We evaluated whether the obesity-associated years of life lost (YLL) have
decreased over calendar time. We implemented a meta-analysis including only
studies with ≥2 serial BMI assessments at different calendar years. For
each BMI category (normal weight: BMI 18.5 to <25 [reference],
overweight: BMI 25 to <30, grade 1 obesity: BMI 30 to <35, and
grade 2–3 obesity: BMI ≥35), we estimated the YLL change between
1970 and 1990. Due to low sample sizes for blacks, results are reported on
whites. Among men aged≤60 years YLL for grade 1 obesity increased by
0.72 years (p<0.001) and by 1.02 years (p=0.01) for grade 2–3
obesity. For men aged>60, YLL for grade 1 obesity decreased by 1.02
years (p<0.001), and increased by 0.63 years for grade 2–3
obesity (p=0.63). Among women aged≤60, YLL for grade 1 obesity decreased
by 4.21years (p<0.001) and by 4.97 years (p<0.001) for grade
2–3 obesity. In women aged>60, YLL for grade 1 obesity decreased
by 3.98 years (p<0.001) and by 2.64 years (p=0.001) for grade
2–3 obesity. Grade 1 obesity’s association with decreased
longevity has reduced for older white men. For white women, there is evidence of
a decline in the obesity YLL association across all ages.
Body mass index (BMI); years of life lost (YLL); parametric survival; meta-analysis; calendar time; maturation; recency; length of follow-up; study-level variation; recency
Energy intake (EI) and physical activity energy expenditure (PAEE) are key modifiable determinants of energy balance, traditionally assessed by self-report despite its repeated demonstration of considerable inaccuracies. We argue here that it is time to move from the common view that self-reports of EI and PAEE are imperfect, but nevertheless deserving of use, to a view commensurate with the evidence that self-reports of EI and PAEE are so poor that they are wholly unacceptable for scientific research on EI and PAEE. While new strategies for objectively determining energy balance are in their infancy, it is unacceptable to use decidedly inaccurate instruments, which may misguide health care policies, future research, and clinical judgment. The scientific and medical communities should discontinue reliance on self-reported EI and PAEE. Researchers and sponsors should develop objective measures of energy balance.
Setting realistic weight loss goals may play a role in weight loss. We abstracted data from randomized controlled trials (RCTs) and observational studies conducted between 1998 and 2012 concerning the association of weight loss goals with weight loss. Studies included those that (i) were conducted in humans; (ii) delivered a weight loss intervention; (iii) lasted ≥6 weeks; (iv) assessed baseline weight loss goals; (vi) assessed pre and post weight either in the form of BMI or some other measure that could be converted to weight loss based on information included in the original study or later provided by the author(s); and (vii) assessed the correlation between weight loss goals and final weight loss or provided data to calculate the correlation. Studies that included interventions to modify weight loss goals were excluded. Eleven studies met inclusion criteria. The overall correlation between goal weight and weight at intervention completion was small and statistically insignificant (ρ^=0.05; p=0.20). The current evidence does not demonstrate that setting realistic goals leads to more favorable weight loss outcomes. Thus, our field may wish to reconsider the value of setting realistic goals in successful weight loss.
weight loss goals; obesity; overweight; desired weight loss outcomes
Researchers’ and participants’ expectations can influence
treatment response. Less is known about the effects of researchers’ expectations
on the accuracy of data collection in the context of a weight loss trial.
Student raters (N=58; age=20.1 ± 2.3 years) were recruited to weigh
individuals who they thought were completing a 12-month weight loss trial, although
these ‘participants’ were actually standardized patients (SPs) playing
these roles. Prior to data collection, student raters were provided information
suggesting that the tested treatment had been effective. Each student rater received a
list of 9-10 ‘participants’ to weigh. While the list identified each
person as ‘treatment’ or ‘control’, this assignment was at
random, which allowed us to examine the effects of non-blinding and expectancy
manipulation on weight measurement accuracy. We hypothesized that raters would record
the weights of ‘treatment participants’ as lower than those of
‘control participants’. This study is registered at ClinicalTrials.gov as COB12083.
Contrary to our hypothesis, raters recorded weights that were 0.293 kilograms
heavier when weighing ‘treatment’ versus ‘control’ SPs,
though this difference was not significant (p=0.175).
This pilot study found no evidence that manipulating expectancies about
treatment efficacy or not blinding raters biased measurements. Future work should
examine other bias which may be created by not blinding research staff who implement
weight loss trials as well as the participants in those trials.
weight; measurement; expectancy effect; randomized controlled trial; bias
Maternal genetic and phenotypic characteristics (e.g., metabolic and behavioral) affect both the intrauterine milieu and lifelong health trajectories of their fetuses. Yet at the same time, fetal genotype may affect processes that alter pre and postnatal maternal physiology, and the subsequent health of both fetus and mother. We refer to these latter effects as ‘fetal drive.’ If fetal genotype is driving physiologic, metabolic, and behavioral phenotypic changes in the mother, there is a possibility of differential effects with different fetal genomes inducing different long-term effects on both maternal and fetal health, mediated through intrauterine environment. This proposed mechanistic path remains largely unexamined and untested. In this study, we offer a statistical method to rigorously test this hypothesis and make causal inferences in humans by relying on the (conditional) randomization inherent in the process of meiosis. For illustration, we apply this method to a dataset from the Framingham Heart Study.
genetics; fetal effects; human; statistics; causal inference; intrauterine environment
Study-level design characteristics that inform the optimal design of obesity randomized controlled trials (RCTs) have been examined in few studies. A pre-randomization run-in period is one such design element that may influence weight loss. We examined 311 obesity RCTs published between January 1, 2007 and July 1, 2009 that examined weight loss or weight gain prevention as a primary or secondary endpoint. Variables included run-in period, pre-post intervention weight loss, study duration (time), intervention type, percent female, and degree of obesity. Linear regression was used to estimate weight loss as a function of 1) run-in (yes/no), and 2) run-in, time, percent female, body mass index, intervention type. Interaction terms were also examined. Approximately nineteen percent (18.6%) of the studies included a run-in period with pharmaceutical studies having the highest frequency. Although all intervention types were associated with weight loss (Mean = 2.80 kg, SD=3.52), the inclusion of a pre-randomization run-in was associated with less weight loss (p=0.0017) compared to studies that did not include a run-in period. However, this association was not consistent across intervention types. Our results imply that in trials primarily targeting weight loss in adults, run-in periods may not be beneficial for improving weight loss outcomes in interventions.
Randomized clinical trials; run-in periods; obesity
Background: Meta-research can involve manual retrieval and evaluation of research, which is resource intensive. Creation of high throughput methods (e.g., search heuristics, crowdsourcing) has improved feasibility of large meta-research questions, but possibly at the cost of accuracy.
Objective: To evaluate the use of double sampling combined with multiple imputation (DS + MI) to address meta-research questions, using as an example adherence of PubMed entries to two simple consolidated standards of reporting trials guidelines for titles and abstracts.
Methods: For the DS large sample, we retrieved all PubMed entries satisfying the filters: RCT, human, abstract available, and English language (n = 322, 107). For the DS subsample, we randomly sampled 500 entries from the large sample. The large sample was evaluated with a lower rigor, higher throughput (RLOTHI) method using search heuristics, while the subsample was evaluated using a higher rigor, lower throughput (RHITLO) human rating method. Multiple imputation of the missing-completely at-random RHITLO data for the large sample was informed by: RHITLO data from the subsample; RLOTHI data from the large sample; whether a study was an RCT; and country and year of publication.
Results: The RHITLO and RLOTHI methods in the subsample largely agreed (phi coefficients: title = 1.00, abstract = 0.92). Compliance with abstract and title criteria has increased over time, with non-US countries improving more rapidly. DS + MI logistic regression estimates were more precise than subsample estimates (e.g., 95% CI for change in title and abstract compliance by year: subsample RHITLO 1.050–1.174 vs. DS + MI 1.082–1.151). As evidence of improved accuracy, DS + MI coefficient estimates were closer to RHITLO than the large sample RLOTHI.
Conclusion: Our results support our hypothesis that DS + MI would result in improved precision and accuracy. This method is flexible and may provide a practical way to examine large corpora of literature.
double sampling; multiple imputation; CONSORT; meta-research; adherence; modeling
Whole Genome Prediction (WGP) jointly fits thousands of SNPs into a regression model to yield estimates for the contribution of markers to the overall variance of a particular trait, and for their associations with that trait. To date, WGP has offered only modest prediction accuracy, but in some cases even modest prediction accuracy may be useful. We provide an illustration of this using a theoretical simulation that used WGP to predict weight loss after bariatric surgery with moderate accuracy (R2 = 0.07) to assess the clinical utility of WGP despite these limitations. Prevention of Type 2 Diabetes (T2DM) post-surgery was considered the major outcome. Treating only patients above predefined threshold of predicted weight loss in our simulation, in the realistic context of finite resources for the surgery, significantly reduced lifetime risk of T2DM in the treatable population by selecting those most likely to succeed. Thus, our example illustrates how WGP may be clinically useful in some situations, and even with moderate accuracy, may provide a clear path for turning personalized medicine from theory to reality.
genomics; prediction; clinical application; methods; statistical genetics
CD8+ T cells are a key focus of vaccine development efforts for HIV. However, there is no clear consensus as to which of the nine HIV proteins should be used for vaccination. The early proteins Tat, Rev, and Nef may be better CD8+ T cell targets than the late-expressed structural proteins Gag, Pol, and Env. In this study, we show that Gag-specific CD8+ T cells recognize infected CD4+ T lymphocytes as early as 2 h postinfection, before proviral DNA integration, viral protein synthesis, and Nef-mediated MHC class I down-regulation. Additionally, the number of Gag epitopes recognized by CD8+ T cells was significantly associated with lower viremia (p = 0.0017) in SIV-infected rhesus macaques. These results suggest that HIV vaccines should focus CD8+ T cell responses on Gag.
The effect of weight loss on mortality rate is widely studied and of importance in the field of obesity. Separating the effects of intentional weight loss (IWL) from unintentional weight loss (UWL) has been a challenge. Most studies addressing this issue have used weight loss among people intending to lose weight as a surrogate of IWL. Coffey et al. (2005)  showed that these were not equivalent and developed a preliminary model to separate the effects of IWL from those of UWL. In this study we construct and implement Bayesian latent-variable linear models that allow the separation of the effects of IWL and UWL. The key idea of our method is to augment the unobserved UWL by using the information of observed weight loss among individuals not intending to lose weight. This data augmentation approach offers a way to estimate the effects of IWL and UWL as well as any parameters of interest. We applied our method to a real data set of rodent caloric restriction studies: our results suggest that IWL has a beneficial effect on mouse lifespan in contrast to UWL. Extensions to human data involving censored outcomes are discussed.
Bayesian analysis; Latent variables; Mortality; Obesity; Weight loss
The objective of this study was to examine the role of body mass and subcutaneous fat in injury severity and pattern sustained by overweight drivers. Finite element models were created to represent the geometry and properties of subcutaneous adipose tissue in the torso with data obtained from reconstructed magnetic resonance imaging datasets. The torso adipose tissue models were then integrated into the standard multibody dummy models together with increased inertial parameters and sizes of the limbs to represent overweight occupants. Frontal crash simulations were performed considering a variety of occupant restraint systems and regional body injuries were measured. The results revealed that differences in body mass and fat distribution have an impact on injury severity and pattern. Even though the torso adipose tissue of overweight subjects contributed to reduce abdominal injury, the momentum effect of a greater body mass of overweight subjects was more dominant over the cushion effect of the adipose tissue, increasing risk of other regional body injuries except abdomen. Through statistical analysis of the results, strong correlations (p < 0.01) were found between body mass index and regional body injuries except neck injury. The analysis also revealed that a greater momentum of overweight males leads to greater forward torso and pelvic excursions that account for higher risks (p < 0.001) of head, thorax, and lower extremity injury than observed in non-overweight males. The findings have important implications for improving the vehicle and occupant safety systems designed for the increasing global obese population.
Overweight; Crash injury; Modeling; Cushion effect; Momentum effect
The orexigenic hormone ghrelin, a potential antagonist of the insulin system, ensures sufficient serum glucose in times of fasting. In the race for new therapeutics for diabetes, one focus of study has been antagonizing the ghrelin system in order to improve glucose tolerance. We provide evidence for a differential role of a ghrelin agonist on glucose homeostasis in an Alzheimer’s disease mouse model fed a high–glycemic index diet as a constant challenge for glucose homeostasis. The ghrelin agonist impaired glucose tolerance immediately after administration but not in the long term. At the same time, the ghrelin agonist improved spatial learning in the mice, raised their activity levels, and reduced their body weight and fat mass. Immunoassay results showed a beneficial impact of long-term treatment on insulin signaling pathways in hippocampal tissue. The present results suggest that ghrelin might improve cognition in Alzheimer’s disease via a central nervous system mechanism involving insulin signaling.
To examine and compare the relationships among diet, physical activity, and adiposity between home-schooled children (HSC) and traditionally-schooled children (TSC).
Design and Methods
Subjects were HSC (n=47) and TSC (n=48) aged 7 to 12 years old. Dietary intakes were determined via two 24-hour recalls and physical activity was assessed with 7 days of accelerometry. Fat mass (FM), trunk fat, and percent body fat (%BF) were measured by dual-energy x-ray absorptiometry (DXA).
Relative to HSC, TSC demonstrated significantly higher BMI percentiles, FM, trunk fat, and %BF; consumed 120 total kilocalories more per day; and reported increased intakes of trans fats, total sugar, added sugars, calcium, and lower intakes of fiber, fruits, and vegetables (p<0.05). At lunch, TSC consumed significantly more calories, sugar, sodium, potassium, and calcium compared to HSC (p<0.05). Physical activity did not differ between groups. Traditional schooling was associated with increased consumption of trans fat, sugar, calcium (p<.05); lower intakes of fiber, and fruits and vegetables (p<.05); and higher FM, %BF, and trunk fat (p<0.01), after adjustment for covariates.
These data suggest HSC may consume diets that differ in energy and nutrient density relative to TSC, potentially contributing to differences in weight and adiposity.
obesity; adiposity; youth; nutrition; physical activity; diet quality
We provide arguments to the debate question and update a previous meta-analysis with recently published studies on effects of sugar-sweetened beverages (SSBs) on body weight/composition indices (BWIs). We abstracted data from randomized controlled trials examining effects of consumption of SSBs on BWIs. Six new studies met these criteria: 1) human trials, 2) 3 weeks duration, 3) random assignment to conditions differing only in consumption of SSBs, and 4) including a BWI outcome. Updated meta-analysis of a total of seven studies that added SSBs to persons’ diets showed dose-dependent increases in weight. Updated meta-analysis of eight studies attempting to reduce SSB consumption showed an equivocal effect on BWIs in all randomized subjects. When limited to subjects overweight at baseline, meta-analysis showed a significant effect of roughly 0.25 standard deviations (more weight loss/less weight gain) relative to controls. Evidence to date is equivocal in showing that decreasing SSB consumption will reduce the prevalence of obesity. Although new evidence suggests that an effect may yet be demonstrable in some populations, the integrated effect size estimate remains very small and of equivocal statistical significance. Problems in this research area and suggestions for future research are highlighted.
Randomized controlled trials; soda; beverages; soft drinks; obesity; weight loss; bias
To evaluate the association between body mass index (BMI: kg/m2) and mortality among Hispanic adults, we acquired 8 years (1997–2004) of National Health Interview Survey data linked to public-use mortality follow-up data through 2006. Using Cox proportional hazards regression, we fit separate models for two attained age strata (18 to <60 years, ≥60 years) adjusting for sex, smoking, and physical activity with over 38,000 analyzable respondents. We found that, among those aged ≥60 years, underweight (BMI ≤ 18.5) associated with elevated mortality (hazard ratio [HR] = 2.19; 95% confidence interval [CI], 1.38–3.46) while overweight (BMI of 25 to <30) and obesity grade 1 (BMI of 30 to <35) associated with reduced mortality (HR’s = 0.79; 95% CI, 0.65–0.95 and 0.71; 95% CI, 0.56–0.91), respectively. There were no significant associations between BMI and mortality among the 18 to <60 years attained age strata or among never smokers for either age strata. Overweight and obesity are not obviously associated with elevated mortality among Hispanic adults.
That one or multiple measures of metabolic rate may be robustly associated with, or possibly even causative of, the progression of aging-resultant phenotypes such as lifespan is a long-standing, well-known mechanistic hypothesis. To broach this hypothesis, we assessed metabolic function and spontaneous locomotion in two genetic and one dietary mouse models for retarded aging, and subjected the data to mediation analyses to determine whether any metabolic or locomotor trait could be identified as a mediator of the effect of any of the interventions on senescence. We do not test the hypothesis of causality (which would require some experiments), but instead test whether the correlation structure of certain variables is consistent with one possible pathway model in which a proposed mediating variable has a causal role. Results for metabolic measures, including oxygen consumption and respiratory quotient, failed to support this hypothesis; similar negative results were obtained for three behavioral motion metrics. Therefore, our mediation analyses did not find support that any of these correlates of decelerated senescence was a substantial mediator of the effect of either of these genetic alterations (with or without caloric restriction) on longevity. Further studies are needed to relate the examined phenotypic characteristics to mechanisms of aging and control of longevity.
physiology of longevity; gas-exchange (indirect calorimetry) metabolism; spontaneous physical activity; growth hormone hormonal signaling; caloric restriction; mediation analysis
The Medifast 5 & 1 Plan (MD) is a portion-controlled, nutritionally-balanced, low-fat weight-loss plan. We studied the effects of MD compared with a reduced-energy, food-based diet (FB) on body weight, waist circumference, fat mass, and other measures in adults.
We conducted a 2 parallel-arm, randomized, controlled trial comparing MD to FB over 52 weeks. A total of 120 men and women aged 19-65 years with BMI ≥35 and ≤50 kg/m2 were randomized to MD (n = 60) or FB (n = 60). Follow-up included a 26-week weight-loss phase and 26-week weight-maintenance phase. Anthropometric, body composition, biochemical, and appetite/satiety measures were performed at baseline, 26 and 52 weeks. An intention-to-treat, linear mixed models analysis was the primary analysis.
Fifty MD subjects (83.3%) and 45 FB subjects (75.0%) completed the study on assigned treatment. At 26 weeks, race-adjusted mean weight loss was 7.5 kg in MD subjects vs. 3.8 kg in FB subjects (P = 0.0002 for difference); reduction in waist circumference was 5.7 cm in MD vs. 3.7 cm in FB (P = 0.0064); and fat mass loss was 6.4 kg in MD vs. 3.7 kg in FB (P = 0.0011). At 52 weeks, the corresponding reductions were 4.7 vs. 1.9 kg (P = 0.0004); 5.0 vs. 3.6 cm (P = 0.0082); and 4.1 vs. 1.9 kg (P = 0.0019) in MD and FB subjects, respectively.
In obese adults, MD resulted in significantly greater reductions in body weight and fat compared with an FB diet for one year after randomization.
Meal replacements; obesity; weight-loss diets; weight maintenance
Childhood obesity remains a substantial health concern for our population and thoughtful attempts to develop and evaluate the utility of programs to reduce childhood obesity levels are needed. Unfortunately, we believe the conclusion by Burke et al. that the HealthMPowers program produces positive change in body composition is incorrect because the results obtained are likely due to regression to the mean (RTM), a well-known threat to the validity of studies that is often overlooked. Using empirical data, we demonstrate that RTM is likely to be the cause for the changes reported. A more reasonable conclusion than the one of effectiveness the authors offered would be that the results did not support the effectiveness of the intervention. Public health officials, parents, school leaders, community leaders, and regulators need and deserve valid evidence free from spin on which they can base decisions.
Four agents —acarbose (ACA), 17-α-estradiol (EST), nordihydroguaiaretic acid (NDGA) and methylene blue (MB) — were evaluated for lifespan effects in genetically heterogeneous mice tested at three sites. Acarbose increased male median lifespan by 22% (p< 0.0001),but increased female median lifespan by only 5% (p = 0.01). This sexual dimorphism in ACA lifespan effect could not be explained by differences in effects on weight. Maximum lifespan (90th percentile) increased 11% (p< 0.001) in males and 9% (p = 0.001) in females. EST increased male median lifespan by 12% (p = 0.002), but did not lead to a significant effect on maximum lifespan. The benefits of EST were much stronger at one test site than at the other two, and were not explained by effects on body weight. EST did not alter female lifespan. NDGA increased male median lifespan by 8 to 10% at three different doses, with p-values ranging from 0.04 to 0.005. Females did not show a lifespan benefit from NDGA, even at a dose that produced blood levels similar to those in males, which did show a strong lifespan benefit. MB did not alter median lifespan of males or females, but did produce a small, statistically significant (6%, p = 0.004) increase in female maximum lifespan. These results provide new pharmacological models for exploring processes that regulate the timing of aging and late-life diseases, and in particular for testing hypotheses about sexual dimorphism in aging and health.
lifespan; heterogeneous mice; acarbose; estradiol; NDGA; methylene blue
Introduction: Understanding participant demographic characteristics that inform the optimal design of obesity randomized controlled trials (RCTs) have been examined in few studies. The objective of this study was to investigate the association of individual participant characteristics and dropout rates (DORs) in obesity RCTs by pooling data from several publicly available datasets for analyses. We comprehensively characterize DORs and patterns in obesity RCTs at the individual study level, and describe how such rates and patterns vary as a function of individual level characteristics.
Methods: We obtained and analyzed nine publicly available, obesity RCT datasets that examined weight loss or weight gain prevention as a primary or secondary endpoint. Four risk factors for dropout were examined by Cox proportional hazards including sex, age, baseline BMI, and race/ethnicity. The individual study data were pooled in the final analyses with a random effect for study, and HR and 95% CIs were computed.
Results: Results of the multivariate analysis indicated that the risk of dropout was significantly higher for females compared to males (HR = 1.24, 95% CI = 1.05, 1.46). Hispanics and Non-Hispanic blacks had a significantly higher dropout rate compared to non-Hispanic whites (HR = 1.62, 95% CI = 1.37, 1.91; HR = 1.22, 95% CI = 1.11, 1.35, respectively). There was a significantly increased risk of dropout associated with advancing age (HR = 1.02, 95% CI = 1.01, 1.02) and increasing BMI (HR = 1.03, 95% CI = 1.03, 1.04).
Conclusion/Significance: As more studies may focus on special populations, researchers designing obesity RCTs may wish to oversample in certain demographic groups if attempting to match comparison groups based on generalized estimates of expected DORs, or otherwise adjust a priori power estimates. Understanding true reasons for dropout may require additional methods of data gathering not generally employed in obesity RCTs, e.g., time on treatment.
obesity; pooled analysis; randomized trials; dropout; participant characteristics