Corby K. Martin

Trends over 5 Decades in U.S. Occupation-Related Physical Activity and Their Associations with Obesity

Background The true causes of the obesity epidemic are not well understood and there are few longitudinal population-based data published examining this issue. The objective of this analysis was to examine trends in occupational physical activity during the past 5 decades and explore how these trends relate to concurrent changes in body weight in the U.S. Methodology/Principal Findings Analysis of energy expenditure for occupations in U.S. private industry since 1960 using data from the U.S. Bureau of Labor Statistics. Mean body weight was derived from the U.S. National Health and Nutrition Examination Surveys (NHANES). In the early 1960s almost half the jobs in private industry in the U.S. required at least moderate intensity physical activity whereas now less than 20% demand this level of energy expenditure. Since 1960 the estimated mean daily energy expenditure due to work related physical activity has dropped by more than 100 calories in both women and men. Energy balance model predicted weights based on change in occupation-related daily energy expenditure since 1960 for each NHANES examination period closely matched the actual change in weight for 40–50 year old men and women. For example from 1960–62 to 2003–06 we estimated that the occupation-related daily energy expenditure decreased by 142 calories in men. Given a baseline weight of 76.9 kg in 1960–02, we estimated that a 142 calories reduction would result in an increase in mean weight to 89.7 kg, which closely matched the mean NHANES weight of 91.8 kg in 2003–06. The results were similar for women. Conclusion Over the last 50 years in the U.S. we estimate that daily occupation-related energy expenditure has decreased by more than 100 calories, and this reduction in energy expenditure accounts for a significant portion of the increase in mean U.S. body weights for women and men.

Metabolic and Behavioral Compensations in Response to Caloric Restriction: Implications for the Maintenance of Weight Loss

Background Metabolic and behavioral adaptations to caloric restriction (CR) in free-living conditions have not yet been objectively measured. Methodology and Principal Findings Forty-eight (36.8±1.0 y), overweight (BMI 27.8±0.7 kg/m2) participants were randomized to four groups for 6-months; Control: energy intake at 100% of energy requirements; CR: 25% calorie restriction; CR+EX: 12.5% CR plus 12.5% increase in energy expenditure by structured exercise; LCD: low calorie diet (890 kcal/d) until 15% weight reduction followed by weight maintenance. Body composition (DXA) and total daily energy expenditure (TDEE) over 14-days by doubly labeled water (DLW) and activity related energy activity (AREE) were measured after 3 (M3) and 6 (M6) months of intervention. Weight changes at M6 were −1.0±1.1% (Control), −10.4±0.9% (CR), −10.0±0.8% (CR+EX) and −13.9±0.8% (LCD). At M3, absolute TDEE was significantly reduced in CR (−454±76 kcal/d) and LCD (−633±66 kcal/d) but not in CR+EX or controls. At M6 the reduction in TDEE remained lower than baseline in CR (−316±118 kcal/d) and LCD (−389±124 kcal/d) but reached significance only when CR and LCD were combined (−351±83 kcal/d). In response to caloric restriction (CR/LCD combined), TDEE adjusted for body composition, was significantly lower by −431±51 and −240±83 kcal/d at M3 and M6, respectively, indicating a metabolic adaptation. Likewise, physical activity (TDEE adjusted for sleeping metabolic rate) was significantly reduced from baseline at both time points. For control and CR+EX, adjusted TDEE (body composition or sleeping metabolic rate) was not changed at either M3 or M6. Conclusions For the first time we show that in free-living conditions, CR results in a metabolic adaptation and a behavioral adaptation with decreased physical activity levels. These data also suggest potential mechanisms by which CR causes large inter-individual variability in the rates of weight loss and how exercise may influence weight loss and weight loss maintenance. Trial Registration ClinicalTrials.gov NCT00099151

Effects of stevia, aspartame, and sucrose on food intake, satiety, and postprandial glucose and insulin levels.

UNLABELLED Consumption of sugar-sweetened beverages may be one of the dietary causes of metabolic disorders, such as obesity. Therefore, substituting sugar with low calorie sweeteners may be an efficacious weight management strategy. We tested the effect of preloads containing stevia, aspartame, or sucrose on food intake, satiety, and postprandial glucose and insulin levels. DESIGN 19 healthy lean (BMI=20.0-24.9) and 12 obese (BMI=30.0-39.9) individuals 18-50 years old completed three separate food test days during which they received preloads containing stevia (290kcal), aspartame (290kcal), or sucrose (493kcal) before the lunch and dinner meal. The preload order was balanced, and food intake (kcal) was directly calculated. Hunger and satiety levels were reported before and after meals, and every hour throughout the afternoon. Participants provided blood samples immediately before and 20min after the lunch preload. Despite the caloric difference in preloads (290kcal vs. 493kcal), participants did not compensate by eating more at their lunch and dinner meals when they consumed stevia and aspartame versus sucrose in preloads (mean differences in food intake over entire day between sucrose and stevia=301kcal, p<.01; aspartame=330kcal, p<.01). Self-reported hunger and satiety levels did not differ by condition. Stevia preloads significantly reduced postprandial glucose levels compared to sucrose preloads (p<.01), and postprandial insulin levels compared to both aspartame and sucrose preloads (p<.05). When consuming stevia and aspartame preloads, participants did not compensate by eating more at either their lunch or dinner meal and reported similar levels of satiety compared to when they consumed the higher calorie sucrose preload.

Profiles of sedentary behavior in children and adolescents:The US National Health and Nutrition Examination Survey, 2001-2006

OBJECTIVE To describe the prevalence of time spent in sedentary behaviors (e.g., TV/video and computer use) among youth in the US. METHODS The National Health and Nutrition Examination Survey (2001-06) provided data to examine sedentary behavior across age groups (2-5, 6-11, and 12-15 years of age), ethnic groups (European [EA], African [AA], and Mexican American [MA]), and body mass index (BMI) categories (normal weight, overweight, obese). RESULTS The sample included 8 707 (50.7% boys) children aged 2 to 15 years. Seventy percent of the sample was normal weight, 18.1% was overweight, and 11.5% was obese. The total proportion of young people engaged in TV/video viewing, computer use, and total screen time > or = 2 hours daily was 33.0%, 6.7%, and 47.3%, respectively. More boys (49.4%) than girls (45.0%); older (12-15 years: 56.0%) versus younger children (2-5 years: 35.3% and 6-11 years: 49.1%); AA (66.1%) versus EA (42.5%) and MA (46.1%); obese (58.5%) versus overweight (50.8%) versus normal weight (44.6%); and low and middle income (<

Exercise Dose and Quality of Life: A Randomized Controlled Trial

25 K: 51.4% and

Changes in Weight, Waist Circumference and Compensatory Responses with Different Doses of Exercise among Sedentary, Overweight Postmenopausal Women

25-45 K: 51.2%) versus high income (>

Effect of calorie restriction on resting metabolic rate and spontaneous physical activity.

45 K: 42.6%) children spent > or = 2 hours daily in screen time. CONCLUSION Nearly half (47%) of US children exceed > or = 2 hours/day of time in sedentary behavior. Further, it appears there are gender, age, ethnic, BMI-defined weight status, and income differences in exceeding > or = 2 hours/day in sedentary behavior. These results will be useful in planning targeted interventions at those populations with a higher prevalence of sedentary behavior.

Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating: A Randomized Controlled Trial

BACKGROUND Improved quality of life (QOL) is a purported benefit of exercise, but few randomized controlled trials and no dose-response trials have been conducted to examine this assertion. METHODS The effect of 50%, 100%, and 150% of the physical activity recommendation on QOL was examined in a 6-month randomized controlled trial. Participants were 430 sedentary postmenopausal women (body mass index range, 25.0-43.0 [calculated as weight in kilograms divided by height in meters squared]) with elevated systolic blood pressure randomized to a nonexercise control group (n = 92) or 1 of 3 exercise groups: exercise energy expenditure of 4 (n = 147), 8 (n = 96), or 12 (n = 95) kilocalories per kilogram of body weight per week. Eight aspects of physical and mental QOL were measured at baseline and month 6 with the use of the Medical Outcomes Study 36-Item Short Form Health Survey. RESULTS Change in all mental and physical aspects of QOL, except bodily pain, was dose dependent (trend analyses were significant, and exercise dose was a significant predictor of QOL change; P < .05). Higher doses of exercise were associated with larger improvements in mental and physical aspects of QOL. Controlling for weight change did not attenuate the exercise-QOL association. CONCLUSION Exercise-induced QOL improvements were dose dependent and independent of weight change.

A novel method to remotely measure food intake of free-living individuals in real time: the remote food photography method

Background It has been suggested that exercise training results in compensatory mechanisms that attenuate weight loss. However, this has only been examined with large doses of exercise. The goal of this analysis was to examine actual weight loss compared to predicted weight loss (compensation) across different doses of exercise in a controlled trial of sedentary, overweight or obese postmenopausal women (n = 411). Methodology/Principal Findings Participants were randomized to a non-exercise control (n = 94) or 1 of 3 exercise groups; exercise energy expenditure of 4 (n = 139), 8 (n = 85), or 12 (n = 93) kcal/kg/week (KKW). Training intensity was set at the heart rate associated with 50% of each womans peak VO2 and the intervention period was 6 months. All exercise was supervised. The main outcomes were actual weight loss, predicted weight loss (exercise energy expenditure/ 7700 kcal per kg), compensation (actual minus predicted weight loss) and waist circumference. The study sample had a mean (SD) age 57.2 (6.3) years, BMI of 31.7 (3.8) kg/m2, and was 63.5% Caucasian. The adherence to the intervention was >99% in all exercise groups. The mean (95% CI) weight loss in the 4, 8 and 12 KKW groups was −1.4 (−2.0, −0.8), −2.1 (−2.9, −1.4) and −1.5 (−2.2, −0.8) kg, respectively. In the 4 and 8 KKW groups the actual weight loss closely matched the predicted weight loss of −1.0 and −2.0 kg, respectively, resulting in no significant compensation. In the 12 KKW group the actual weight loss was less than the predicted weight loss (−2.7 kg) resulting in 1.2 (0.5, 1.9) kg of compensation (P<0.05 compared to 4 and 8 KKW groups). All exercise groups had a significant reduction in waist circumference which was independent of changes in weight. Conclusion In this study of previously sedentary, overweight or obese, postmenopausal women we observed no difference in the actual and predicted weight loss with 4 and 8 KKW of exercise (72 and 136 minutes respectively), while the 12 KKW (194 minutes) produced only about half of the predicted weight loss. However, all exercise groups had a significant reduction in waist circumference which was independent of changes in weight. Trial Registration ClinicalTrials.gov NCT 00011193

Leisure Time Sedentary Behavior, Occupational/Domestic Physical Activity, and Metabolic Syndrome in U.S. Men and Women

Objective: It is unclear if resting metabolic rate (RMR) and spontaneous physical activity (SPA) decrease in weight‐reduced non‐obese participants. Additionally, it is unknown if changes in SPA, measured in a respiratory chamber, reflect changes in free‐living physical activity level (PAL).