Obesity as a metabolic syndrome determinant and the influence of physical activity in treatment and prevention

Abstract

The prevalence of obesity in both the developed and developing world have increased, which leads to diverse health outcomes and is placing a heavy burden on the economy. Abdominal obesity proved to be one of the main features in predicting metabolic and cardiovascular disease (CVD) risk and may be the link that unifies the metabolic syndrome (MS) through pro-inflammatory pathways. While the pathogenesis of the MS and each of its components are complex and not well understood, abdominal obesity remains the mechanism that relates to increased lipolysis causing the liver to increase blood glucose and very low lipoprotein output. This in turns leads to raised blood glucose, triglycerides, low-density lipoprotein cholesterol (LDL-C), blood pressure and inflammatory markers (C-reactive protein, interleukin-6 and tumor necrosis factor-a) and decreased high-density lipoprotein cholesterol (HDL-C). Prevention of the metabolic syndrome and treatment of its main characteristics are now considered of utmost importance in order to combat the increased CVD risk and all-cause mortality. Decreasing sedentary behaviour through regular physical activity is a key element in successful treatment of obesity through an increase in energy expenditure, but the ability to decrease low-grade systemic inflammation may be an even greater outcome. Aims The aims of this study was firstly, to determine by means of a literature review, how obesity could be related to a state of chronic systemic inflammation (increased CRP and IL-6). Secondly to determine whether physical activity could serve as a suitable method to decrease inflammation associated with obesity and related disorders. Thirdly to determine if abdominal obesity is a predictor of the metabolic syndrome and CVD and finally, to determine if measures of obesity can predict risk for the metabolic syndrome and CVD risk. Methods For this review study, a computer-assisted literature search were utilized to identify research published between 1990 and 2005. the following databases were utilized for the search: NEXUS, Science Direct, PubMed and Medline. Keywords related to obesity (abdominal obesity, overweight), metabolic syndrome (insulin resistance syndrome, dysmetabolic syndrome, syndrome X), cardiovascular disease (coronary heart disease, coronary artery disease), cardiovascular risk factors (hypertension, dyslipidemia, diabetes mellitus, physical activity), inflammatory markers (CRP, IL-6, chronic low-grade inflammation) and physical activity (fitness, exercise and training) were included as part of the search, including the references identified by previous reviewers (not identified as part of the computerized literature search). Results and conclusions Several research studies concluded that obesity could be an inflammatory disorder due to low-grade systemic inflammation. Adipose tissue is known to be a sectretory organ producing cytokines, acute phase reactants and other circulating factors. The synthesis of adipose tissue TNF-a could induce the production of IL-6, CRP and other acute phase reactants. CRP is a acute phase reactant, synthesized primarily in hepatocytes and secreted by the liver in response to a variety of inflammatory cytokines of which IL-6 and TNF-a are mainly involved. CRP increases rapidly in response to trauma, inflammation and infection. Thus, enhanced levels of CRP can be used as a marker of inflammation. Several studies of large population cohorts provide evidence for an inverse, independent dose-response relation between plasma CRP concentration and level of physical activity in both men and women. Trends for decreased IL-6, TNF-a and CRP concentrations were linear with increasing amounts of reported exercise in most of the research studies, physical activity proved effective in lowering measures of adiposity (BMI, WHR, WC and percentage body fat) and obesity related inflammatory markers (CRP & IL-6). Thereby indicating a potential anti-inflammatory effect. In the studies reviewed in this article abdominal obesity is identified as a predictor and independent risk factor for CVD in both men and women. High levels of deep abdominal fat have also been correlated with components of the metabolic syndrome, glucose intolerance, hyperinsulinemia, hypertension, diabetes, increases in plasma triglyceride levels and a decrease in HDL-C levels (dyslipidemia) in many of the studies. Prospective epidemiological studies have revealed that abdominal obesity (determined by WC and WHR) conveys an independent prediction of CVD risk and is more relevant compared to general obesity (determined by BMI). Abdominal fat has been linked to metabolic risk factors like high systolic blood pressure, atherogenic dyslipidemia, with increased serum TG and decreased HDL-C, and glucose intolerance. Although magnetic resonance imaging (MRI) and computerized tomography (CT) have been used successfully in many studies to measure adipose compartments of the abdomen (subcutaneous and visceral fat), anthropometrical measures like WHR and WC have been proven to be an effective measure in predicting the metabolic syndrome. WC has also been included in the metabolic syndrome definitions of the WHO, ATP Ill and new IDF.

The prevalence of obesity in both the developed and developing world have increased, which leads to diverse health outcomes and is placing a heavy burden on the economy. Abdominal obesity proved to be one of the main features in predicting metabolic and cardiovascular disease (CVD) risk and may be the link that unifies the metabolic syndrome (MS) through pro-inflammatory pathways. While the pathogenesis of the MS and each of its components are complex and not well understood, abdominal obesity remains the mechanism that relates to increased lipolysis causing the liver to increase blood glucose and very low lipoprotein output. This in turns leads to raised blood glucose, triglycerides, low-density lipoprotein cholesterol (LDL-C), blood pressure and inflammatory markers (C-reactive protein, interleukin-6 and tumor necrosis factor-a) and decreased high-density lipoprotein cholesterol (HDL-C). Prevention of the metabolic syndrome and treatment of its main characteristics are now considered of utmost importance in order to combat the increased CVD risk and all-cause mortality. Decreasing sedentary behaviour through regular physical activity is a key element in successful treatment of obesity through an increase in energy expenditure, but the ability to decrease low-grade systemic inflammation may be an even greater outcome. Aims The aims of this study was firstly, to determine by means of a literature review, how obesity could be related to a state of chronic systemic inflammation (increased CRP and IL-6). Secondly to determine whether physical activity could serve as a suitable method to decrease inflammation associated with obesity and related disorders. Thirdly to determine if abdominal obesity is a predictor of the metabolic syndrome and CVD and finally, to determine if measures of obesity can predict risk for the metabolic syndrome and CVD risk. Methods For this review study, a computer-assisted literature search were utilized to identify research published between 1990 and 2005. the following databases were utilized for the search: NEXUS, Science Direct, PubMed and Medline. Keywords related to obesity (abdominal obesity, overweight), metabolic syndrome (insulin resistance syndrome, dysmetabolic syndrome, syndrome X), cardiovascular disease (coronary heart disease, coronary artery disease), cardiovascular risk factors (hypertension, dyslipidemia, diabetes mellitus, physical activity), inflammatory markers (CRP, IL-6, chronic low-grade inflammation) and physical activity (fitness, exercise and training) were included as part of the search, including the references identified by previous reviewers (not identified as part of the computerized literature search). Results and conclusions Several research studies concluded that obesity could be an inflammatory disorder due to low-grade systemic inflammation. Adipose tissue is known to be a sectretory organ producing cytokines, acute phase reactants and other circulating factors. The synthesis of adipose tissue TNF-a could induce the production of IL-6, CRP and other acute phase reactants. CRP is a acute phase reactant, synthesized primarily in hepatocytes and secreted by the liver in response to a variety of inflammatory cytokines of which IL-6 and TNF-a are mainly involved. CRP increases rapidly in response to trauma, inflammation and infection. Thus, enhanced levels of CRP can be used as a marker of inflammation. Several studies of large population cohorts provide evidence for an inverse, independent dose-response relation between plasma CRP concentration and level of physical activity in both men and women. Trends for decreased IL-6, TNF-a and CRP concentrations were linear with increasing amounts of reported exercise in most of the research studies, physical activity proved effective in lowering measures of adiposity (BMI, WHR, WC and percentage body fat) and obesity related inflammatory markers (CRP & IL-6). Thereby indicating a potential anti-inflammatory effect. In the studies reviewed in this article abdominal obesity is identified as a predictor and independent risk factor for CVD in both men and women. High levels of deep abdominal fat have also been correlated with components of the metabolic syndrome, glucose intolerance, hyperinsulinemia, hypertension, diabetes, increases in plasma triglyceride levels and a decrease in HDL-C levels (dyslipidemia) in many of the studies. Prospective epidemiological studies have revealed that abdominal obesity (determined by WC and WHR) conveys an independent prediction of CVD risk and is more relevant compared to general obesity (determined by BMI). Abdominal fat has been linked to metabolic risk factors like high systolic blood pressure, atherogenic dyslipidemia, with increased serum TG and decreased HDL-C, and glucose intolerance. Although magnetic resonance imaging (MRI) and computerized tomography (CT) have been used successfully in many studies to measure adipose compartments of the abdomen (subcutaneous and visceral fat), anthropometrical measures like WHR and WC have been proven to be an effective measure in predicting the metabolic syndrome. WC has also been included in the metabolic syndrome definitions of the WHO, ATP Ill and new IDF.