Adult patients (n = 76) wore a wrist-based accelerometer for 10 days preoperatively. ST and time spent in light and moderate-to-vigorous PA was determined using validated thresholds. Percent of total ST accumulated in ≥30-consecutive ST minute bouts was calculated, and participants were trichotomized into low, medium, and high "prolongers" based on this value. The associations of prolonged ST with PA and obesity were examined.

RESULTS

On average, participants accumulated a mean ± standard deviation of 10.5 ± 2.1 hours of ST per day, 30% of which was prolonged (prolonger groups: low = 7.2%-24.5%, medium = 24.5%-33.0%, and high = 34.0%-52.6% of ST in ≥30-min bouts). Adjusting for covariates including total ST, high prolongers had fewer light PA minutes per day (P < .01), and a greater percentage of prolonged ST related to lower likelihood of meeting the national guideline of ≥150 moderate-to-vigorous PA minutes per week (P = .012). High (versus low) prolongers had more severe obesity (P < .05).

CONCLUSIONS

Accumulating a greater percentage of ST in prolonged bouts appears to be adversely related to PA and obesity severity among bariatric patients. Future research should determine whether interrupting prolonged ST with brief breaks can favorably modify PA and weight in this population.

Physical Activity and the Prevention of Weight Gain in Adults: A Systematic Review

PURPOSE

To conduct a systematic literature review to determine if physical activity is associated with prevention of weight gain in adults.

METHODS

The primary literature search was conducted for the 2018 Physical Activity Guidelines Advisory Committee and encompassed literature through June 2017, with an additional literature search conducted to include literature published through March 2018 for inclusion in this systematic review.

RESULTS

The literature review identified 40 articles pertinent to the research question. There is strong evidence of an association between physical activity and prevention of weight gain in adults, with the majority of the evidence from prospective cohort studies. Based on limited evidence in adults, however, there is a dose-response relationship and the prevention of weight gain is most pronounced when moderate-to-vigorous intensity physical activity (≥3 METs) is above 150 min·wk. Although there is strong evidence to demonstrate that the relationship between greater time spent in physical activity and attenuated weight gain in adults is observed with moderate-to-vigorous intensity physical activity, there is insufficient evidence available to determine if there is an association between light-intensity activity (<3 METs) and attenuated weight gain in adults.

CONCLUSIONS

The scientific evidence supports that physical activity can be an effective lifestyle behavior to prevent or minimize weight gain in adults. Therefore, public health initiatives to prevent weight gain, overweight, and obesity should include physical activity as an important lifestyle behavior.

Physical Activity in the Prevention of Weight Gain: the Impact of Measurement and Interpretation of Associations

PURPOSE OF REVIEW

To what extent do different methods of physical activity measurement and statistical analysis influence the reported associations between physical activity and weight gain?

RECENT FINDINGS

The obesity epidemic has led to a focus on lifestyle approaches to the prevention of weight gain. Physical activity is one such approach. A number of studies have reported beneficial associations between higher levels of physical activity and weight gain at the population level. However, limitations of physical activity measurement and analytical models in some of these studies are likely to have resulted in overestimation of the strength of association. Understanding the limitations of assessment methods and analytical models used in epidemiological research should facilitate more realistic appraisal for physical activity to prevent weight gain at the population level and inform approaches to future research.

The impact of gynaecological cancer treatment on physical activity levels: a systematic review of observational studies

BACKGROUND

The natural history of physical activity levels during and following gynaecological cancer treatment is not well understood. This is required in order to establish the time at which physical activity levels are lowest in order to target cancer rehabilitation or exercise interventions in gynaecological cancer population accordingly.

OBJECTIVES

To conduct a systematic review to evaluate the impact of gynaecological cancer treatments on physical activity levels and to summarise the pattern of changes in physical activity levels over time among patients with gynaecological cancer.

METHODS

A comprehensive literature search was performed via MEDLINE (1946-2018), CINAHL (1982-2018), EMBASE (1947-2018), Ovid Emcare (1947-2018), PsycINFO (1806-2018) and the Cochrane Library (1991-2018). Studies were eligible for inclusion if they had assessed changes in physical activity levels during and after gynaecological cancer treatment. The methodological quality of the eligible studies was assessed by two independent reviewers using the Joanna Briggs Institute Critical Appraisal Tools.

RESULTS

In total, six studies (three cohort studies and three cross-sectional studies) with 1607 participants were included. All studies used patient-reported physical activity measures. Two of the three cohort studies measured patient-recalled physical activity levels before diagnosis (baseline), and length of follow-up varied across all studies. The majority of participants were treated surgically±adjuvant therapy. Physical activity levels decreased at 6 months following surgery when compared with pre-treatment levels. Approximately 91% of participants did not meet physical activity guidelines 2 years following diagnosis, and 58% reported being less physically active 3 years after diagnosis, compared with the pre-diagnosis levels.

CONCLUSIONS

Despite the paucity of evidence and limitations in the current body of literature, this review demonstrated that compared to pre-diagnosis, levels of physical activity remain low in gynaecological cancer survivors up to 3 years after diagnosis. More research is warranted to better characterise the pattern of change of physical activity levels across the disease trajectory and identify changes in physical activity patterns by cancer treatments and gynaecological tumour streams in order to target interventions accordingly.

Revisiting the evolutionary origins of obesity: lazy versus peppy-thrifty genotype hypothesis

The recent global obesity epidemic is attributed to major societal and environmental changes, such as excessive energy intake and sedentary lifestyle. However, exposure to 'obesogenic' environments does not necessarily result in obesity at the individual level, as 40-75% of body mass index variation in population is attributed to genetic differences. The thrifty genotype theory posits that genetic variants promoting efficient food sequestering and optimal deposition of fat during periods of food abundance were evolutionarily advantageous for the early hunter-gatherer and were positively selected. However, the thrifty genotype is likely too simplistic and fails to provide a justification for the complex distribution of obesity predisposing gene variants and for the broad range of body mass index observed in diverse ethnic groups. This review proposes that gene pleiotropy may better account for the variability in the distribution of obesity susceptibility alleles across modern populations. We outline the lazy-thrifty versus peppy-thrifty genotype hypothesis and detail the body of evidence in the literature in support of this novel concept. Future population genetics and mathematical modelling studies that account for pleiotropy may further improve our understanding of the evolutionary origins of the current obesity epidemic.

The association between sedentary behaviors during weekdays and weekend with change in body composition in young adults

BACKGROUND

High sedentary time has been considered an important chronic disease risk factor but there is only limited information on the association of specific sedentary behaviors on weekdays and weekend-days with body composition. The present study examines the prospective association of total sedentary time and specific sedentary behaviors during weekdays and the weekend with body composition in young adults.

METHODS

A total of 332 adults (50% male; 27.7 ± 3.7 years) were followed over a period of 1 year. Time spent sedentary, excluding sleep (SED), and in physical activity (PA) during weekdays and weekend-days was objectively assessed every 3 months with a multi-sensor device over a period of at least 8 days. In addition, participants reported sitting time, TV time and non-work related time spent at the computer separately for weekdays and the weekend. Fat mass and fat free mass were assessed via dual x-ray absorptiometry and used to calculate percent body fat (%BF). Energy intake was estimated based on TDEE and change in body composition.

RESULTS

Cross-sectional analyses showed a significant correlation between SED and body composition (0.18 ≤ r ≤ 0.34). Associations between body weight and specific sedentary behaviors were less pronounced and significant during weekdays only (r ≤ 0.16). Nevertheless, decrease in SED during weekends, rather than during weekdays, was significantly associated with subsequent decrease in %BF (β = 0.06, p <0.01). After adjusting for PA and energy intake, results for SED were no longer significant. Only the association between change in sitting time during weekends and subsequent %BF was independent from change in PA or energy intake (β%BF = 0.04, p = 0.01), while there was no significant association between TV or computer time and subsequent body composition.

CONCLUSIONS

The stronger prospective association between sedentary behavior during weekends with subsequent body composition emphasizes the importance of leisure time behavior in weight management.

The mysterious case of the public health guideline that is (almost) entirely ignored: call for a research agenda on the causes of the extreme avoidance of physical activity in obesity

Physical activity and exercise guidelines for weight management call for at least 60 min of daily activity. However, these documents fail to acknowledge that almost no obese adults meet this target and that non-adherence and dropout are even higher among obese individuals than the general population. The reasons for this level of activity avoidance among obese individuals remain poorly understood, and there are no evidence-based methods for addressing the problem. Opinions among exercise scientists are polarized. Some advocate moderate intensity and long duration, whereas others call for high intensity and shorter duration. The latter approach attributes the inactivity and high dropout to limited discretionary time and the slow accrual of visible benefits. However, higher intensity has been associated with non-adherence and dropout, whereas longer duration has not. A conceptual model is then proposed, according to which obesity interacts with intensity, causing physical activity and exercise to be associated with reduced pleasure among obese individuals. We theorize that, in turn, repeated experiences of reduced pleasure lead to avoidance. On this basis, we call for a research agenda aimed at identifying the causes of activity-associated and exercise-associated displeasure in obesity and, by extension, the causes of the extreme physical inactivity among obese individuals.

Objectively Quantified Physical Activity and Sedentary Behavior in Predicting Visceral Adiposity and Liver Fat

Objective. Epidemiologic studies suggest an inverse relationship between nonalcoholic fatty liver disease (NAFLD), visceral adipose tissue (VAT), and self-reported physical activity levels. However, subjective measurements can be inaccurate and prone to reporter bias. We investigated whether objectively quantified physical activity levels predicted liver fat and VAT in overweight/obese adults. Methods. Habitual physical activity was measured by triaxial accelerometry for four days (n = 82). Time spent in sedentary behavior (MET < 1.6) and light (MET 1.6 < 3), moderate (MET 3 < 6), and vigorous (MET 6 < 9) physical activity was quantified. Magnetic resonance imaging and spectroscopy were used to quantify visceral and liver fat. Bivariate correlations and hierarchical multiple regression analyses were performed. Results. There were no associations between physical activity or sedentary behavior and liver lipid. Sedentary behavior and moderate and vigorous physical activity accounted for just 3% of variance for VAT (p = 0.14) and 0.003% for liver fat (p = 0.96). Higher levels of VAT were associated with time spent in moderate activity (r = 0.294, p = 0.007), but there was no association with sedentary behavior. Known risk factors for obesity-related NAFLD accounted for 62% and 40% of variance in VAT and liver fat, respectively (p < 0.01). Conclusion. Objectively measured levels of habitual physical activity and sedentary behavior did not influence VAT or liver fat.

Prospective relationships between body weight and physical activity: an observational analysis from the NAVIGATOR study

OBJECTIVES

While bidirectional relationships exist between body weight and physical activity, direction of causality remains uncertain and previous studies have been limited by self-reported activity or weight and small sample size. We investigated the prospective relationships between weight and physical activity.

DESIGN

Observational analysis of data from the Nateglinide And Valsartan in Impaired Glucose Tolerance Outcomes Research (NAVIGATOR) study, a double-blinded randomised clinical trial of nateglinide and valsartan, respectively.

SETTING

Multinational study of 9306 participants.

PARTICIPANTS

Participants with biochemically confirmed impaired glucose tolerance had annual measurements of both weight and step count using research grade pedometers, worn for 7 days consecutively. Along with randomisation to valsartan or placebo plus nateglinide or placebo, participants took part in a lifestyle modification programme.

OUTCOME MEASURES

Longitudinal regression using weight as response value and physical activity as predictor value was conducted, adjusted for baseline covariates. Analysis was then repeated with physical activity as response value and weight as predictor value. Only participants with a response value preceded by at least three annual response values were included.

RESULTS

Adequate data were available for 2811 (30%) of NAVIGATOR participants. Previous weight (χ(2)=16.8; p<0.0001), but not change in weight (χ(2)=0.1; p=0.71) was inversely associated with subsequent step count, indicating lower subsequent levels of physical activity in heavier individuals. Change in step count (χ(2)=5.9; p=0.02) but not previous step count (χ(2)=0.9; p=0.34) was inversely associated with subsequent weight. However, in the context of trajectories already established for weight (χ(2) for previous weight measurements 747.3; p<0.0001) and physical activity (χ(2) for previous step count 432.6; p<0.0001), these effects were of limited clinical importance.

CONCLUSIONS

While a prospective bidirectional relationship was observed between weight and physical activity, the magnitude of any effect was very small in the context of natural trajectories already established for these variables.

TRIAL REGISTRATION NUMBER

NCT00097786.

Midlife determinants associated with sedentary behavior in old age

BACKGROUND

Sedentary behavior is associated with adverse health effects. Insights into associated determinants are essential to prevent sedentary behavior and limit health risks. Sedentary behavior should be viewed as a distinct health behavior; therefore, its determinants should be independently identified.

PURPOSE

This study examines the prospective associations between a wide range of midlife determinants and objectively measured sedentary time in old age.

METHODS

Data from 565 participants (age 73-92 yr) of the AGESII-Reykjavik Study were used. Participants wore an accelerometer (ActiGraph GT3X) on the right hip for seven consecutive days. On average, 31 yr earlier (during midlife), demographic, socioeconomic, lifestyle, and biomedical factors were collected. Linear regression models were used to examine prospective associations between midlife determinants and sedentary time (<100 counts per minute) in old age.

RESULTS

After adjustment for sex, age, follow-up time, minutes of moderate to vigorous physical activity, body mass index, health status, mobility limitation, and joint pain in old age, the midlife determinants not being married, primary education, living in a duplex or living in an apartment (vs villa), being obese, and having a heart disease were associated with, on average, 15.3, 12.4, 13.5, 13.3, 21.8, and 38.9 sedentary minutes more per day in old age, respectively.

CONCLUSIONS

This study shows that demographic, socioeconomic, and biomedical determinants in midlife were associated with considerably more sedentary time per day in old age. These results can indicate the possibility of predicting sedentariness in old age, which could be used to identify target groups for prevention programs reducing sedentary time in older adults.

Physical activity, sedentary time and gain in overall and central body fat: 7-year follow-up of the ProActive trial cohort

OBJECTIVE

The objective of this study is to examine the independent associations of time spent in moderate-to-vigorous physical activity (MVPA) and sedentary (SED-time), with total and abdominal body fat (BF), and the bidirectionality of these associations in adults at high risk of type 2 diabetes.

DESIGN AND SUBJECTS

We measured MVPA (min per day) and SED-time (h per day) by accelerometry, and indices of total (body weight, fat mass (FM), BF% and FM index) and abdominal BF (waist circumference (WC)) using standard procedures in 231 adults (41.3 ± 6.4 years) with parental history of type 2 diabetes (ProActive UK) at baseline, 1-year and 7-year follow-up. Mixed effects models were used to quantify the independent associations (expressed as standardised β-coefficients (95% confidence interval (CI))) of MVPA and SED-time with fat indices, using data from all three time points. All models were adjusted for age, sex, intervention arm, monitor wear time, follow-up time, smoking status, socioeconomic status and MVPA/SED-time.

RESULTS

MVPA was inversely and independently associated with all indices of total BF (for example, 1 s.d. higher MVPA was associated with a reduction in FM, β = -0.09 (95% CI: -0.14, -0.04) s.d.) and abdominal BF (for example, WC: β = -0.07 (-0.12, -0.02)). Similarly, higher fat indices were independently associated with a reduction in MVPA (for example, WC: β = -0.25 (-0.36, -0.15); FM: β = -0.27 (-0.36, -0.18)). SED-time was positively and independently associated with most fat indices (for example, WC: β = 0.03 (-0.04, 0.09); FM: β = 0.10 (0.03, 0.17)). Higher values of all fat indices independently predicted longer SED-time (for example, WC: β = 0.10 (0.02, 0.18), FM: β = 0.15 (0.07, 0.22)).

CONCLUSIONS

The associations of MVPA and SED-time with total and abdominal BF are bidirectional and independent among individuals at high risk for type 2 diabetes. The association between BF and MVPA is stronger than the reciprocal association, highlighting the importance of considering BF as a determinant of decreasing activity and a potential consequence. Promoting more MVPA and less SED-time may reduce total and abdominal BF.

Achievement of public health recommendations for physical activity and prevention of gains in adiposity in adults

Physical activity (PA) is considered a cornerstone in weight control and public health guidelines recommend regular participation to prevent gains in adiposity. It may therefore come as a surprise that the cumulative evidence from observational studies to support this is not strong. A weakness of many published observational studies on this topic has been a reliance on a single baseline assessment of PA. Using only the baseline information on PA in a prospective study cause misclassification because of participants often change activity level during follow-up. In turn this causes regression dilution bias and decreases the precision of the estimate of an association between PA and adiposity. Furthermore, because gains in adiposity often are caused by a small average daily energy imbalance over many years, following individuals for longer periods of time is essential to characterize a relationship.

Obesity increases risk of declining physical activity over time in women: a prospective cohort study

OBJECTIVE

Research indicates that risk of obesity increases as physical activity (PA) decreases; however, the reciprocal effect has been rarely studied. The present investigation was conducted to determine the contribution of obesity on objectively measured PA over 20 months.

DESIGN AND METHODS

A prospective cohort design with 254 middle-aged women was employed. Body fat percentage (BF%) was measured using Bod Pod, and obesity was defined as BF% ≥32%. PA was assessed objectively using 7-day accelerometry at baseline and ∼20 months later at follow-up.

RESULTS

Of the 254 subjects, 124 were obese (49%) at baseline. Mean BF% was 32.1 ± 7.8 and average age was 41.7 ± 3.1 years. Mean weekly PA was 2.79 ± 0.85 million activity counts for all participants. Over the 20-month period, PA decreased significantly more in obese women (-8.1% ± 27.1%) than in nonobese women (0.3% ± 31.7%) after adjusting for confounders (F = 5.3, P = 0.022). Moderate plus vigorous PA levels also decreased more in obese women (-28.1 ± 73.6 min/week) than in nonobese women (-5.9 ± 66.8 min/week), after adjusting for covariates (F = 7.84; P = 0.0055).

CONCLUSIONS

It appears that obese women tend to reduce PA over time at a faster rate than nonobese women. Evidently, obesity is a risk factor for decreasing PA over time in middle-aged women.

Consistency and timing of marital transitions and survival during midlife: the role of personality and health risk behaviors

BACKGROUND

Marital status is associated with survival.

PURPOSE

The aims of this study are to evaluate marital history and timing on mortality during midlife, test the role of pre-marital personality, and quantify the role of health risk behaviors.

METHODS

Cox proportional hazard models were run with varying classifications of marital history and sets of covariates.

RESULTS

In fully adjusted models compared to the currently married, lifetime marital history predicts premature mortality with never married at 2.33 times risk of death and ever married at 1.64 risk of death. Midlife marital history shows that not having a partner during midlife (hazard ratio (HR) = 3.10 formerly married; HR = 2.59 remaining single) has the highest risk of death. Controlling for personality and health risk behaviors reduces but does not eliminate the impact of marital status.

CONCLUSION

Consistency of marital status during midlife suggests that lack of a partner is associated with midlife mortality.

Comparison of BMI and physical activity between old order Amish children and non-Amish children

OBJECTIVE

The Old Order Amish (OOA) is a conservative Christian sect of European origin living in Pennsylvania. Diabetes is rare in adult OOA despite a mean BMI rivaling that in the general U.S. non-Hispanic white population. The current study examines childhood factors that may contribute to the low prevalence of diabetes in the OOA by comparing OOA children aged 8-19 years with National Health and Nutrition Examination Survey (NHANES) data and children from Maryland's Eastern Shore (ES), a nearby, non-Amish, rural community. We hypothesized that pediatric overweight is less common in OOA children, that physical activity (PA) and BMI are inversely correlated, and that OOA children are more physically active than ES children.

RESEARCH DESIGN AND METHODS

We obtained anthropometric data in 270 OOA children and 229 ES children (166 non-Hispanic white, 60 non-Hispanic black, 3 Hispanic). PA was measured by hip-worn accelerometers in all ES children and in 198 OOA children. Instrumentation in 43 OOA children was identical to ES children.

RESULTS

OOA children were approximately 3.3 times less likely than non-Hispanic white ES children and NHANES estimates to be overweight (BMI ≥85th percentile, Centers for Disease Control and Prevention). Time spent in moderate/vigorous PA (MVPA) was inversely correlated to BMI z-score (r = -0.24, P = 0.0006). PA levels did not differ by ethnicity within the ES group, but OOA children spent an additional 34 min/day in light activity (442 ± 56 vs. 408 ± 75, P = 0.005) and, impressively, an additional 53 min/day in MVPA (106 ± 54 vs. 53 ± 32, P < 0.0001) compared with ES children. In both groups, boys were more active than girls but OOA girls were easily more active than ES boys.

CONCLUSIONS

We confirmed all three hypotheses. Together with our previous data, the study implies that the OOA tend to gain their excess weight relatively late in life and that OOA children are very physically active, both of which may provide some long-term protection against diabetes.

Rate of weight gain predicts change in physical activity levels: a longitudinal analysis of the EPIC-Norfolk cohort

OBJECTIVE

To investigate the relationship of body weight and its changes over time with physical activity (PA).

DESIGN

Population-based prospective cohort study (Norfolk cohort of the European Prospective Investigation into Cancer and Nutrition, EPIC-Norfolk, United Kingdom).

SUBJECTS

A total of 25 639 men and women aged 39-79 years at baseline. PA was self-reported. Weight and height were measured by standard clinical procedures at baseline and self-reported at 18-month and 10-year follow-ups (calibrated against clinical measures). Main outcome measure was PA at the 10-year follow-up.

RESULTS

Body weight and PA were inversely associated in cross-sectional analyses. In longitudinal analyses, an increase in weight was associated with higher risk of being inactive 10 years later, after adjusting for baseline activity, 18-month activity, sex, baseline age, prevalent diseases, socioeconomic status, education, smoking, total daily energy intake and alcohol intake. Compared with stable weight, a gain in weight of >2 kg per year in the short-, medium- and long-term was consistently and significantly associated with greater likelihood of physical inactivity after 10 years, with the most pronounced effect for long-term weight gain, OR=1.89 (95% CI: 1.30-2.70) in fully adjusted analysis. Weight gain of 0.5-2 kg per year over long-term was substantially associated with physical inactivity after full adjustment, OR=1.26 (95% CI: 1.11-1.41).

CONCLUSION

Weight gain (during short-, medium- and long-term) is a significant determinant of future physical inactivity independent of baseline weight and activity. Compared with maintaining weight, moderate (0.5-2 kg per year) and large weight gain (>2 kg per year) significantly predict future inactivity; a potentially vicious cycle including further weight gain, obesity and complications associated with a sedentary lifestyle. On the basis of current predictions of obesity trends, we estimate that the prevalence of inactivity in England would exceed 60% in the year 2020.

Chronic disease and sitting time in middle-aged Australian males: findings from the 45 and Up Study

Background

Compared to females, males experience a range of health inequities including higher rates of diabetes and cardiovascular disease. Although sitting time is emerging as a distinct risk factor for chronic disease, research on the association of sitting time and chronic disease in middle-aged Australian males is limited.

Methods

A sample of 63,048 males aged 45-64 years was drawn from the baseline dataset of the 45 and Up Study – a longitudinal cohort study on healthy ageing with 267,153 participants from across New South Wales, Australia’s most populous state. Baseline data on self-reported chronic disease (heart disease, cancer, diabetes, high blood pressure, combined chronic diseases), sitting time, physical activity (Active Australia Survey), and a range of covariates were used for cross-sectional analyses. Crude (OR), partially and fully adjusted odds ratios (AOR) and 95% confidence intervals (CI) were calculated using binary logistic regression.

Results

Compared to those sitting <4 hours/day, participants reporting 4 to <6, 6 to <8, and ≥8 hours were significantly more likely to report ever having any chronic disease (AOR 1.06, 95% CI 1.00 – 1.12, p = 0.050; AOR 1.10, 95% CI 1.03 – 1.16, p = 0.003; AOR 1.09, 95% CI 1.03 – 1.15, p = 0.002, respectively). Participants who reported 6 to <8 hours and ≥8 hours of sitting were also significantly more likely to report ever having diabetes than those reporting <4 hours/day (AOR 1.15, 95% CI 1.03 – 1.28, p = 0.016; AOR 1.21, 95% CI 1.09 – 1.33, p <0.001, respectively).

Conclusions

Our findings suggest that higher volumes of sitting time are significantly associated with diabetes and overall chronic disease, independent of physical activity and other potentially confounding factors. Prospective studies using valid and reliable measures into domain-specific sitting time in middle-aged males are required to understand and explain the direction of these relationships.

Sitting behavior and obesity: evidence from the Whitehall II study

BACKGROUND

Prospective studies report associations between indicators of time spent sitting and obesity risk. Most studies use a single indicator of sedentary behavior and are unable to clearly identify whether sedentary behavior is a cause or a consequence of obesity.

PURPOSE

To investigate cross-sectional and prospective associations between multiple sitting time indicators and obesity and examine the possibility of reverse causality.

METHODS

Using data from the Whitehall II cohort, multiple logistic models were fitted to examine associations between prevalent obesity (BMI ≥30) at Phase 5 (1997-1999), and incident obesity between Phases 5 and 7 (2003-2004) across four levels of five sitting exposures (work sitting, TV viewing, non-TV leisure-time sitting, leisure-time sitting, and total sitting). Using obesity data from three prior phases (1985-1988, 1991-1993; and recalled weight at age 25 years), linear regression models were fitted to examine the association between prior obesity and sitting time at Phase 5. Analyses were conducted in 2012.

RESULTS

None of the sitting exposures were associated with obesity either cross-sectionally or prospectively. Obesity at one previous measurement phase was associated with a 2.43-hour/week (95% CI=0.07, 4.78) increase in TV viewing; obesity at three previous phases was associated with a 7.42-hour/week (95% CI=2.7, 12.46) increase in TV-viewing hours/week at Phase 5.

CONCLUSIONS

Sitting time was not associated with obesity cross-sectionally or prospectively. Prior obesity was prospectively associated with time spent watching TV per week but not other types of sitting.

Endurance training per se increases metabolic health in young, moderately overweight men

Health benefits of physical activity may depend on a concomitant weight loss. In a randomized, controlled trial, we compared the effects of endurance training with or without weight loss to the effect of weight loss induced by an energy-reduced diet in 48 sedentary, moderately overweight men who completed a 12-week intervention program of training (T), energy-reduced diet (D), training and increased diet (T-iD), or control (C). An energy deficit of 600 kcal/day was induced by endurance training or diet in T and D and a similar training regimen plus an increased dietary intake of 600 kcal/day defined the T-iD group. Primary end point was insulin sensitivity as evaluated by HOMA-IR (mainly reflecting hepatic insulin sensitivity) and hyperinsulinemic, isoglycemic clamps (primarily reflecting peripheral insulin sensitivity). Body mass decreased in T and D by 5.9 ± 0.7 and 5.3 ± 0.7 kg, respectively, whereas T-iD and C remained weight stable. Total and abdominal fat mass were reduced in an additive manner in the T-iD, D, and T groups by 1.9 ± 0.3/0.2 ± 0.1, 4.4 ± 0.7/0.5 ± 0.1, and 7.7 ± 0.8/0.9 ± 0.1 kg, respectively. HOMA-IR was improved in T, D, and T-iD, whereas insulin-stimulated glucose clearance and suppression of plasma nonesterified fatty acids (NEFAs) were increased only in the two training groups. Thus, loss of fat mass (diet or training induced) improves hepatic insulin sensitivity, whereas peripheral insulin sensitivity in skeletal muscle and adipose tissue is increased by endurance training only. This demonstrates that endurance training per se increases various metabolic health parameters and that endurance training should preferably always be included in any intervention regimen for improving metabolic health in moderately overweight men.

Association of smoking, physical activity, and dietary habits with socioeconomic variables: a cross-sectional study in adults on both sides of the Hungarian-Romanian border

Background

The association between socioeconomic status and health-related behaviours has been clarified in several epidemiological studies. The aim of this study was to reveal the socioeconomic differences in health-related behaviours and in nutritional status of Hungarian and Romanian citizens living on both sides of the border.

Methods

A cross-sectional study based on interviewer-administered questionnaires was conducted on both sides of the Hungarian-Romanian border. The survey was completed by 1, 099 Hungarians (Hu) and 852 Romanians (Ro) aged 18 years and over; the overall participation rate was 92.9%. Demographic and socioeconomic factors, health-related behaviours (smoking, dietary habits and physical activity), body weight and height were recorded. All analyses were performed separately for Hungarians and Romanians. Simple descriptive statistics and logistic regression models were used to measure the associations between socioeconomic status and behaviour, as well as obesity.

Results

The prevalence of smoking was similar in Hungarians and Romanians (33.2% and 36.4%). The frequency of "unhealthy diet" was 70.6% in Hungarians and 75.2% in Romanians. Physical inactivity was more prevalent in Romanians (73.2%) than in Hungarians (32.0%), while the prevalence of obesity was higher in Hungarians (22.0%) than in Romanians (16.5%). Based on the univariate logistic regression models the risk of smoking was higher among those with medium educational level (ORHu = 1.66) and poor financial conditions (ORHu = 3.13) in Hungarians. The risk of unhealthy diet was higher among the low educated (ORHu = 1.77; ORRo = 7.91) and among those with poor financial conditions (ORHu = 2.05; ORRo = 4.25). None of the socioeconomic factors was associated with leisure time physical inactivity. In the multivariate models obesity was associated with medium level of education in Hungarians, and with unhealthy diet in Romanians (ORRo = 2.10). Physically inactive Hungarians were more (ORHu = 1.74), whereas inactive Romanians were less (ORRo = 0.64) likely to be obese than physically active people from the same country.

Conclusions

The present study shows that socioeconomic status is associated with health-related behaviours in a small area of Hungary and Romania. The results highlight the need for developing interventional strategies, focusing more on people in lower socioeconomic status, in order to reduce the existing inequalities in health and health-related behaviours.

Gait and Function in Class III Obesity

Walking, more specifically gait, is an essential component of daily living. Walking is a very different activity for individuals with a Body Mass Index (BMI) of 40 or more (Class III obesity) compared with those who are overweight or obese with a BMI between 26-35. Yet all obesity weight classes receive the same physical activity guidelines and recommendations. This observational study examined the components of function and disability in a group with Class III obesity and a group that is overweight or has Class I obesity. Significant differences were found between the groups in the areas of gait, body size, health condition, and activity capacity and participation. The Timed Up and Go test, gait velocity, hip circumference, and stance width appear to be most predictive of activity capacity as observed during gait assessment. The findings indicate that Class III-related gait is pathologic and not a normal adaptation.

[Frailty: a phenotype under review]

A person's biological condition in old age partly depends on previous lifestyles. Consequently, the relationship between physical activity and obesity is emerging as an important risk factor for frailty, especially due to the resulting chronic inflammatory state. This inflammation not only leads to sarcopenia, which is basic to the development of frailty, but also affects the vascular and central nervous systems. Therefore, we believe that these two systems should be included in the frailty phenotype. Under these premises, and using the data from the Toledo Study for Healthy Aging, we propose that the frailty phenotype be extended and recommend the use of a scale to evaluate the frailty trait.

Relationship of obesity to physical activity, domestic activities, and sedentary behaviours: cross-sectional findings from a national cohort of over 70,000 Thai adults

BACKGROUND

Patterns of physical activity (PA), domestic activity and sedentary behaviours are changing rapidly in Asia. Little is known about their relationship with obesity in this context. This study investigates in detail the relationship between obesity, physical activity, domestic activity and sedentary behaviours in a Thai population.

METHODS

74,981 adult students aged 20-50 from all regions of Thailand attending the Sukhothai Thammathirat Open University in 2005-2006 completed a self-administered questionnaire, including providing appropriate self-reported data on height, weight and PA. We conducted cross-sectional analyses of the relationship between obesity, defined according to Asian criteria (Body Mass Index (BMI) ≥25), and measures of physical activity and sedentary behaviours (exercise-related PA; leisure-related computer use and television watching ("screen-time"); housework and gardening; and sitting-time) adjusted for age, sex, income and education and compared according to a range of personal characteristics.

RESULTS

Overall, 15.6% of participants were obese, with a substantially greater prevalence in men (22.4%) than women (9.9%). Inverse associations between being obese and total weekly sessions of exercise-related PA were observed in men, with a significantly weaker association seen in women (p(interaction) < 0.0001). Increasing obesity with increasing screen-time was seen in all population groups examined; there was an overall 18% (15-21%) increase in obesity with every two hours of additional daily screen-time. There were 33% (26-39%) and 33% (21-43%) reductions in the adjusted risk of being obese in men and women, respectively, reporting housework/gardening daily versus seldom or never. Exercise-related PA, screen-time and housework/gardening each had independent associations with obesity.

CONCLUSIONS

Domestic activities and sedentary behaviours are important in relation to obesity in Thailand, independent of exercise-related physical activity. In this setting, programs to prevent and treat obesity through increasing general physical activity need to consider overall energy expenditure and address a wide range of low-intensity high-volume activities in order to be effective.

Abdominal obesity, TV-viewing time and prospective declines in physical activity

OBJECTIVE

To examine the prospective associations of baseline abdominal obesity and TV-viewing time with five-year reductions in leisure-time physical activity level.

METHODS

We used data from the Australian Diabetes, Obesity and Lifestyle Study (AusDiab), a nationally representative population-based cohort study with measures collected in 1999-2000 and 2004-2005. Abdominal obesity was determined by waist circumference and TV-viewing time and physical activity level were assessed using established interviewer-administered questionnaires.

RESULTS

Among 2,191 men and 2,650 women aged ≥ 25years, odds ratios (ORs) of 5-year reductions from sufficient to insufficient or no physical activity, and from insufficient to no physical activity were estimated with logistic regression. We adjusted for sociodemographic characteristics. The odds of reducing physical levels from baseline to the follow-up survey for obese men (34.2%) and women (38.1%), respectively were 1.40 (1.10-1.79) and 1.44 (1.16-1.80), compared to those with a normal waist circumference. Women, but not men, with higher levels of TV-viewing time had higher odds of reducing physical activity levels (8.6%; OR 1.46; 1.01-2.11), independent of abdominal obesity.

CONCLUSIONS

These findings suggest that abdominal obesity is associated with prospective reductions in physical activity level, and that high levels of TV-viewing time might have an additional adverse influence for women.

Effects of adiposity on physical activity in childhood: Iowa Bone Development Study

PURPOSE

The aim of this study was to examine whether adiposity level is associated with subsequent physical activity (PA) level in childhood.

METHODS

Study participants were 326 children participating in the Iowa Bone Development Study. PA and fat mass were measured using accelerometers and dual-energy x-ray absorptiometry (DXA) at approximately 5, 8, and 11 yr. Data for relevant variables such as parents' education and PA levels and family income were also collected. Gender-specific generalized linear models were fit to examine the association between percentage body fat (%BF) at age 8 and intensity-weighted moderate- to vigorous-intensity PA (IW-MVPA) at age 11.

RESULTS

After adjusting for IW-MVPA at age 8, the interval between the age 8 and 11 examinations, residualized change scores of %BF and IW-MVPA from age 5 to 8, and mother's education level, %BF at age 8 was negatively associated with IW-MVPA at age 11 among boys (P < 0.05). After adjusting for IW-MVPA at age 8, physical maturity, and family income, %BF at age 8 was negatively associated with IW-MVPA at age 11 among girls (P < 0.05). Categorical data analysis also showed that the odds ratio (OR) of being in the lowest quartile relative to the highest quartile of IW-MVPA at age 11 for boys and girls with high %BF at age 8 were approximately four times higher than the OR for those with low %BF at age 8 (OR = 4.38, 95% CI = 1.05-18.24 for boys; OR = 4.48, 95% CI = 1.35-14.85 for girls).

CONCLUSIONS

This study suggests that adiposity level may be a determinant of PA behavior. Specific intervention strategies for overweight children may be needed to promote PA.

[Sitting-time means and correlates in adults living in Ribeirão Preto-SP, Brazil, in 2006: OBEDIARP project]

This study aimed to estimate mean daily sitting-time and to identify correlates of sitting-time in adults living in the urban area of Ribeirão Preto-SP, in 2006. A cross-sectional population-based epidemiological study was carried out using three-stage cluster sampling. From a sample of 1,205 individuals, 930 attended the interviews. The variability introduced in the third sampling fraction was corrected by attributing sampling weights taking into account the non-response rate and the number of eligible units in each household, resulting in a weighted sample of 2,197 participants. To identify sitting time correlates, multiple linear regression models were used. The design effect was considered when calculating all estimates. The reported overall mean sitting-time/day was 280.9 minutes. In the multivariate analysis, the following correlates were kept in the final model: gender; years of education; smoking; metabolic waste (Mets* · min* · week(-1)); working/day hours, and number of familial antecedents of obesity. The results pointed out sitting-time correlates and the need for health planning related to promotion and prevention policies.

Targeting cultural changes supportive of the healthiest lifestyle patterns. A biosocial evidence-base for prevention of obesity

This paper argues that the rise in obesity can be slowed only by universal education based on a type of evidence that does not yet exist. On top of literacy and numeracy, people need the ability to preempt the fattening effect of a decrease in habitual physical activity by altering familiar patterns of eating, drinking and exercise in ways that are both maintainable within the individual's social and physical environment and also effective at decreasing weight to the asymptote for each sustained change. Hence the prevention of obesity requires locally valid evidence on which changes to specific customary habits actually do avoid unhealthy fattening. Interventions need to focus on antecedents to individuals' common lapses from the healthy changes in these customs. Yet no research has been funded into the public's descriptions of feasible changes that cause a step down in weight, let alone into the environmental conditions for individuals' maintenance of those changes. As a result, public health policies on obesity lack scientific basis. When will a start be made on systematic identification of cultural supports to readily executed patterns of lifestyle behaviour which improve health to extents that have been directly measured?

Associations between sitting time and weight in young adult Australian women

OBJECTIVE

Sedentary behaviour may be a contributor to weight gain in today's young adult women, who are gaining weight faster than women in their mothers' generation. The aim was to examine the relationships between sitting time and weight in young women.

METHOD

Data were from women born in 1973-1978 who completed surveys in 2000, 2003 and 2006 for the Australian Longitudinal Study on Women's Health. Associations between concurrent changes in sitting-time and weight, and prospective associations between these variables, were examined using ANOVA and linear regressions, stratified by BMI-category in 2000 (n=5562).

RESULTS

Among overweight and obese women, percentage weight change from 2000 to 2006 was higher in those whose sitting time increased (>20%) than in those whose sitting time decreased (>20%) over the same period (p<0.05). Conversely, percentage change in sitting time was significantly higher in those who gained weight (>5%) than in those who lost weight (>5%) (p<0.05). There were no prospective associations between (change in) sitting time and weight change, or between (change in) weight and change in sitting time.

CONCLUSION

The results confirm associations between concurrent changes in weight and changes in sitting time in overweight and obese women, but no prospective relationships were found.

Sitting time is associated with weight, but not with weight gain in mid-aged Australian women

The aim of this study was to examine the associations between sitting time, weight, and weight gain in Australian women born in 1946-1951. Data were from 8,233 women who completed surveys for the Australian Longitudinal Study on Women's Health (ALSWH) in 2001, 2004, and 2007. Associations between sitting time and weight, and between sitting time and weight change in each 3-year period were examined using repeated measures modeling. The associations between weight and change in sitting time were also examined. Analyses were stratified for BMI categories: normal weight (18.5 <or= BMI < 25), overweight (25 <or= BMI < 30), and obese (BMI >or= 30). In cross-sectional models, each additional hour of sitting time was associated with 110 g (95% confidence interval (CI): 40-180) and 260 g (95% CI: 140-380) additional weight in overweight and obese women, respectively (fully adjusted model). In prospective analyses, sitting time was not consistently associated with weight change, after adjustment for other variables, and weight was not associated with change in sitting time over successive 3-year periods. In conclusion, although the cross-sectional associations between sitting time and weight were evident in overweight and obese women, there was no consistent association between sitting time and weight gain. A potential explanation is that prospective associations may only be apparent over longer periods of time. These results do not support a role for reducing sitting time as a short-term means of weight control in mid-aged women.

Modification effects of physical activity and protein intake on heritability of body size and composition

BACKGROUND

The development of obesity is still a poorly understood process that is dependent on both genetic and environmental factors.

OBJECTIVE

The objective was to examine how physical activity and the proportion of energy as protein in the diet modify the genetic variation of body mass index (BMI), waist circumference, and percentage body fat.

DESIGN

Twins from Denmark (756 complete pairs) and Finland (278 complete pairs) aged 18-67 and 21-24 y, respectively, participated. The proportion of energy as protein in the diet was estimated by using food-frequency questionnaires. The participants reported the frequency and intensity of their leisure time physical activity. Waist circumference and BMI were measured. Percentage body fat was assessed in Denmark by using a bioelectrical impedance method. The data were analyzed by using gene-environment interaction models for twin data with the Mx statistical package (Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA).

RESULTS

High physical activity was associated with lower mean values, and a high proportion of protein in the diet was associated with higher mean BMI, waist circumference, and percentage body fat and a reduction in genetic and environmental variances. Genetic modification by physical activity was statistically significant for BMI (-0.18; 95% CI: -0.31, -0.05) and waist circumference (-0.14; 95% CI: -0.22, -0.05) in the merged data. A high proportion of protein in the diet reduced genetic and environmental variances in BMI and waist circumference in Danish men but not in women or in Finnish men.

CONCLUSIONS

Our results suggest that, in physically active individuals, the genetic variation in weight is reduced, which possibly suggests that physical activity is able to modify the action of the genes responsible for predisposition to obesity, whereas the protein content of the diet has no appreciable effect.

Factors associated with BMI change over five years in a Swedish adult population. Results from the Scania Public Health Cohort Study

OBJECTIVES

On account of the increasing worldwide problems associated with overweight and obesity, the aim of the present study was to examine BMI change over 5 years in relation to different lifestyle-, demographic- and psychosocial work-related factors.

METHODS

A cohort of 9913 persons responded to an identical survey in 2000 and 2005. BMI change over the period was examined in relation to gender, age, educational level, physical activity, job strain, and baseline BMI.

RESULTS

Mean BMI as well as prevalence of overweight and obesity increased in the cohort; most among younger persons. In all groups but younger women, BMI increase was greatest in the lowest baseline BMI quartile. Low education was associated with increased BMI at baseline, but not with BMI change over time except among young women. Exercisers had lower BMI than non-exercising persons, and exercise pattern over time was also significantly associated with BMI change. The greatest BMI increase was found among exercise drop-outs, while those who had taken up exercise during the study period were the only group who did not show a significant BMI increase over the study period. Job strain showed inconsistent associations with BMI change.

CONCLUSIONS

Although socioeconomic differences in BMI were observed, these inequalities did not appear to be increasing, except among young women. Persons with a low initial BMI increased more in weight than persons with a high initial BMI. Exercise behaviour appeared to be an important factor for maintaining, or avoiding heavy increase in, BMI.

Conference on "Multidisciplinary approaches to nutritional problems". Symposium on "Diabetes and health". Challenges in the study of causation of obesity

Use of the energy balance equation for understanding the causation of obesity is discussed. Its basis on the thermodynamic laws is expressed in mathematical models for body-weight changes. Only a very small net energy surplus per time unit constitutes the energy deposition during weight gain, making measurements of its components difficult. The physical laws provide exact quantitative relationships between energy intake, energy expenditure and deposition of energy, but cannot disentangle the initiating and driving forces of the energy imbalance, which may also be an active storage of fat in adipose tissue. These and various other limitations of the energy balance model warrant cautiousness in using the model in studies of obesity causation. Weight gain may be self-promoting and mathematical feedback models allowing estimation of such effects show that they are realistic. Predisposition and susceptibility should be distinguished, and susceptibility as a modifiable predisposition, the genetic and environmental contribution to predisposition and its usefulness as targets for prevention and treatment are discussed. Current progress in unravelling genetic predisposition, the complex genetically-determined mechanisms, the slower progress in unravelling the environmental influences, the different nature of genetic and environmental influences, the possible pathways of environmental influences and the environmental influences as mediators of genetic effects are addressed. The evidence behind the prevailing concept of the 'obesogenic' environment is critically analysed. Finally, particular opportunities for the identification of the causes of the obesity epidemic by detailed analysis of an observed irregular development of the epidemic over long time periods are presented, and evidence for predisposition as a result of postnatal environmental influences is inferred from these studies.

Time spent being sedentary and weight gain in healthy adults: reverse or bidirectional causality?

BACKGROUND

Whether obesity is a cause or a consequence of a sedentary lifestyle has not yet been fully elucidated, which leaves uncertainty about the direction of causality.

OBJECTIVE

We aimed to assess the longitudinal associations between objectively measured time spent being sedentary (sedentary time) and obesity indicators.

DESIGN

The study was a prospective, population-based cohort study in 393 middle-aged healthy whites (n = 176 M, 217 F). Sedentary time (% of daytime hours) was measured by individually calibrated monitoring of the heart rate. Body weight (BW), body mass index (BMI), and waist circumference (WC) were assessed by standard clinical procedures. Fat mass (FM) was assessed with bioimpedance. All measurements were collected at baseline and at 5.6-y follow-up.

RESULTS

At baseline, sedentary time was significantly correlated with FM (partial r = 0.10, P = 0.043) and WC (partial r = 0.11, P = 0.027) after adjustment for sex and age. At follow-up, sedentary time was significantly correlated with BW (partial r = 0.19, P < 0.0001), BMI (partial r = 0.20, P < 0.0001), WC (partial r = 0.15, P = 0.003), and FM (partial r = 0.19, P < 0.0001). Sedentary time did not predict any of the obesity indicators at follow-up. In contrast, BW (beta = 0.33; 95% CI: 0.15, 0.50), BMI (1.10; 0.58, 1.63), FM (0.59; 0.11, 0.40), and WC (0.44; 0.23, 0.66) predicted sedentary time at follow-up after adjustment for sex, baseline age, baseline sedentary time, baseline physical activity energy expenditure, and follow-up time.

CONCLUSION

BMI, FM, and WC may predict sedentary time, but our results do not suggest that sedentary time predicts future obesity.

Feedback models allowing estimation of thresholds for self-promoting body weight gain

OBJECTIVE

Most people maintain almost constant body weight over long time with varying physical activity and food intake. This indicates the existence of a regulation that works well for most individuals. Yet some people develop obesity, indicating that this regulation sometimes fails. The difference between the two situations is typically an energy imbalance of about 1% over a long period of time.

THEORY

Weight gain increases basal metabolic rate. Weight gain is often associated with a decrease in physical activity, although not to such an extent that it prevents an increase in total energy expenditure and energy intake. Dependent on the precise balance between these effects of weight gain, they may make the body weight unstable and tend to further promote weight gain. With the aim of identifying the thresholds beyond which such self-promoting weight gain may take place, we develop a simple mathematical model of the body as an energy-consuming machine in which the changes in physical activity and food intake are described as feedback effects in addition to the effect of the weight gain on basal metabolic rate. The feedback parameters of the model may differ between individuals and only in some cases do they take values that make weight gain self-promoting.

RESULTS

We determine the quantitative conditions under which body weight gain becomes self-promoting. We find that these conditions can easily be met, and that they are so small that they are not observable with currently available techniques. This phenomenon encourages emphasis on even minor changes in food intake and physical activity to abate or stop weight gain.

Mechanism by which BMI influences leisure-time physical activity behavior

OBJECTIVE

The objective of this prospective study was to clarify the mechanism by which BMI influences leisure-time physical activity. This was achieved in accordance with the assumptions underlying the Theory of Planned Behavior (TPB), considered as one of the most useful theories to predict behavior adoption.

METHODS AND PROCEDURES

At baseline, a sample of 1,530 respondents completed a short questionnaire to measure intention and perceived behavioral control (PBC), the two proximal determinants of behavior of TPB. Past behavior, sociodemographic variables, and weight and height were also assessed. The dependent variable, leisure-time physical activity was assessed 3 months later.

RESULTS

Hierarchical multiple regression analyses revealed that BMI is a direct predictor of future leisure-time physical activity, not mediated by the variables of TPB. Additional hierarchical analyses indicated that BMI was not a moderator of the intention-behavior and PBC-behavior relationships.

DISCUSSION

The results of this study suggest that high BMI is a significant negative determinant of leisure-time physical activity. This observation reinforces the importance of preventing weight gain as a health promotion strategy for avoiding a sedentary lifestyle.

Leisure-time physical activity alone may not be a sufficient public health approach to prevent obesity--a focus on China

Much small-scale research has identified the role of physical activity in obesity prevention. This is the 'energy expenditure' side of the energy balance equation. Although around half an hour of daily moderate-intensity physical activity is required for cardiovascular health and disease prevention, the quantum of physical activity required for obesity prevention and weight loss is around 60-90 minutes per day. This amount of physical activity is difficult to achieve through leisure time physical activity (LTPA) alone, and additional energy expenditure is needed in the domains of active transport, occupation activity and in domestic settings. Modeling of 24-hour energy expenditures demonstrate the need for 'active living', namely energy expenditure over and above that due to LTPA, for weight loss and obesity prevention. The consequences of this for developing countries such as China are the need to focus on preventing the declines in energy expenditure attributable to urbanization, industrialization, and motor vehicle dependence. These will pose policy challenges in the developing world, if they are to be taken seriously as obesity prevention strategies.

Moderators of the intention-behaviour and perceived behavioural control-behaviour relationships for leisure-time physical activity

BACKGROUND

Intention is a key determinant of action. However, there is a gap between intention and behavioural performance that remains to be explained. Therefore, the aim of this study was to identify moderators of the intention-behaviour and perceived behavioural control (PBC)- behaviour relationships for leisure-time physical activity.

METHOD

This was tested in reference to Ajzen's Theory of Planned Behaviour. A sample of 300 volunteers, 192 women and 108 men, aged 18 to 55, participated in the study. At baseline, the participants completed a self-administrated psychosocial questionnaire assessing Ajzen's theory variables (i.e., intention and perceived behavioural control). The behavioural measure was obtained by mail three months later.

RESULTS

Multiple hierarchical regression analyses indicated that age and annual income moderated the intention-behaviour and PBC-behaviour relationships. However, in the final model predicting behaviour (R2 = .46), only the interaction term of PBC by annual income (beta = .24, p = 0.0003) significantly contributed to the prediction of behaviour along with intention (beta = .49, p = 0.0009) and past behaviour (beta = .44, p < 0.0001).

CONCLUSION

Physical activity promotion programs would benefit not only from focusing on increasing the intention of low intenders, but also from targeting factors that moderate the perceived behavioural control-behaviour relationships.