Is the obesity epidemic exaggerated? No

Abstract

The UK health secretary declared last week that we are in the grip of an obesity epidemic. Patrick Basham and John Luik believe that the problem is less clear cut, but R W Jeffery and N E Sherwood say that obesity is a growing global problem

An abundance of observational and experimental data show the growing prevalence of obesity, defined as a body mass index ≥30, and the causal role of obesity in adverse health outcomes. These data substantiate our position that the seriousness of the obesity epidemic is not exaggerated. The fact that obesity is developing rapidly in many parts of the globe is incontrovertible. The World Health Organization’s Global Database on Body Mass Index includes the most comprehensive international data available on obesity trends.¹ Absolute prevalence of obesity varies among countries (0.7%- 78.5%). However, large rises in prevalence have been observed across the globe over the past few decades. Rates of obesity in adults have roughly tripled in Japan (from 0.84% in 1980 to 2.86% in 2001), Brazil (from 2.4% in 1974-5 to 8.9% in 2002-3), England (from 6.2% in 1982 to 22.6% in 1999), the United States (from 11.5% in 1990 to 34.1% in 2004), and Seychelles (from 4.2% in 1989 to 15% in 2004) to give a few examples.¹

The prevalence of obesity among children and adolescents has also increased greatly. The US National Health and Nutrition Examination Survey indicates that the prevalence of obesity in 1976-80 was 6.5% among 6-11 year olds and 5% among 12-17 year olds. In 2003-4 it was 19% and 17% respectively. These disturbing trends are mirrored in other countries. Prevalence of overweight among school age children has been reported as high as 35% in parts of Europe, and it has been estimated that the European Union can expect to see the numbers of overweight and obese children rising by around 1.3 million a year by 2010.² A recent review of childhood obesity trends from 25 countries with data on school age children and 42 countries with data on preschool populations shows that obesity has increased in most countries, with the sharpest increases in economically developed countries and urban areas.³

Health effects

The adverse effects of obesity on health are well established, serious, and causal. Overweight and obesity increase the risk of many serious health conditions, including hypertension, hypercholesterolaemia, diabetes, coronary heart disease, and some forms of cancer.⁴,⁵,⁶,⁷,⁸,⁹ A dose-response relation between body mass index and the risk of developing chronic diseases is even observed among adults in the upper half of the “healthy” weight range (that is, body mass index of 22.0-24.9).⁶

Increases in body weight are strongly associated with increased insulin resistance at the cellular level, which may be a fundamental mechanism driving many disease processes. Three large clinical trials have shown that behavioural interventions targeting weight reduction and physical activity in people with impaired glucose tolerance improve the natural course of diabetes.¹⁰,¹¹,¹² Lifestyle change with a 7% weight loss delayed the development of type 2 diabetes in high risk individuals by 58% over four years compared with the control group.¹²

Because effective, sustained weight loss is not easily achieved clinically or by traditional public health education measures,¹³,¹⁴ we are facing the potential for a major health crisis. When will the obesity driven health crisis arrive and how serious it will be has been the subject of much speculation. Not all diseases related to obesity have paralleled obesity trends. For example, the incidence of cardiovascular disease incidence has fallen steeply as body weight has risen, perhaps because of improvements in diet or better treatments for risk factors such as raised blood pressure and blood lipid concentrations.

However, examination of trends in the disease most strongly linked to obesity, diabetes, is very concerning. Data from the Behavioral Risk Factor Surveillance System and the National Ambulatory Medical Care Survey (1995-2004) show that during a period in which the prevalence of overweight and obesity increased by nearly 24%, the prevalence of diabetes increased by about 76% and the number of diabetes related visits to primary care doctors more than doubled.¹⁵

Health economists and epidemiologists have made projections about the potential impact of future obesity trends. Most agree that the contribution of obesity to current healthcare costs is high and that it is likely to get much higher.¹⁶,¹⁷,¹⁸ Some have argued that we may even see real falls in life expectancy within a few decades.¹⁹

In summary, a large body of scientific evidence documents that overnutrition and obesity are a major global health problem. With the continuing rise in obesity and limited treatment efficacy, options for averting a poor public health outcome seem to rest either on the hope that scientists are wrong in their projections or speedy investment in the development of more effective public health measures to deal with it. We think the second option a more prudent scientific and policy choice.