in the range of 20–25 as optimum may result in neglecting all the increasing comorbidities of weight gain within this “acceptable” range. These issues will be considered in greater detail later when we consider the overall hazards of obesity.
Obesity epidemic starts in the early 1980s
Data from the United States suggests that mean population BMI was increasing consistently across the decades from the early 1900s, but the level of overweight and obesity, as defined by a BMI of 25 and 30, only began to increase rapidly in the early 1980s [11]. The Organization for Economic Cooperation and Development (OECD) report on obesity showed that in the 1970s the overall US adult obesity prevalence was already 14% for all adults, but it has risen progressively since then and continued to increase in the 2010s to above 35%. Similar patterns were seen in other developed countries. National surveys of English adults in the 1930s and 1940s reported obesity rates less than 5% in those below the age of 40 years but increasing to 10% in the 50‐year‐old men. Detailed national representative surveys in England in 1981 showed that overall obesity rates remained relatively low (6% in men aged 16–65 years and 8% in women) [12], but obesity rates had already risen to 11–12% in 40–60‐year‐olds. Similar prevalences were found in studies in Finland (albeit those data were self‐reported), and the Netherlands also reported an average adult prevalence of 5%, but measured prevalence data from Japan on average showed that only 2% adults with obesity.
From the early 1980s, it is clear that obesity prevalences were starting to increase in all Western societies, and by the late 1980s, upper‐middle‐income countries were beginning to follow the North American and European countries, with increasing obesity rates evident in both men and women from the age of 20 upwards. The pivotal importance of this early part of the 1980s in setting new trends of increasing obesity was vividly illustrated by Norton and others’ analysis of children’s weights and heights measured in community and other population surveys in Australia over a whole century [13]. By using the IOTF’s BMI criteria for childhood obesity [14] (which linked seamlessly with the adult BMI cut‐off points), Norton’s analysis showed that there was very little increase in childhood obesity until the early 1980s when a remarkable increase started to develop. These IOTF cut‐offs have subsequently been refined [15], but the overall picture and analyses are unchanged and reveal something very unusual changed in the environment from the early 1980s onward in affluent societies, with middle‐income countries revealing the beginning of a rise in BMIs a little later.
The global epidemic gets underway
The trends in obesity rates from the 1980s to 2008 were beautifully illustrated by Finucaneand others [16] in a comprehensive analysis of huge data sets from around the world, as shown in Figure 1.1. The data reveal marked differences in the prevalences of males and females. In males, it is clear that the more affluent a society in 1980 then the greater the likelihood of some obesity. Thus North America, Latin America, Australia, and Europe had overall prevalences of 10% obesity. In general, the greater the degree of regional affluence, the greater the increase in obesity rates in men over the subsequent 28 years. However, in the early 1980 data, the highest level of obesity among women was not found in North America but rather in emerging counties in Southern Africa, North Africa, the Middle East, and Central Latin America, with Asian women having the lowest levels. In the following three decades, the 1980 regional ranking in women was generally preserved with the fattest regions showing the most significant increases in obesity so that by 2008 several regions of the world were approaching a 40% prevalence of obesity in women.
Since these comprehensive analyses of obesity prevalences, there has been a series of updates both by the Ezzati and Murray groups [17] supported by the Gates Foundation and by the OECD [18] with updates [19] – as well as by a range of national expert groups [20,21]. These data stimulate the question as to why this epidemic had become so striking and seemingly resistant to change and, indeed, how might the problem be tackled? This resistance to change is evident, for example, from surveys conducted by Public Health England who showed that 40% or more of men and over 50% of women aged 25–74 years were trying to lose weight in 2016 [22] and yet the obesity rates remain high suggesting that under current circumstances individuals attempt to slim is very ineffective as a population strategy.
Using historical records, Jaacks and others [23] then examined the evolution of obesity and highlighted four phases in the chronological development of obesity:
Stage 1. Obesity is more prevalent in women than in men and is evident in more affluent groups with low prevalence rates in children. This phase is still evident in many South Asian countries and sub‐Saharan Africa.
Stage 2. In stage 2 of the transition, there has been a significant increase in the adult obesity rates with less of a gap between the sexes and in terms of socioeconomic differences. Many Latin American and Middle Eastern countries are at this stage.
Stage 3. In this stage, a swing occurs with those of lower socioeconomic status now having a higher obesity prevalence, but the more affluent women and children do not show any further secular increase. These features are evident in Europe.
Stage 4. This stage is where obesity prevalence actually declines but is a phenomenon we have yet to observe.
In within‐country analyses, higher rates of obesity are traditionally associated with urban environments, but Ezzati and colleagues have highlighted that more recently there has also been a marked increase in rural obesity [24]. This implies that the drivers of obesity were originally most evident in urban areas, but as the world has developed, the factors promoting obesity have penetrated the rural communities and/or the rural environment has lost some of the factors which limited the development of obesity.
Abdominal obesity
So far, we have only been considering analyses of obesity epidemiology in terms of BMI, but as previously mentioned, Asian physicians have long been concerned by the onset of obesity’s comorbidities at much lower BMIs than in Western Europe or North America. The long‐standing clinical observation that abdominal obesity was particularly hazardous had led to Vague’s identifying decades ago that there was a particular risk if a patient had an android phenotype as distinct from a gynecoid pattern of fat distribution with a small waist/hip (W/H) ratio [25]. The likelihood that abdominal obesity was associated with additional risk was widely accepted, but the definition of what constituted abdominal obesity was uncertain except in terms of a high W/H ratio (>1). The Scottish Royal Colleges of Physicians were preparing a simple guide for general practitioners in 1993 on how to tackle obesity and sought to have the assessment and management summarized on a single page chart which could be placed on a GP’s consulting room table. This necessitated a numerical definition of what normal waist measurements were and what the cut‐offs should be for specifying abdominal obesity. Based on the data from a population survey of adults in the Netherlands, Mike Lean and Jaap Seidel decided to simply take the waist measurements of 94 and 102 cm in men and 80 and 88 cm in women since these values corresponded epidemiologically to BMIs of 25 and 30 in the Dutch population [26]. They also noted that values exceeding these waist circumferences were associated with higher cardiovascular risks. These values were therefore taken as the cut‐off points for abdominal obesity in the Scottish Intercollegiate Guidelines Network (SIGN) guidelines [27] and were then promptly incorporated by the National Institute of Health (NIH) group into their US guidelines for tackling obesity [28] as well as being used in the draft IOTF report for WHO, and then incorporated as the cut‐off points in the report of the first WHO Expert Technical Committee to deal with obesity [5].
