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Obesity and the Metabolic Syndrome

Authors: William T. Basco, Jr., MDFaculty and Disclosures



The PAS 2005 meeting had a plethora of presentations about obesity and the metabolic syndrome, both as invited science platform presentations and as original science abstracts presented as posters or platform presentations. This report covers a just a sampling of the obesity presentations, including a workshop reporting on the findings of a recent Institute of Medicine (IOM) report on childhood obesity, an invited science session on the metabolic syndrome, and selected original science abstracts reviewing the interactions of obesity and comorbid conditions.

Extent of the Obesity "Epidemic" and Recommendations to Address the Problem

One of the first events was the IOM-sponsored workshop on the extent of obesity in children and suggestions for prevention.[1] The session presenters included Thomas Robinson, Stanford University, Palo Alto, California; Dennis Bier, Baylor College of Medicine, Houston, Texas; and Vivica Kraak from IOM. This presentation was primarily an overview of the problem of obesity in the United States and a review of the suggested strategies for addressing this public health issue.

The IOM report, Preventing Childhood Obesity: Health in the Balance,[2] was released in September 2004 and is available for online preview and purchase. The executive summary of the document can also be viewed online.[3] The United States Congress requested this study be conducted in 2002; it was funded through a partnership of the Centers for Disease Control and Prevention (CDC), the National Institutes for Health, The Robert Wood Johnson Foundation and others. The task of the study was to develop a prevention-focused action plan to stem the rise in childhood obesity.

According to Dennis Bier,[1] who reviewed the epidemiology of obesity, over 9 million children age 6 and older are now considered obese. Since the 1970s, obesity has increased in all school age groups. The prevalence of obesity has doubled for children aged 2-5 years and for children aged 12-19 years. But even more significant is the fact that obesity has tripled in prevalence for those aged 6-11 years.

The IOM defines obesity as a body mass index (BMI) greater than the 95th percentile for age and gender.[2] In order to help clinicians identify these patients, the CDC produced BMI charts based on data from 1963 to 1994. It was determined that these older data should be used to try to capture the weights and heights of children before the clinical rise in obesity began in the late 1990s. A CDC primer on BMI and how to use growth charts is available in a CME/CE clinical update on Medscape.[4] BMI-for-age growth charts are also available online.[5]

There is a slight difference in the CDC and the IOM definitions for obesity. As mentioned previously, the IOM defines obesity as a BMI greater than 95th percentile for age and gender. The CDC would call those same children "overweight." The reason for this discrepancy is that the CDC reserves the term "obesity" for those children who are above the 95th percentile for age and gender but who are overweight due to excess body fat alone. The IOM classifies children as "obese" if they are above the 95th percentile, but admits that a small proportion of those are actually not in that percentile due to excess body fat alone.

Corresponding to the doubling of obesity rates, for 2- to 5-year-olds the current prevalence of obesity is 10%. For children aged 6-11 the prevalence is 15%, and for those aged 12-19 it is approximately 16%. All 3 of these age groups had an obesity prevalence of less than 5% from 1963-1970. Bier also emphasized that, according to data from Headley and colleagues,[6] the greatest rate of increase in prevalence was seen among minority individuals; approximately 25% of Mexican-American boys and 23% of black girls were classified as obese.

An "at risk" profile for obesity in childhood: individuals with parental obesity, low socioeconomic status, minorities, and individuals from the Southern region of the United States all appear to be at increased risk of becoming obese. However, it was noted that the root cause of the increased risk is unclear.

The biggest consequence of the obesity epidemic has been a large increase in the frequency and prevalence of type 2 diabetes mellitus (DM) in children. Children with type 2 DM now constitute an increasing proportion of patients in pediatric endocrinology clinics. There are many things that contribute to a child becoming obese, but the final common pathway is in an energy imbalance -- a difference between the calories taken in and the calories expended. Bier also emphasized that the current trends in obesity are almost certainly due to environmental rather than genetic factors. The time period from 1970 to 2005 is simply too short for genetic factors to produce such a large change in obesity prevalence. Genetic factors exert their effects over much longer time horizons.[1]

Vivica Kraak[1] reviewed some of the specifics of the IOM report. She emphasized that the full report provides a comprehensive review of the obesity prevention literature, and that any provider interested in determining what approaches to reducing overweight and obesity have been effective would find this report to be an invaluable resource. Key conclusions from the IOM report included:

  • Obesity is now a serious problem facing the United States.
  • Approaches to reduce obesity must revolve around the goal of establishing energy balance.
  • Societal changes at all levels are needed, and quickly, to address this issue.

The final point was most strongly emphasized in this presentation. Thomas Robinson reviewed the multilevel societal changes that will be needed to stem the obesity epidemic. The IOM committee, while preparing the report, struggled with the fact that rigorous evaluations of approaches to limit weight gain and encourage healthy lifestyles are sorely lacking from the existing obesity literature. Thus, the members felt that they were basing their recommendations on a dearth of published interventional studies. Such studies are emergently needed and absolutely essential to help guide policy.

Nevertheless, the IOM committee made the following suggestions for needed societal changes:

  1. Governmental involvement. Governmental agencies should provide clear guidance to corporations, communities, and individuals on healthy approaches to achieving energy balance.
  2. Marketplace and media. People in the United States need to be presented with healthier meals, and healthier eating must become a desired goal. Manufacturers should improve the labeling of products. For example, although a bag of potato chips may contain 3 servings, many individuals reading the label may not realize that they are reading the fat, sodium, and carbohydrate statistics for only 1 serving. Governmental agencies may need to institute new marketing guidelines. Finally, the media needs to clearly and forcefully incorporate healthy lifestyle messages into advertising.
  3. Communities. Multiple community agencies need to focus on the problem of obesity. Coalitions of groups will need to develop community-wide action plans to address the problem. Recommended changes include improving access to more healthy foods for low socioeconomic status individuals and improvements in the "built environment." In short, we all need to walk more and ride less.
  4. Schools. Schools need to get children to become more active. This may include increasing recess time, adding physical education back to school curricula, and redoubling the emphasis on health promotion classes. The committee suggested a goal of children having at least 30 minutes of cardiovascular activity per day as part of school curricula. The committee made a very strong statement that schools should get advertising, particularly for snack foods of all types, out of schools.
  5. Healthcare Providers. The authors in the report also have several recommendations for providers. These include:
    • Providers should routinely track BMI of their patients using the CDC charts.
    • When an individual is diagnosed as obese or at risk for becoming obese, the provider should provide relevant evidence-based counseling and guidance.
    • Providers should serve as role models, implementing or continuing their own healthy lifestyle, eating, and exercise habits.
    • Providers should provide community leadership and serve as a resource to communities. Many community-wide efforts will require the input of healthcare providers. In addition, providers can be a forceful voice in ensuring appropriate advertising, especially advertising in local schools.
  6. Health plans. Health plans should emphasize screening for obesity and pay for both screening and obesity-related interventions. This only seems to make sense given the exorbitant downstream costs of obesity related to cardiovascular problems and diabetes.
  7. Healthy homes. Although government and community efforts can be helpful, the home is the most influential environment for children. There is evidence that breastfeeding for 4-6 months exclusively can reduce the chance that a child will become obese.[7] In addition, greater emphasis should be placed on keeping healthful foods and healthful portions central in families' eating habits. The family should engage in regular physical activity. Families should also reduce "screen time" for children, including television and computers, to less than 2 hours per day. Finally, parents should be role models for their children in their own physical activities and eating habits, just as providers should be role models for their patients.
  8. Research. There is a pressing need for rigorous evaluation of potential interventions to reduce weight and improve healthy lifestyles in order to guide public policy. Behavioral intervention research is required to identify how to help individuals stick to the interventions determined to be effective. Additional community-based and population-based research on obesity is needed to help understand why certain ethnic groups and regions appear to be at increased risk for obesity.

Finally, the presenters described a resource that both clinicians and parents would find useful and user-friendly. It is a Web site created by the Children's Nutrition Research Center, a cooperative venture between Baylor College of Medicine Children's Hospital and the US Department of Agriculture/Agricultural Research Service.[8] This site has downloadable posters for parent education (eg, posters on serving sizes), brochures about weight management, news items, and nutrition calculators.

The Metabolic Syndrome

In addition to multiple presentations on the widespread prevalence of obesity, many presenters provided data about one of the most common results of obesity, the metabolic syndrome (MS). A Topic Symposium on metabolic syndrome was jointly sponsored by American Society of Pediatric Nephrology, the International Pediatric Hypertension Association, Lawson Wilkins Pediatric Endocrine Society, and PAS.

The first presentation, by Sonia Caprio,[9] Yale University, New Haven, Connecticut, began with a review of the current definition of metabolic syndrome, previously called "insulin resistance syndrome." In order to be classified as having metabolic syndrome, an individual should have 3 of the following conditions:

  1. Hypertension
  2. Altered glucose metabolism
  3. Dyslipidemia
  4. Obesity

Therefore, a person may be obese but not have full-blown MS. It is the full-blown MS that appears to have the greatest effect on increasing risk for cardiovascular disease.

Cook and colleagues[10] showed, in an analysis published in 2003, that the prevalence of MS in children was approximately 6% to 7%. Using data from the Third National Health and Nutrition Examination Survey (1988-1994), the investigators found that black males appeared to have a much lower rate of MS, and that there was a great deal of variation among ethnic groups and between genders. These data demonstrated that 28% of all obese children have MS. Data from de Ferranti and colleagues[11] published in 2004 demonstrated similar rates of MS in children, again finding that black children were less likely to have MS.

Although the definition of MS is better established in adults, there is also a building consensus for a definition in children. Cook's definition for MS included the following components:

  • waist circumference greater than 90th percentile for the age, gender, and ethnicity;
  • a fasting glucose of greater than 110 mg/dL;
  • blood pressure greater than 90th percentile for age and height;
  • Fasting triglycerides greater than 110 mg/dL; and
  • HDL cholesterol less than 40 mg/dL.

Even though other researchers have used slightly different variations of these components, it is notable that all investigations to date have found a fairly similar prevalence of MS.

The prevalence of MS appears to increase with increasing degrees of obesity. Weiss and colleagues[12] demonstrated that 30% of moderately obese children suffered from MS. The prevalence rose to 50% in children with severe obesity. There are 2 other notable findings of the Weiss study. First, these data demonstrated clearly that insulin resistance is perhaps the central problem in MS. Second, the study showed that children with obesity have an elevated baseline C-reactive protein (CRP) level.

Caprio concluded that the definition of MS still has room for evolution. For example, fasting glucose may be an inaccurate predictor of whether someone actually has impaired glucose tolerance. Patients may have a normal fasting glucose but have markedly abnormal and elevated 2-hour postprandial glucose. In addition, much more research needs to be conducted to determine whether insulin resistance is the critical component in producing the pathologic outcomes seen in patients with MS.

The structural vascular changes that occur in patients with MS were reviewed by Albert Rocchini,[13] University of Michigan, Ann Arbor. His central thesis was that obesity in children is associated with endothelial dysfunction, even in youth. There were several studies published in 2003, including research by Sorof and colleagues[14] demonstrating that obesity and hypertension in children are associated with vascular effects. In the Sorof study, children with obesity had a thickening of the intimal-media of the common carotid artery demonstrated on carotid artery ultrasound.

Although intimal-media thickness has not been directly linked to later cardiovascular disease, measuring it may prove to be a good noninvasive method for assessing future risk of atherosclerosis. The exact cause of intimal-media thickening is not known, but it may be related to the phenomenon of insulin resistance. The thickening leads to increased vascular resistance and contributes to elevated blood pressure levels. Rocchini's own study,[15] published in 1992, demonstrated that as obese children lose weight, their vascular resistance decreases along with decreasing insulin resistance. So while it seems clear that insulin resistance and vascular resistance are related, the direction of the association (which is the cause and which is the effect) remains undetermined.

There are other factors that may contribute to endothelial dysfunction in obesity, including changes in the renin-angiotensin-aldosterone system, the sympathetic nervous system, dyslipidemia, increased endothelin levels, and even chronic inflammation. In fact, future studies may look at whether blocking inflammatory pathways can help prevent the vascular outcomes that occur in MS.

Obesity and Asthma

In addition to invited science presentations about obesity and MS, other investigators presented original abstracts evaluating associations between obesity and asthma, another chronic medical condition often associated with obesity. Frintner and colleagues[16] presented an abstract sponsored by the American Academy of Pediatrics describing outcomes of a study that evaluated the degree of asthma symptoms among patients with increased BMI. Their findings were part of the Child Health Information Reporting Project, a 3-year study funded by the National Heart, Lung, and Blood Institute.

The data were obtained in urban and suburban Ohio; 414 children and their parents completed the study. The investigators asked the research question, "Do overweight children experience more asthma symptoms compared to normal weight peers?" They used CDC definitions, classifying children whose BMI for age was equal to the 95th percentile as overweight, children with a BMI between the 85th-95th percentile as at risk for overweight, and children whose BMI was less than the 85th percentile as normal weight. The parents in the sample completed questionnaires assessing the child's asthma symptoms and limitations of activity during the 2 previous weeks.

The sample included 406 children with a mean age of 11 years. The sample was 58% male, 45% black, 38% white and 11% Hispanic. Of the 406 children, 27% met the CDC definition for overweight; an additional 15% were at risk for overweight. Only 46% of the parents of overweight children reported that their child's health was "excellent/very good" compared with 50% of at-risk children and 70% of parents of children whose weight was normal. Overweight children were more likely to experience asthma symptoms, with 62% of them experiencing 1 or more asthma symptoms at least some of the time compared with only 48% of the normal-weight children. Thirty-two percent of the overweight children experienced limitations of strenuous activity compared with only 18% of the normal weight children.

The investigators concluded that overweight children and children at risk for overweight may experience more asthma symptoms and have greater limitations on their activities than children of normal weight. They contended that further efforts should help to delineate the exact relationship between overweight and asthma, and that asthma interventions may need to include weight reduction components for children who are overweight.

Susan Woolford and colleagues,[17] University of Michigan, evaluated the role of obesity in increasing the charges for patients experiencing inpatient asthma admissions. Their investigation analyzed information from the Agency for Healthcare Research and Quality's Kids Inpatient Database, which contains a nationally representative sample of pediatric hospital discharges from the year 2000. Length of stay and charges for children aged 1-18 years were included in the sample. Comparisons of the length of stay for asthma admissions for patients with obesity and without, as well as differences for pneumonia admissions for patients who were and were not obese, were made.

Children with asthma admissions complicated by obesity had a mean length of stay of 3.26 days compared with 2.32 days for children who were not obese (95% CI 2.97-3.54). In a similar fashion, obese children admitted for pneumonia stayed in the hospital 1 full day longer (at 4.4 days) than those who were not obese. Longer stays were associated with increased charges, with obese children admitted for asthma incurring an average of $8784.00 in charges compared with an average of only $5,724.00 in nonobese asthmatic patients. Similar excess costs were noted for obese children admitted for pneumonia. The investigators conclude that obesity in children with asthma is a problematic comorbid condition associated with increased hospitalization length and increased total charges.

Finally, findings from a study by Philomena Asante and colleagues[18] provided some guidance for providers regarding what parental behaviors targeting the obesity problem might be malleable with office-based counseling. This study, conducted by the Children's Hospital of Boston and the Center for Child Health Care Studies, Harvard Medical School, Massachusetts, included 300 parents of children aged 3-13 years. The children presented to a single clinic during 2004.

The investigators evaluated parental willingness to institute behavioral and nutritional changes that would help children who are overweight. These changes included: decreasing meal portion sizes, exercising as a family, watching less TV, eating less fast food, drinking less soda, eating more vegetables, eating together as a family, and eating more fruits. Parents were able to respond that they either planned to implement the change, might implement the change, or that they did not plan to implement the change. The sample was 54% black and 20% Hispanic.

The proactive behaviors that were best accepted by parents were drinking less soda, eating more vegetables and fruits, and eating more together as a family. Of particular note: 93% of the parents of overweight children agreed to drinking less soda. The lowest planned implementation rates (at 58% and 71%, respectively) were for decreasing meal portion sizes and for exercising as a family. Parents of normal-weight children drove the relatively low acceptance of these 2 changes. When looking at responses by parents of only the overweight children, 77% of those same parents agreed to decrease meal portion sizes. The investigators concluded that parents are in need of counseling on healthier lifestyle choices, but cautioned that parental readiness to change is low in areas that might be most beneficial such as decreasing meal sizes and increasing physical activity.

Reviewer comment:

Obesity, and its downstream effects such as hypertension and other components of MS, will be a central part of pediatric practice for many years to come. We will all need to accept the problem as a significant one; learn the components of MS, how to screen for them and the abnormal "cutoff" values; and how to find local resources and perhaps establish within-practice resources to help obese patients.


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