Katherine Mayhew Flegal

Katherine Mayhew Flegal
Stanford University | SU · Stanford Prevention Research Center

PhD

About

245
Publications
243,594
Reads
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157,585
Citations
Additional affiliations
August 2016 - present
Stanford University
Position
  • Consulting Professor
October 1987 - August 2016
Centers for Disease Control and Prevention
Position
  • Senior Researcher
December 1984 - July 1987
University of Michigan
Position
  • Research Investigator

Publications

Publications (245)
Article
After a long career at the National Center for Health Statistics, I retired and joined the Stanford Prevention Research Center as an unpaid associate. I was once described by a former US Food and Drug Administration commissioner as “one of the great epidemiologists.” The chair of the Harvard nutrition department, speaking on National Public Radio,...
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Objective: In 2019, Ward et al. proposed a method to adjust BMI calculated from self-reported weight and height for bias relative to measured data. They did not evaluate the adjusted values relative to measured BMI values for the same individuals. Methods: A large data set (n = 37,439) with both measured and self-reported weight and height was r...
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A naïve researcher published a scientific article in a respectable journal. She thought her article was straightforward and defensible. It used only publicly available data, and her findings were consistent with much of the literature on the topic. Her coauthors included two distinguished statisticians. To her surprise her publication was met with...
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Background: Several studies have assessed the relation of body composition to health outcomes by using values of fat and lean mass that were not measured but instead were predicted from anthropometric variables such as weight and height. Little research has been done on how substituting predicted values for measured covariates might affect analyti...
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Bland–Altman methods for assessing the agreement between two measures are highly cited. However, these methods may often not be used to assess agreement, and when used, they are not always presented or interpreted correctly. Our objective was to evaluate the use and the quality of reporting of Bland–Altman analyses in studies that compare self-repo...
Article
Objective: The aim of this study was to compare national estimates of self-reported and measured height and weight, BMI, and obesity prevalence among adults from US surveys. Methods: Self-reported height and weight data came from the National Health and Nutrition Examination Survey (NHANES), the National Health Interview Survey, and the Behavior...
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Guideline recommendations and health policy decisions rely on evidence from clinical and epidemiological studies. Adequate methodology and appropriate conclusions are essential to support healthcare and health policy decisions. An analysis of body mass index and mortality by the Global BMI Mortality Collaboration (GBMC) concluded that the associati...
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As the prevalence of obesity has increased over time in the United States (1,2), concern over the association between body weight and excess mortality also increased. In 2005, an analysis of estimated excess deaths, relative to the normal weight category (body mass index [BMI] 18.5-24.9), that were associated with underweight (BMI less than 18.5),...
Article
The term "obesity paradox" is a figure of speech, not a scientific term. The term has no precise definition and has been used to describe numerous observations that have little in common other than the finding of an association of obesity with a favorable outcome. The terminology has led to misunderstandings among researchers and the public alike....
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Misclassification of body mass index (BMI) categories arising from self-reported weight and height can bias hazard ratios in studies of BMI and mortality. We examined the effects on hazard ratios of such misclassification using national US survey data for 1976 through 2010 that had both measured and self-reported weight and height along with mortal...
Article
Background: A method applied in some large studies of weight and mortality is to begin with a well-defined analytic cohort and use successive restrictions in order to control for methodologic bias and arrive at final analytic results. Materials and methods: Two observational studies of body mass index and mortality allow a comparative assessment...
Article
Meta-analyses of individual participant data (MIPDs) offer many advantages and are considered the highest level of evidence. However, MIPDs can be seriously compromised when they are not solidly founded upon a systematic review. These data-intensive collaborative projects may be led by experts who already have deep knowledge of the literature in th...
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In Reply The intent of our comments was not to dismiss projection analyses but rather to point out that it may be difficult to extrapolate accurately from past data to future trends in obesity. Changes in obesity prevalence over time have not followed a readily predictable pattern. Projections can vary according to the starting time point chosen an...
Article
Importance Previous analyses of obesity trends among children and adolescents showed an increase between 1988-1994 and 1999-2000, but no change between 2003-2004 and 2011-2012, except for a significant decline among children aged 2 to 5 years. Objectives To provide estimates of obesity and extreme obesity prevalence for children and adolescents for...
Article
Importance Between 1980 and 2000, the prevalence of obesity increased significantly among adult men and women in the United States; further significant increases were observed through 2003-2004 for men but not women. Subsequent comparisons of data from 2003-2004 with data through 2011-2012 showed no significant increases for men or women. Objective...
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Analyses of the Third National Health and Nutrition Examination Survey (NHANES III) in 1988 to 1994 found an association of increasing blood lead levels <10 μg/dL with a higher risk of cardiovascular disease (CVD) mortality. The potential need to correct blood lead for hematocrit/hemoglobin and adjust for biomarkers for other metals, for example, c...
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Key findings: Obesity is associated with health risks (1,2). Monitoring the prevalence of obesity is relevant for public health programs that focus on reducing or preventing obesity. No significant changes were seen in either adult or childhood obesity prevalence in the United States between 2003-2004 and 2011-2012 (3). This report provides the mo...
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Obesity is a highly prevalent condition in the US and elsewhere and is associated with increased mortality and morbidity. Here we discuss some issues involved in quantifying the health burden of obesity using population attributable fraction (PAF) estimates and provide examples.Methods We searched PubMed for articles reporting attributable fraction...
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Studies of weight and mortality sometimes state that the mortality relative risks for obesity from nonsmokers are valid estimates of the relative risks for obesity in both smokers and nonsmokers. Extending this idea, several influential articles have used relative risks for obesity from nonsmokers and attributable fraction methods for unadjusted ri...
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The World Health Organization (Geneva, Switzerland) and the National Heart, Lung, and Blood Institute (Bethesda, Maryland) have developed standard categories of body mass index (BMI) (calculated as weight (kg)/height (m)(2)) of less than 18.5 (underweight), 18.5-24.9 (normal weight), 25.0-29.9 (overweight), and 30.0 or more (obesity). Nevertheless,...
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More than one-third of adults and 17% of youth in the United States are obese, although the prevalence remained stable between 2003-2004 and 2009-2010. To provide the most recent national estimates of childhood obesity, analyze trends in childhood obesity between 2003 and 2012, and provide detailed obesity trend analyses among adults. Weight and he...
Chapter
The prevalence of obesity among adults in the United States doubled between 1980 and 2000 and the prevalence remains high at over one third of the population. Obesity has been linked to increased morbidity and mortality in the USA and globally. In 2008, an estimated 502 million adults worldwide were obese. Obesity is estimated based on body mass in...
Chapter
Obesity results from an imbalance between energy intake and energy expenditure. Factors that influence energy intake include the quantity and quality of foods and beverages consumed, while physical activity levels influence energy expenditure. Energy balance is further influenced by genetic, metabolic, and environmental factors.
Chapter
Between 2010 and 2050, the American older adult population aged 65 years and older is projected to grow from 40.2 million to 88.5 million. Similar to estimates in the entire adult population, in 2007-2010 over a third of adults aged 65 years and older were obese, which represents over 13 million adults. Because both aging and obesity contribute to...
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Key findings: Data from the National Health and Nutrition Examination Survey, 2011-2012. More than one-third (34.9%) of adults were obese in 2011-2012. In 2011-2012, the prevalence of obesity was higher among middle-aged adults (39.5%) than among younger (30.3%) or older (35.4%) adults. The overall prevalence of obesity did not differ between men...
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In Reply: The goal of our study was neither to endorse nor to criticize the standard BMI categories developed by the World Health Organization, but rather to summarize the published findings on mortality from studies that used those widely recognized categories.As Dr Viña and colleagues point out, these are categories of weight and not body composi...
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Objectives: In 2000, the Centers for Disease Control and Prevention (CDC) released a new set of childhood growth charts for the United States. These charts included a set of smoothed percentiles along with LMS (lambda-mu-sigma) parameters to allow the calculation of other percentiles or standard deviation scores. These parameters resemble the LMS...
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Estimates of the relative mortality risks associated with normal weight, overweight, and obesity may help to inform decision making in the clinical setting. To perform a systematic review of reported hazard ratios (HRs) of all-cause mortality for overweight and obesity relative to normal weight in the general population. PubMed and EMBASE electroni...
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In the general population, obesity is associated with increased cardiovascular risk and decreased survival. In patients with end-stage renal disease (ESRD), however, an "obesity paradox" or "reverse epidemiology" (to include lipid and hypertension paradoxes) has been consistently reported, i.e. a higher body mass index (BMI) is paradoxically associ...
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Before estimating smoothed percentiles of weight-for-height and BMI-for-age to construct the WHO growth charts, WHO excluded observations that were considered to represent unhealthy weights for height. The objective was to estimate the effects of similar data trimming on empirical percentiles from the CDC growth-chart data set relative to the smoot...
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KEY FINDINGS: Data from the National Health and Nutrition Examination Survey, 2007-2010 More than one-third of older adults aged 65 and over were obese in 2007-2010. Obesity prevalence was higher among those aged 65‒74 compared with those aged 75 and over in both men and women. The prevalence of obesity in women aged 65-74 was higher than in women...
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In Reply: Drs Sauaia and Byers raise concerns about not including socioeconomic status in our analyses of trends in obesity using NHANES data. The objectives of these articles were to present the most recent national estimates of obesity prevalence and analyze trends between 1999-2000 and 2009-2010. Reducing disparities by race and ethnicity is a n...
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Between 1980 and 1999, the prevalence of adult obesity (body mass index [BMI] ≥30) increased in the United States and the distribution of BMI changed. More recent data suggested a slowing or leveling off of these trends. To estimate the prevalence of adult obesity from the 2009-2010 National Health and Nutrition Examination Survey (NHANES) and comp...
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The prevalence of childhood obesity increased in the 1980s and 1990s but there were no significant changes in prevalence between 1999-2000 and 2007-2008 in the United States. To present the most recent estimates of obesity prevalence in US children and adolescents for 2009-2010 and to investigate trends in obesity prevalence and body mass index (BM...
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The most recent national data on obesity prevalence among U.S. adults, adolescents, and children show that more than one-third of adults and almost 17% of children and adolescents were obese in 2009–2010. Differences in prevalence between men and women diminished between 1999–2000 and 2009–2010, with the prevalence of obesity among men reaching the...
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We sought to describe differences between normal weight, overweight, and obese adults in use of specific prescription medication classes. Cross-sectional analysis of prescription medication use among 9789 adults in the National Health and Nutrition Examination Survey, a nationally representative sample of the United States. In 2005-2008, 56.4% (95%...
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The high prevalence of obesity (defined by body mass index) among children and adolescents in the United States and elsewhere has prompted increased attention to body fat in childhood and adolescence. This report provides smoothed estimates of major percentiles of percentage body fat for boys and girls aged 8-19 years in the United States. Percenta...
Chapter
Published reports based on different definitions indicate that in Canada, Mexico and the United States childhood overweight and obesity have increased dramatically since 1980, with the US leading the way. The prevalence of overweight, using the International Obesity Task Force (IOTF) definitions (Cole et al. 2000) in 7–13 year old girls doubled in...
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BMI is one factor that is used to determine a child's eligibility for lipid screening and treatment. BMI, which is an indirect measure of body fat, may inadequately represent the biological effect of body fat percentage on lipid concentrations. We examined the relation between directly measured body fat percentage and lipid concentrations in a repr...
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Until quite recently, there has been a widespread belief in the popular media and scientific literature that the prevalence of childhood obesity is rapidly increasing. However, high quality evidence has emerged from several countries suggesting that the rise in the prevalence has slowed appreciably, or even plateaued. This review brings together su...
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Terminology and measures used in studies of weight and adiposity in children can be complex and confusing. Differences arise in metrics, terminology, reference values, and reference levels. Most studies depend on body mass index (BMI) calculated from weight and height, rather than on more direct measures of body fatness. Definitions of overweight a...
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In 1999, dual-energy x-ray absorptiometry (DXA) scans were added to the National Health and Nutrition Examination Survey (NHANES) to provide information on soft tissue composition and bone mineral content. However, in 1999-2004, DXA data were missing in whole or in part for about 21 per cent of the NHANES participants eligible for the DXA examinati...
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We used a first order discrete Markov model to investigate strategies to obtain unbiased estimates of the relative mortality hazard for comparing obese with non-obese participants. This hazard ratio is confounded by the fact that obese participants can be either sick or well, as can non-obese participants, and participants can migrate over time fro...
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In the United States, the prevalence of obesity among 2-19 year old children and adolescents tripled between 1980 and 1999. Between 1999 and 2008, however, the rate of increase slowed and the prevalence did not increase significantly. This chapter presents a review of published results on the obesity prevalence and trends between 1999-2000 and 2007...
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Data from the National Health and Nutrition Examination Survey, 2005-2008. Among men, obesity prevalence is generally similar at all income levels, however, among non-Hispanic black and Mexican-American men those with higher income are more likely to be obese than those with low income. Higher income women are less likely to be obese than low incom...
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Among non-Hispanic white children and adolescents, the prevalence of obesity increases as income decreases, yet the majority of non-Hispanic white children and adolescents who are obese do not live below 130% of the poverty level. In fact, overall, the majority of obese children do not live below 130% of the poverty level. All boys and girls and no...
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In studies of weight and mortality, the construct of reverse causation has come to be used to imply that the exposure-outcome relation is biased by weight loss due to preexisting illness. Observed weight-mortality associations are sometimes thought to result from this bias. Evidence for the occurrence of such bias is weak and inconsistent, suggesti...
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The prevalence of adult obesity has increased in recent decades. It is important to predict the long-term effect of body weight, and changes in body weight, in middle age on longevity and Medicare costs in older ages. The relationships between individuals' characteristics in middle age and subsequent Medicare costs and mortality were estimated from...
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A variety of different terms, metrics, and cut-off values have been used to describe and assess overweight and obesity in children. Body mass index (BMI) calculated as weight in kilograms divided by height in meters squared can be used to express weight adjusted for height. In order to account for variability by sex and age, BMI in children is comp...
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In Reply: In response to Dr Main and colleagues, we provide a Table that shows the age-standardized prevalence of grade 2 obesity (BMI of 35-<40), grade 3 obesity (BMI of ≥40), and grades 2 and 3 obesity (BMI of ≥35) among adults over the survey periods covered by our article. There were no statistically significant increases over the period 1999 t...
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This report presents body composition data from whole body dual energy x-ray absorptiometry scans for persons 8 years of age and older who participated in the National Health and Nutrition Examination Survey (NHANES) 1999-2004. Valid total body measurements were obtained on 16,973 individuals. Through the use of multiple imputation, a useable sampl...
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Estimates of obesity-associated deaths in the United States for 1991 were published by Allison et al (JAMA 1999;282:1530-8) and subsequently for 2000 by Mokdad et al (JAMA 2004;291:1238-45). Flegal et al (JAMA 2005;293:1861-7) then published lower estimates of obesity-associated deaths for 2000. All 3 studies incorporated data from the first Nation...
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Results from the National Health and Nutrition Examination Survey (NHANES) indicate that hypertension prevalence declined by 9% points from 34% in 1976-1980 to 25% in 1999-2002 in adults 20-74 years. The purpose of this study was to estimate the impact on hypertension prevalence of measurement error and selected risk factors. Using cross-sectional...
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This paper explores three issues related to the 2000 Centers for Disease Control and Prevention growth charts. First, it clarifies the methods that were used to create the charts as it has become apparent that the smoothing techniques have been somewhat misunderstood. The techniques included smoothing-selected percentiles between and including the...
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Body mass index (BMI)-for-age has been recommended as a screening test for excess adiposity in children and adolescents. We quantified the performance of standard categories of BMI-for-age relative to the population prevalence of high adiposity in children and adolescents overall and by race-ethnic group in a nationally representative US population...
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The prevalence of high body mass index (BMI) among children and adolescents in the United States appeared to plateau between 1999 and 2006. To provide the most recent estimates of high BMI among children and adolescents and high weight for recumbent length among infants and toddlers and to analyze trends in prevalence between 1999 and 2008. The Nat...
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The prevalence of obesity increased in the United States between 1976-1980 and 1988-1994 and again between 1988-1994 and 1999-2000. To examine trends in obesity from 1999 through 2008 and the current prevalence of obesity and overweight for 2007-2008. Analysis of height and weight measurements from 5555 adult men and women aged 20 years or older ob...
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Your article on female authorship as an indicator of gender imbalance in academic medicine in the UK is a welcome addition to the nucleus of data tracking women's progress. Change has been frustratingly slow. Although women's productivity and authorship have been a traditional means to track the status of women in these fields,1 women's roles as ed...