The Global Epidemic of Obesity: An Overview

Abstract

For centuries, the human race struggled to overcome food scarcity, disease, and a hostile environment. With the onset of the industrial revolution, the great powers understood that increasing the average body size of the population was an important social and political factor. The military and economic might of countries was critically dependent on the body size and strength of their young generations, from which soldiers and workers were drawn. Moving the body mass index (BMI) distribution of the population from the underweight range toward normality had an important impact on survival and productivity, playing a central role in the economic development of industrialized societies ( 1 ). Historical records from developed countries indicate that height and weight increased progressively, particularly during the 19th century. During the 20th century, as populations from better-off countries began to approach their genetic potential for longitudinal growth, they began to gain proportionally more weight than height, with the resulting increase in average BMI. By the year 2000, the human race reached a sort of historical landmark, when for the first time in human evolution the number of adults with excess weight surpassed the number of those who were underweight ( 2 ). Excess adiposity/body weight is now widely recognized as one of today's leading health threats in most countries around the world and as a major risk factor for type 2 diabetes, cardiovascular disease, and hypertension ( 3 ). This overview provides an introduction to this issue of Epidemiologic Reviews , highlighting, in historical perspective, key scientific aspects of obesity that are addressed by the 11 articles that follow. This compilation of reviews underscores the multidisciplinary nature of obesity research and the need to expand even further our scope to fully understand and confront the obesity epidemic. Until the last decades of the 19th century, developed countries were still struggling with poverty, malnutrition, and communicable diseases. These health problems were considered a major cause of low industrial productivity ( 4 ). In the first decades of the 20th century, studies of poor children indicated that dietary energy supplementation (adding sugar and fat to the usual diet) improved growth, which became an important approach to reduce malnutrition and improve industrial productivity. An influential proponent of improving health and nutrition of the working class as a means to improve overall economic productivity was Boyd-Orr ( 5 ), who later became the founding director of the Food and Agriculture Organization. A major initial goal of this organization was to increase the availability of low-cost calorie sources, primarily edible fats and sugars. Over the following decades, these efforts indeed led to major increases in the availability of dietary energy. According to the Food and Agriculture Organization, global food production by 2002 reached about 2,600 kcal per capita and is projected to reach almost 3,000 kcal by 2030 ( 6 ). Major contributors to total calories continue to be refined sugars and vegetable oils. While extreme disparities in access to adequate food availability continue to affect millions of people, there is no question that our ability to ensure stable production of dietary energy is one of the major achievements in human evolution. Although obesity did not attract the attention of the mass media until recent decades, its prevalence in industrialized countries began to increase progressively early in the last century. By the 1930s, life insurance companies were already using body weight data to determine premiums, having identified an association between excess weight and premature death. In the early 1950s, Breslow ( 7 ) proposed a direct link between the increasing prevalence of obesity and the also-increasing rates of cardiovascular disease in the US population, a theme that was reemphasized by the US government in reports in the 1960s and 1970s ( 8 ). Clear evidence of the alarming trend in obesity rates was provided by the regular, nationally representative surveys performed from the 1960s on. These data showed the continuing rise in obesity prevalence over the past 30 years ( 9 ). By the year 2000, 65 percent of the adult population had a BMI (weight/height 2 ) above 25, and 30 percent had a BMI above 30 ( 10 ). Obesity is defined as an excess of body adiposity. For practical reasons, body weight has been used as a surrogate for adiposity, which is not easy to measure in routine examinations. Until the 1970s, obesity was defined by reference to an “ideal body weight,” derived from actuarial tables compiled by the life insurance industry. A body weight within the ideal range carried a lower risk of premature death. In the 1980s, the ideal body weight approach was replaced by BMI, and the commonly used cutoffs for overweight (BMI 25–30) and obesity (BMI >30), for both men and women, were adopted to defin