Biomedical subjects

D B Allison

Publications and source records attributed to D B Allison.

At least 19 recordsLinked to original sources

PubMed1999

Estimated intakes of trans fatty and other fatty acids in the US population.

OBJECTIVE: To estimate mean level of trans fatty acid intakes using a representative sample of the US population. DESIGN: The study used food intake data from the 1989-1991 Continuing Survey of Food Intakes by Individuals (CSFII) and the trans fatty acid contents of specific foods calculated from a database compiled by the US Department of Agriculture (USDA) to estimate the mean level and deciles of trans fatty acid intake of the representative US population. SUBJECTS/SETTING: Trans fatty acid intakes were estimated for each subject (N = 11,258) in the CSFII data who completed both a 24-hour recall and a 2-day food record. STATISTICAL ANALYSES PERFORMED: Weights developed by USDA for the survey were used for all data analyses. The Technical Assessment Systems (TAS) International Diet Research System (TAS-DIET), software developed by TAS, was used to derive weighted estimates of the mean and percentiles of the intake distribution. PC CARP, software designed by Iowa State University, was used to estimate standard errors. RESULTS: Mean percentage of energy ingested as trans fatty acids was 2.6% and the mean percentage of total fat ingested as trans fatty acids was 7.4%. Across all age and gender groups examined, estimates ranged from 2.6% to 2.8% and 7.1% to 7.9%, respectively. APPLICATIONS/CONCLUSIONS: Dietetics practitioners can use the representative data of this study to help clients achieve desired changes in consumption levels of trans fatty acids.

Adolescent↗

PubMed1998

Garcinia cambogia (hydroxycitric acid) as a potential antiobesity agent: a randomized controlled trial.

CONTEXT: Hydroxycitric acid, the active ingredient in the herbal compound Garcinia cambogia, competitively inhibits the extramitochondrial enzyme adenosine triphosphate-citrate (pro-3S)-lyase. As a citrate cleavage enzyme that may play an essential role in de novo lipogenesis inhibition, G cambogia is claimed to lower body weight and reduce fat mass in humans. OBJECTIVE: To evaluate the efficacy of G cambogia for body weight and fat mass loss in overweight human subjects. DESIGN: Twelve-week randomized, double-blind, placebo-controlled trial. SETTING: Outpatient weight control research unit. PARTICIPANTS: Overweight men and women subjects (mean body mass index [weight in kilograms divided by the square of height in meters], approximately 32 kg/m2). INTERVENTION: Subjects were randomized to receive either active herbal compound (1500 mg of hydroxycitric acid per day) or placebo, and both groups were prescribed a high-fiber, low-energy diet. The treatment period was 12 weeks. Body weight was evaluated every other week and fat mass was measured at weeks 0 and 12. MAIN OUTCOME MEASURES: Body weight change and fat mass change. RESULTS: A total of 135 subjects were randomized to either active hydroxycitric acid (n = 66) or placebo (n = 69); 42 (64%) in the active hydroxycitric acid group and 42 (61%) in the placebo group completed 12 weeks of treatment (P = .74). Patients in both groups lost a significant amount of weight during the 12-week treatment period (P<.001); however, between-group weight loss differences were not statistically significant (mean [SD], 3.2 [3.3] kg vs 4.1 [3.9] kg; P = .14). There were no significant differences in estimated percentage of body fat mass loss between treatment groups, and the fraction of subject weight loss as fat was not influenced by treatment group. CONCLUSIONS: Garcinia cambogia failed to produce significant weight loss and fat mass loss beyond that observed with placebo.

Adult↗

PubMed1998

The search for human obesity genes.

Understanding of the genetic influences on obesity has increased at a tremendous rate in recent years. By some estimates, 40 to 70 percent of the variation in obesity-related phenotypes in humans is heritable. Although several single-gene mutations have been shown to cause obesity in animal models, the situation in humans is considerably more complex. The most common forms of human obesity arise from the interactions of multiple genes, environmental factors, and behavior, and this complex etiology makes the search for obesity genes especially challenging. This article discusses the strategies currently being used to search for human obesity genes and recent promising results from these efforts.

Animals↗

PubMed1998

Power and sample size for survival analysis under the Weibull distribution when the whole lifespan is of interest.

Accessible and readily utilized software, tables and approximation formulae have been developed to estimate power and sample size for studies of time to event (survival times) when the survival times are assumed to be exponential. These methods can markedly misestimate power when the distribution is Weibull and not exponential. The Weibull distribution with increasing hazard is common in aging research, especially when the whole life span of the subjects is of interest. This note considers an extension of power and sample size calculations, previously developed under the exponential distributional assumption, to the more general case of the Weibull distribution for a prospective comparative follow-up study. The hypotheses are defined in terms of the ratio of the median survival times between two groups. It is shown that the power and sample sizes are heavily dependent on the shape parameter of the Weibull distribution. Using the extensions developed, investigators can use existing software and tables to calculate power and sample size under the assumption of a Weibull distribution.

Algorithms↗

PubMed1998

Do unsuccessful dieters intentionally underreport food intake?

OBJECTIVE: A bogus pipeline paradigm was utilized to assess whether food intake underreporting by unsuccessful dieters is intentional. METHOD: Twenty-eight subjects completed 1-week food diaries. Then, 17 subjects in the experimental condition kept 2-week food diaries while being told the researcher was verifying their report. Eleven subjects in the control group were asked merely to self-monitor for two more weeks. RESULTS: Results indicate that subjects in the experimental group reported significantly greater intake than control subjects, when controlling for reported intake during the screening phase and weight change. DISCUSSION: Thus, the belief that the researcher could verify their report improved the accuracy of patients' self-report. However, all subjects continued to underreport their dietary intake. In summary, underreporting may be an intentional attempt to manage presentation to others in a society that is increasingly critical of overweight persons.

Adult↗

PubMed1998

Measurement challenges and other practical concerns when studying massively obese individuals.

OBJECTIVE: To describe the measurement challenges faced and to evaluate the measurement quality obtained with massively obese individuals. METHOD: A cross-sectional analysis of 107 individuals with body mass indices (kg/m2) > or = 50 was conducted. Individuals had their body fat measured via bioimpedance analysis (BIA), their serum leptin levels measured via radioimmunoassay (RIA), and height and weight measured via both laboratory scales and self-report. RESULTS: Serum leptin appeared to be measured accurately, provided the serum was diluted prior to conducting the RIA. Difficulties remained, however, in evaluating what was an unusual or expected value of leptin among individuals this large. Measures of impedance appeared to provide reasonable ordinal indications of body fatness. However, currently available equations for converting measures of impedance to estimates of percent body fat were highly inaccurate. Self-reported height and weight were reasonably good proxies of measured height and weight among individuals who reported their height and weight. However, a substantial proportion were unable to provide estimates. DISCUSSION: The above results suggest there are substantial challenges when trying to obtain meaningful measurements regarding obesity-related variables among massively obese individuals. Other logistic challenges also are discussed. It is hoped future research is directed at overcoming some of these challenges.

Adipose Tissue↗

PubMed1998

Method and computer program for controlling the family-wise alpha rate in gene association studies involving multiple phenotypes.

Multiple significance testing involving multiple phenotypes is not uncommon in the context of gene association studies but has remained largely unaddressed. If no adjustment is made for the multiple tests conducted, the type I error probability will exceed the nominal (per test) alpha level. Nevertheless, many investigators do not implement such adjustments. This may, in part, be because most available methods for adjusting the alpha rate either: 1) do not take the correlation structure among the variables into account and, therefore, tend to be overly stringent; or 2) do not allow statements to be made about specific variables but only about multivariate composites of variables. In this paper we develop a simulation-based method and computer program that holds the actual alpha rate to the nominal alpha rate but takes the correlation structure into account. We show that this method is more powerful than several common alternative approaches and that this power advantage increases as the number of variables and their intercorrelations increase. The method appears robust to marked non-normality and variance heterogeneity even with unequal numbers of subjects in each group. The fact that gene association studies with biallelic loci will have (at most) three groups (i.e., AA, Aa, aa) implies by the closure principle that, after detection of a significant result for a specific variable, pairwise comparisons for that variable can be conducted without further adjustment of the alpha level.

Analysis of Variance↗

PubMed1998

Demand characteristics of the research setting can influence indexes of negative affect-induced eating in obese individuals.

Measures of negative affect-induced eating (NAIE) are common in clinical research with obese individuals. However, previous studies suggest that measures of NAIE can be induced by social desirability tendencies or demand characteristics of the research setting. Using an experimental design, the present study tested the effects of demand characteristics of the research setting on self-report and behavioral indexes of NAIE. Obese and nonobese subjects (n=107) were randomly assigned to an experimental or control group. Experimental subjects received a lecture indicating an association between emotional eating and obesity; control subjects received no information. Outcome measures were indexes of NAIE from a questionnaire, food diaries, and food intake during a laboratory "taste test." We hypothesized that the association between relative body mass and NAIE would be stronger among subjects receiving the lecture manipulation than control subjects. Results indicated that NAIE indexes, particularly from food diaries, were influenced modestly by research demand characteristics. We conclude that demand characteristics of the research setting can affect indexes of NAIE among obese persons.

Adolescent↗

PubMed1998

Prader-Willi syndrome: relationship of adiposity to plasma leptin levels.

OBJECTIVE: Prader-Willi syndrome (PWS) is an autosomal dominant disorder involving the proximal long arm of chromosome 15, in which obesity is common. However, there is limited information on the underlying physiological mechanisms promoting obesity in this population. We tested whether there was a significant positive association between leptin and total body fat (TBF) in subjects with PWS, and whether this association was stronger among subjects with than without PWS. RESEARCH METHODS AND PROCEDURES: We studied 21 PWS patients and 64 non-PWS controls on whom we measured serum leptin, total body fat, glucose, insulin, and resting energy expenditure. We tested whether the slope of the regression line between leptin and TBF (in kg), measured by dual energy X-ray absorptiometry, was the same for PWS patients and non-PWS controls. RESULTS: Regression analyses indicated that the leptin-TBF association was significantly stronger among PWS patients. In contrast, the slope of the leptin-body mass index association did not significantly differ between PWS patients and non-PWS controls. None of the other outcome variables showed associations with leptin. DISCUSSION: Results suggest that the role of leptin in promoting obesity may be greater among subjects with PWS than among non-PWS controls.

Absorptiometry, Photon↗

PubMed1998

Relative body weight and self-esteem among African Americans in four nationally representative samples.

OBJECTIVE: Obesity is an increasingly common health problem among African Americans, especially women, in the United States. However, limited data are available on the psychological correlates of obesity in this population. This study examined the association between self-esteem and relative body weight (RBW) in four large nationally representative samples of African American individuals. RESEARCH METHODS AND PROCEDURES: Data from The Adolescent Health Care Evaluation Study, The National Longitudinal Survey of Youth, The High School and Beyond, and The National Survey of Black Americans were analyzed. Within each database, regression analyses tested the association between RBW and self-esteem while adjusting for age and sex. RESULTS: In three of the four databases, there was no significant association between RBW and self-esteem. In the only database detecting a statistically significant effect, the magnitude of the effect was small. The combined effects of RBW and its interaction with age and sex accounted for <2% of the variance in self-esteem across databases. DISCUSSION: Results suggest that elevated RBW is not associated with a poorer general self-concept, on average, among African American individuals.

Adolescent↗

PubMed1998

Body mass index as a measure of adiposity among children and adolescents: a validation study.

OBJECTIVES: To test the hypothesis that in a healthy pediatric population body mass index (BMI) (kilograms per meter square) is a valid measure of fatness that is independent of age for both sexes. METHODS: Total body fat (TBF) (in kilograms) and percent of body weight as fat (PBF) were estimated by dual energy x-ray absorptiometry (DXA) in 198 healthy Italian children and adolescents between 5 and 19 years of age. We developed multiple regression analysis models with TBF and percent body fat as dependent variables and BMI, age, and interaction terms as independent variables. Separate analyses were conducted for boys and girls. RESULTS: BMI was strongly associated with TBF (R2 = 0.85 and 0.89 for boys and girls, respectively) and PBF (R2 =0.63 and 0.69 for boys and girls, respectively). Confidence limits on BMI-fatness association were wide, with individuals of similar BMI showing large differences in TBF and in PBF. Age was a significant covariate in all regression models. Addition of nonlinear terms for BMI did not substantially increase the R2 for TBF and PBF models in boys and girls. CONCLUSION: Our results support the use of BMI as a fatness measure in groups of children and adolescents, although interpretation should be cautious when comparing BMI across groups that differ in age or when predicting a specific individual's TBF or PBF.

Absorptiometry, Photon↗

PubMed1998

Meta-analysis of the association of the Trp64Arg polymorphism in the beta3 adrenergic receptor with body mass index.

OBJECTIVE: As a result of efforts to isolate obesity-promoting genes, the Trp64Arg polymorphism in the beta3 adrenergic receptor locus, has been studied by many investigators. Results of the studies have varied in statistical significance and magnitude of the association of the polymorphism with body mass index (BMI: kg/m2). This has led to controversy about whether this polymorphism is associated with meaningful changes in BMI. To clarify the possible association, we conducted a meta-analysis. DESIGN: Meta-analytic study. MEASUREMENTS: For each genotype of the beta3 adrenergic receptor (Trp/Trp; Trp/Arg; Arg/Arg), we extracted the number of subjects, mean and standard deviation of BMI from 23 studies, including 36 different subgroups with a total of 7399 subjects. Other indices and obesity-related variables were not considered. RESULTS: No significant association of the Trp64Arg polymorphism with BMI was found. The weighted mean BMI difference between Trp/Trp homozygotes and Trp/Arg heterozygotes was 0.19 (s.e. = 0.11; P = 0.07). In addition, the distribution of effect sizes was not significantly heterogeneous (chi2=38.68; df 35; P = 0.31) suggesting that the variation of the effect sizes across the subgroups is not significant. A further weighted regression analysis, utilizing all three genotypes and adjusting for the random subgroup effect, also showed the effect of the polymorphism on BMI is not significant (F = 1.72, df = (2,54), P = 0.19). CONCLUSION: Based on existing data, the Trp64Arg polymorphism does not appear to be significantly associated with BMI. Moreover, we found no evidence for effect heterogeneity, suggesting that the effect of the polymorphism is not moderated by ethnicity or diabetic status.

Arginine↗

PubMed1998

Multiple phenotype modeling in gene-mapping studies of quantitative traits: power advantages.

Genomewide searches for loci influencing complex human traits and diseases such as diabetes, hypertension, and obesity are often plagued by low power and interpretive difficulties. Attempts to remedy these difficulties have typically relied on, and have promoted the use of, novel subject-ascertainment schemes, larger sample sizes, a greater density of DNA markers, and more-sophisticated statistical modeling and analysis strategies. Many of these remedies can be costly to implement. We investigate the utility of a simple statistical model for the mapping of quantitative-trait loci that incorporates multiple phenotypic or diagnostic endpoints into a gene-mapping analysis. The approach considers finding a linear combination of multiple phenotypic values that maximizes the evidence for linkage to a locus. Our results suggest that substantial increases in the power to map loci can be obtained with the proposed technique, although the increase in power obtained is a function of the size and direction of the residual correlation among the phenotypes used in the analysis. Extensive simulation studies are described that justify these claims, for cases in which two phenotypic measures are analyzed. This approach can be easily extended to cover more-complex situations and may provide a basis for more insightful genetic-analysis paradigms.

Chromosome Mapping↗

PubMed1998

Estimating African American admixture proportions by use of population-specific alleles.

We analyzed the European genetic contribution to 10 populations of African descent in the United States (Maywood, Illinois; Detroit; New York; Philadelphia; Pittsburgh; Baltimore; Charleston, South Carolina; New Orleans; and Houston) and in Jamaica, using nine autosomal DNA markers. These markers either are population-specific or show frequency differences >45% between the parental populations and are thus especially informative for admixture. European genetic ancestry ranged from 6.8% (Jamaica) to 22.5% (New Orleans). The unique utility of these markers is reflected in the low variance associated with these admixture estimates (SEM 1.3%-2.7%). We also estimated the male and female European contribution to African Americans, on the basis of informative mtDNA (haplogroups H and L) and Y Alu polymorphic markers. Results indicate a sex-biased gene flow from Europeans, the male contribution being substantially greater than the female contribution. mtDNA haplogroups analysis shows no evidence of a significant maternal Amerindian contribution to any of the 10 populations. We detected significant nonrandom association between two markers located 22 cM apart (FY-null and AT3), most likely due to admixture linkage disequilibrium created in the interbreeding of the two parental populations. The strength of this association and the substantial genetic distance between FY and AT3 emphasize the importance of admixed populations as a useful resource for mapping traits with different prevalence in two parental populations.

Africa↗

PubMed1998

Body mass index, smoking, and mortality among older American women.

The relationship among body mass index (BMI, kg/m2), smoking status, and overall mortality remains controversial. To assess this relationship in a representative sample of older women, we used data from the Panel Study of Income Dynamics (PSID). The PSID (begun in 1968) is a prospective longitudinal cohort study designed to examine economic and demographic behavior. Respondents were 1355 women age > or = 50 when they initially completed the Self-Administered Health Questionnaire in 1990. Data collected included self-reported height and weight, years of completed education, smoking status (never versus ever), and responses to four health-related questions (e.g., retired due to ill health, difficulty eating). Respondents were followed, including the date of death if respondent died, through 1994. Cox proportional hazard regression revealed a U-shaped relationship irrespective of whether smoking was included in the model. The base of the curve was fairly wide, suggesting that a broad range of BMI is well tolerated by older women. The minimum mortality (estimated from fitted proportional hazard models) for both the smoking and nonsmoking models occurred at a BMI of approximately 34. When interactions between smoking status and BMI terms were added to the model, the interactions were not jointly significant (p = 0.071). Moreover an exploratory plot of the BMI-mortality curve among never smokers (n = 800) revealed a curve that moved away from being U-shaped toward being more monotonically decreasing. It is concluded that these data suggest that there is no evidence that the U-shaped BMI-mortality relationship observed is caused by confounding by smoking status.

Aged↗

PubMed1998

Meta-analysis of linkage data under worst-case conditions: a demonstration using the human OB region.

To date, few methods have been developed explicitly for meta-analysis of linkage analyses. Moreover, the methods that have been developed or suggested generally depend on certain ideal situations and have not been widely applied. In this article, we apply standard statistical theory and meta-analytic techniques in novel ways to five published papers discussing the evidence of linkage of body mass index (BMI) to the region of the human genome containing the OB gene. These methods are "inference based," meaning that they allow one to make statements about the statistical significance of the entire body of evidence. As currently developed, they do not allow specific statements to be made about the amount of variance explained by any putative locus or allow precise confidence intervals to be placed around the putative location of a linked locus. By applying these techniques to the literature on linkage in the human OB gene region, we are able to show that the evidence for linkage somewhere in the region is extremely strong (P = 1.5 x 10[-5]).

Body Mass Index↗

PubMed1997

Examination of "early mortality exclusion" as an approach to control for confounding by occult disease in epidemiologic studies of mortality risk factors.

Methods for the estimation of the effects of chronic disease risk factors on mortality continue to be an area that generates confusion and controversy. In response to the frequently observed U- or J-shaped relations between risk factors and mortality, some authors suggest that subjects dying during the first k years of follow-up (where k is some positive number less than the total length of follow-up) be excluded from statistical analyses. By excluded, the authors mean completely removed from the data set. The rationale is that persons dying during the first k years are likely to have a preexisting occult disease that confounds the relation between the risk factor under study and mortality. Excluding persons dying during the first k years of follow-up purportedly reduces this confounding. However, the authors are aware of no demonstration that this procedure effectively accomplishes its goal. They show that excluding subjects who die during the first k years of follow-up does not necessarily lead to a reduction in bias in the estimated effect of a risk factor on mortality when this relation is confounded by the presence of occult disease. Moreover, it is possible for such exclusion to exacerbate the confounding due to preexisting disease. Thus, excluding subjects dying during the first k years of follow-up is not necessarily an effective strategy for dealing with confounding due to occult disease. Investigators are encouraged to pursue alternative methods.

Confounding Factors, Epidemiologic↗

PubMed1997

Hypothesis concerning the U-shaped relation between body mass index and mortality.

Numerous studies have documented a U- or J-shaped association between body mass index (BMI) (kg/m2) and mortality, such that increased mortality rate is associated with relatively low and high BMI values. It has been argued elsewhere that the elevated mortality rate observed at lower BMI values actually results from the effects of unmeasured confounding variables, in particular smoking status and preexisting disease. In this paper, the authors present an additional explanation for the phenomenon, i.e., nonspecific measurement. They propose that differential health consequences of fat mass and fat-free mass can be masked by the use of BMI when studied in relation to mortality. To illustrate this point, they use body composition data from 1,137 healthy adults and specify a hypothetical underlying BMI-mortality model in which the logit of death increased linearly with fat mass and decreased linearly with fat-free mass, and % fat increased monotonically with BMI. The results indicate that, even under these specifications, the authors can recover a U-shaped association between BMI and mortality. Consistent with previous suggestions in the literature, future epidemiologic studies that examine the association between adiposity and mortality should prioritize the use of body composition measures.

Adolescent↗