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The influence of obesity and its treatment on the immune system

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INTRODUCTION

Obesity and its treatment are important public health issues in the United States and other industrialized countries. Over one-quarter of Americans are severely overweight(1) and among members of some U.S. minority groups, especially Native American, African American, and Hispanic women, the prevalence of obesity reaches 50%.(2,3) Substantial proportions of the population of other developed countries are overweight,(4) and obesity is on the rise in developing nations.(5) The high prevalence of over-weight worldwide is of concern because excess body fat can have serious health consequences. Epidemiologic studies have clearly demonstrated that overweight increases the risk for cardiovascular disease, diabetes, hypertension, cancer, gallbladder disease, and early death.(1) Weight reduction is routinely recommended to overweight individuals to decrease these risks and improve already existing obesity-related conditions. Each year, for medical as well as aesthetic reasons, 2 million overweight Americans enter structured weight reduction programs,(6) and one in four men and one in two women attempt to lose weight on their own by dieting.(7) In 1989 alone, Americans spent more than $10 billion on weight loss programs.(6) Although the health impacts of both obesity and weight reduction have been the topics of much medical research, very few investigations have focused on the immune system.

Several types of observations suggest that obesity may be associated with altered immunity. Increasing body weight and duration of obesity are strongly associated with increased overall morbidity and mortality.(1,8) Mortality from all cancers and the incidence rates of several specific types of cancer are elevated in overweight individuals.(8,9) Epidemiological and clinical survey data suggest that incidence and severity of infectious illness are higher in obese than in nonobese individuals.(10,11) Despite such findings, which suggest that immunocompetence may be altered in obesity, few studies have directly assessed specific aspects of immunity in obese humans.

Weight reduction improves many of the adverse...