Analiza M. Silva

Why do individuals not lose more weight from an exercise intervention at a defined dose? An energy balance analysis.

Weight loss resulting from an exercise intervention tends to be lower than predicted. Modest weight loss can arise from an increase in energy intake, physiological reductions in resting energy expenditure, an increase in lean tissue or a decrease in non‐exercise activity. Lower than expected, weight loss could also arise from weak and invalidated assumptions within predictive models. To investigate these causes, we systematically reviewed studies that monitored compliance to exercise prescriptions and measured exercise‐induced change in body composition. Changed body energy stores were calculated to determine the deficit between total daily energy intake and energy expenditures. This information combined with available measurements was used to critically evaluate explanations for low exercise‐induced weight loss. We conclude that the small magnitude of weight loss observed from the majority of evaluated exercise interventions is primarily due to low doses of prescribed exercise energy expenditures compounded by a concomitant increase in caloric intake.

Prevalence of the Portuguese Population Attaining Sufficient Physical Activity

PURPOSE Physical activity has many health benefits, and to implement strategies, mainly in those groups with insufficient levels of practice, it is important to evaluate physical activity. The main purpose of this study was to describe the prevalence of physical activity in the Portuguese population aged 10 yr and older using accelerometry. METHODS The accelerometers were worn for four consecutive days, and a valid record was defined as at least 3 d with 10 h of wear time, including one weekend day. Considering these conditions, 4696 participants were included. RESULTS According to the recommendations of 60 min·d(-1) of physical activity, 36% of participants age 10-11 yr (boys = 51.6%, girls = 22.5%) and 4% age 16-17 yr (boys = 7.9%, girls = 1.2%) were considered sufficiently active. In adulthood, ∼70% of participants age 18-64 yr (men = 76.6%, women = 65.2%) and 35% age older than 64 yr (men = 46%, women = 29%) reached the recommendation of 30 min·d(-1) of physical activity, when counting every minute of moderate or greater intensity. Considering bouts of 10 min or more of moderate or greater intensity in participants older than 17 yr, the prevalence was 4%-6% at 18-39 yr, 7%-9% at 40-64 yr, and ∼3% in persons age 65 yr or older. CONCLUSIONS The design and implementation of strategies to promote physical activity for health among children and adolescents and older adults, particularly girls/women, should be encouraged.

Validity of BMI based on self-reported weight and height in adolescents

Aim:  To assess in a subset of a nationally representative sample of Portuguese adolescents, the validity of Body Mass Index (BMI) based on self‐reported weight and height.

Prevalence of overweight and obesity among Portuguese youth: A study in a representative sample of 10–18-year-old children and adolescents

PURPOSE The aim of this research was to report the prevalence of overweight and obesity in a representative sample of Portuguese youth. METHODS This was a school-based study performed in Portugal. A total of 22 048 children and adolescents aged 10-18 years were included in the study. The World Health Organization (WHO) and the International Obesity Task Force (IOTF) cut-offs were used to categorise overweight and obese participants. RESULTS Using IOTF cut-offs the prevalence of overweight and obesity was 17.0 and 4.6% in girls, and 17.7 and 5.8% in boys, respectively (p < 0.001 for overweight and p > 0.05 for obesity), whereas WHO cut-offs resulted in overweight and obesity prevalence scores of 23.1 and 9.6% in girls, and 20.4 and 10.3% in boys, respectively (p < 0.001 for overweight and p >0.05 for obesity). With IOTF cut-offs, a lower prevalence of obesity and overweight was observed at higher ages, in both genders. With the WHO cut-offs, a lower prevalence of obesity and overweight was observed at higher ages, in boys. In girls, the prevalence of overweight and obesity increases from 10 to 12 years of age and decreases from the age of 13 to 18 years. CONCLUSION The prevalence for overweight/obesity among Portuguese children and adolescents vary according to the cut-off points used and are also of concern requiring strategies to promote healthy weight gain among children and adolescents.

Who will lose weight? A reexamination of predictors of weight loss in women

BackgroundThe purpose of this study was to analyze pretreatment predictors of short-term weight loss in Portuguese overweight and obese women involved in a weight management program. Behavioral and psychosocial predictors were selected a priori from previous results reported in American women who participated in a similar program.MethodsSubjects were 140 healthy overweight/obese women (age, 38.3 ± 5.9 y; BMI, 30.3 ± 3.7 kg/m2) who participated in a 4-month lifestyle weight loss program consisting of group-based behavior therapy to improve diet and increase physical activity. At baseline, all women completed a comprehensive behavioral and psychosocial battery, in standardized conditions.ResultsOf all starting participants, 3.5% (5 subjects) did not finish the program. By treatments end, more than half of all women had met the recomended weight loss goals, despite a large variability in individual results (range for weight loss = 19 kg). In bivariate and multivariate correlation/regression analysis fewer previous diets and weight outcome evaluations, and to a lesser extent self-motivation and body image were significant and independent predictors of weight reduction, before and after adjustment for baseline weight. A negative and slightly curvilinear relationship best described the association between outcome evaluations and weight change, revealing that persons with very accepting evaluations (that would accept or be happy with minimal weight change) lost the least amount of weight while positive but moderate evaluations of outcomes (i.e., neither low nor extremely demanding) were more predictive of success. Among those subjects who reported having initiated more than 3–4 diets in the year before the study, very few were found to be in the most successful group after treatment. Quality of life, self-esteem, and exercise variables did not predict outcomes.ConclusionsSeveral variables were confirmed as predictors of success in short-term weight loss and can be used in future hypothesis-testing studies and as a part of more evolved prediction models. Previous dieting, and pretreatment self-motivation and body image are associated with subsequent weight loss, in agreement with earlier findings in previous samples. Weight outcome evaluations appear to display a more complex relationship with treatment results and culture-specific factors may be useful in explaining this pattern of association.

Sedentary behavior and physical activity are independently related to functional fitness in older adults.

The last decades of life have been traditionally viewed as a time of inevitable disease and frailty. Sedentary living and physical activity may influence capacity to perform activities that are needed to maintain physical independence in daily living. A total of 117 males and 195 females, aged 65-103years, were assessed for physical activity and sedentary time with accelerometers and for functional fitness with the Senior Fitness Test battery. Based on the individual scores for each fitness item, a Z-score was created. Associations between functional fitness with sedentary time and moderate-to-vigorous physical activity (MVPA) were analyzed. A negative association was found between the composite Z-score for functional fitness and the sedentary time, even adjusting for MVPA and other confounders. On the other hand, MVPA was positively associated with the composite Z-score for functional fitness, independently of the sedentary time. In conclusion elderly who spend more time in physical activity or less time in sedentary behaviors exhibit improved functional fitness and other confounders. The results reinforce the importance of promoting both the reduction of sedentary behaviors and the increase of MVPA in this age group, as it may interfere at older ages in order to preserve functional fitness and performance of daily functioning tasks.

Prevalence of overweight, obesity, and abdominal obesity in a representative sample of Portuguese adults

This study determined the prevalence of overweight, obesity, and abdominal obesity in the Portuguese adults and examined the relationship between above mentioned prevalences and educational level. Body mass, stature, and waist circumference were measured in a representative sample of the Portuguese population aged 18–103 years (n = 9,447; 18–64 years: n = 6,908; ≥65 years: n = 2,539). Overweight and obesity corresponded to a body mass index ranging between 25–29.9 kg/m2 and ≥30 kg/m2, respectively. Abdominal obesity was assessed as >102 cm for males and >88 cm for females. After adjusting for educational level, the combined prevalences of overweight and obesity were 66.6% in males and 57.9% in females (18–64 years). Respective values in older adults (≥65 years) were 70.4% for males and 74.7% for females. About 19.3% of adult males and 37.9% of adult females presented abdominal obesity. Correspondent values in older adults were 32.1%, for males, and 69.7%, for females. In adults, low educational level was related to an increased risk for overweight (OR = 2.54; 95% CI: 2.08–3.09), obesity (OR = 2.76; 95% CI: 2.20–3.45), and abdominal obesity (OR = 5.48; 95% CI: 4.60–6.52). This reinforces the importance of adjusting public health strategies for educational level.

Ethnicity-related skeletal muscle differences across the lifespan

Despite research and clinical significance, limited information is available on the relations between skeletal muscle (SM) and age in adults, specifically among Hispanics, African Americans (AA), and Asians. The aim was to investigate possible sex and ethnic SM differences in adults over an age range of 60 years. Subjects were 468 male and 1280 female adults (≥18 years). SM was estimated based on DXA‐measured appendicular lean‐soft tissue using a previously reported prediction equation. Locally weighted regression smoothing lines were fit to examine SM trends and to localize age cutoffs; piecewise multiple linear regression models were then applied, controlling for weight and height, to identify age cutoffs for sex‐specific changes in SM among the ethnic groups. The age of 27 years was identified for women and men as the cut‐off after which SM starts to show a negative association with age. Both sexes had a similar ethnic pattern for expected mean SM at the age cutoff, with AA presenting the highest SM values, followed by Whites, Hispanics, and Asians. After the age cutoffs, the lowering of SM differed by ethnicity and sex: AA women showed the greatest SM lowering whereas Hispanic women had the least. Hispanic men tended to show a higher negative association of SM with age followed by AA and Whites. To conclude, significant sex and ethnic differences exist in the magnitude of negative associations of SM with age >27 years. Further studies using a longitudinal design are needed to explore the associations of ethnicity‐related decline of SM with health risks. Am. J. Hum. Biol. 2010.

Usefulness of different techniques for measuring body composition changes during weight loss in overweight and obese women

The objective was to compare measures from dual-energy X-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA) and anthropometry with a reference four-compartment model to estimate fat mass (FM) and fat-free mass (FFM) changes in overweight and obese women after a weight-loss programme. Forty-eight women (age 39.8 +/- 5.8 years; weight 79.2 +/- 11.8 kg; BMI 30.7 +/- 3.6 kg/m2) were studied in an out-patient weight-loss programme, before and after the 16-month intervention. Women attended weekly meetings for the first 4 months, followed by monthly meetings from 4 to 12 months. Body composition variables were measured by the following techniques: DXA, anthropometry (waist circumference-based model; Antrform), BIA using Tanita (TBF-310) and Omron (BF300) and a reference four-compartment model. Body weight decreased significantly ( - 3.3 (sd 3.1) kg) across the intervention. At baseline and after the intervention, FM, percentage FM and FFM assessed by Antrform, Tanita, BF300 and DXA differed significantly from the reference method (P < or = 0.001), with the exception of FFM assessed by Tanita (baseline P = 0.071 and after P = 0.007). DXA significantly overestimated the change in FM and percentage FM across weight loss ( - 4.5 v. - 3.3 kg; P 0.05) from the reference model in any body composition variables. We conclude that these methods are widely used in clinical settings, but should not be applied interchangeably to detect changes in body composition. Furthermore, the several clinical methods were not accurate enough for tracking body composition changes in overweight and obese premenopausal women after a weight-loss programme.

Body fat measurement in adolescent athletes: multicompartment molecular model comparison.

Objective:To assess the accuracy of air displacement plethysmography (ADP) and dual energy X-ray absorptiometry (DXA) per cent body fat (%BF) estimations in comparison with a reference five-compartment (5C) model used as the reference method.Design:Cross-sectional study.Setting:Outpatient University Laboratory, Lisbon, Portugal.Methods:A total of 32 girls (age: 15.1±0.3 years) and 46 boys (age: 15.3±1.2 years) athletes were measured. Body volume was assessed by ADP; bone mineral content was assessed by DXA; and total-body water was assessed by deuterium dilution. Statistical analyses included examination of the coefficient of correlation (r), standard error of estimation (s.e.e.), slope, intercept, and pure error (p.e.) and the agreement between models.Results:For boys and girls, differences between the 5C model and ADP %BF were 0.2 and 1.7% (r=0.86 and 0.98, s.e.e.=2.50 and 1.55%, p.e.=2.77 and 2.23%), respectively. Differences between the 5C model and DXA %BF were –1.0 and –3.7% (r=0.85 and 0.91, s.e.e.=2.60 and 2.91%, p.e.=2.90 and 4.66%), for boys and girls, respectively. For girls, regression between ADP and DXA against the reference method did not differ from the line of identity (P>0.05) while for boys differences were found (P<0.05). Dual energy X-ray absorptiometry overestimated %BF, particularly in girls. For both genders, large limits of agreement were found between the reference method and both techniques, with the exception of ADP in female athletes.Conclusion:We conclude that the two techniques were not precise for individual %BF prediction, though ADP revealed better agreement for girls. However, considering all performance criteria for the mean group, our analysis highlights ADP as a valid and nonbiased tool for the evaluation of body composition in adolescent athletes.