Economic Growth and Modernization

A key factor in the global coverage of the obesity epidemic, particularly with respect to developing and transition countries, is economic growth. Rapid urbanization, changing occupational structures and shifts in dietary structure related to socioeconomic transition all affect population mean BMI. Demographic shifts associated with higher life expectancy and reduced fertility rates, as well as shifts in patterns of disease away from infection and nutrient deficiency towards higher rates of non-communicable diseases, are other components of this so-called 'transition'.

Table 1.8 Vulnerable periods oflife for weight gain and the development of future obesity

Prenatal

Adiposity rebound (5-7 years)

Adolescence

Early adulthood

Pregnancy

Menopause

Poor growth and development of the unborn baby can increase the risk of abdominal fatness, obesity and related illness in later life. 'Adiposity rebound' describes a period, usually between the ages of 5 and 7, when BMI begins to increase rapidly. This period coincides with increased autonomy and socialization and so may represent a stage when the child is particularly vulnerable to the adoption of behaviours that both influence and predispose to the development of obesity. Early adiposity rebound may be associated with an increased risk of obesity later in life. This is a period of increased autonomy which is often associated with irregular meals, changed food habits and periods of inactivity during leisure combined with physiological changes. These promote increased fat deposition, particularly in females. Early adulthood is often associated with a marked reduction in physical activity. This usually occurs between the ages of 15 and 19 years in women but as late as the early 30s in men.

The average weight gain after pregnancy is less than 1 kg although the range is wide. In many developing countries, consecutive pregnancies with short spacing often result in weight loss rather than weight gain. Menopausal women are particularly prone to rapid weight gain. This is primarily due to reductions in activity although loss of the menstrual cycle also affects food intake and reduces metabolic rate slightly.

Effect on BMI Distribution

Improvement in the socioeconomic conditions of a country tends to be accompanied by a population-wide shift in BMI so that problems of overweight eventually replace those of underweight (Figure 1.6). In the early stages of transition, undernutrition remains the principal concern in the poor whilst the more affluent tend to show an increase in the proportion of people with a high BMI. This often leads to a situation where overweight coexists with underweight in the same country. As transition proceeds, overweight and obesity also begin to increase among the poor.

Even in affluent countries, the distribution of body fatness within a population ranges from underweight through normal to obese. When the mean population BMI is 23 or below, there are very few individuals with a value of 30kg/m2 or greater. However, when mean BMI rises above 23kg/m2, there is a corresponding increase in the prevalence of obesity. An analysis by Rose (20) of 52 communities in the large multi-country INTERSALT Study found that there is a 4.66% increase in the prevalence of obesity for every single unit increase in population BMI above 23 kg/m2 (Figure 1.7).

The'Nutrition Transition'

Generally, as incomes rise and populations become more urban, diets high in complex carbohydrates and fibre give way to varied diets with a higher proportion of fats, saturated fats and sugars. Recent analyses of economic and food availability data, however, reveal a major shift in the structure of the global diet over the last 30 years. Innate preferences for palatable diets coupled with the greater availability of cheap vegetable oils in the global economic have resulted in greatly increased fat consumption and greater dietary diversity among low income nations. As a result, the classic relationship between incomes and fat intakes has been lost, with the so-called 'nutrition transition' now occurring in nations with much lower levels of gross national product than previously. The process is accelerated by rapid urbanization (21).

The Relationship Between Undernutrition and Later Obesity

In countries undergoing transition where overnu-trition coexists with undernutrition, the shift in population weight status has been linked to exaggerated problems of obesity and associated non-communicable diseases in adults.

Recent studies have shown that infants who were undernourished in utero and then born small have a greater risk of becoming obese adults (22,23). In particular, poor intrauterine nutrition appears to predispose some groups to abdominal obesity and results in an earlier and more severe development of comorbid conditions such as hypertension, CHD and diabetes (24-26). The apparent impact of in-trauterine nutrition on the later structure and functioning of the body has become known as 'programming' and is often referred to as the 'Barker hypothesis', after one of the key researchers involved in developing this concept.

Figure 1.6 BMI distribution for various adult populations worldwide (both sexes). As the proportion of the population with a low BMI decreases there is a consequent increase in the proportion of the population with an abnormally high BMI. Many countries have a situation of unacceptably high proportions of both under- and overweight. Source: WHO (19)

Figure 1.6 BMI distribution for various adult populations worldwide (both sexes). As the proportion of the population with a low BMI decreases there is a consequent increase in the proportion of the population with an abnormally high BMI. Many countries have a situation of unacceptably high proportions of both under- and overweight. Source: WHO (19)

Figure 1.7 The relationship between population mean BMI and the prevalence of obesity, illustrating the direct association between population mean BMI and the prevalence of deviant (high) BMI values across 52 population samples from 32 countries (men and women aged 20-59 years). r = 0.94; b = 4.66% per unit BMI. Source: Rose (20)

Figure 1.7 The relationship between population mean BMI and the prevalence of obesity, illustrating the direct association between population mean BMI and the prevalence of deviant (high) BMI values across 52 population samples from 32 countries (men and women aged 20-59 years). r = 0.94; b = 4.66% per unit BMI. Source: Rose (20)

Figure 1.8 Shifts in distribution of occupations for lower income countries, 1972-1993. There has been a steady decline in employment in labour intensive agricultural occupations and a concomitant increase in employment within the less physical demanding service sector. Source: Popkin and Doak (7)

The ramifications of programming are immense for countries such as India and China where a large proportion of infants are still born undernourished. If these children are later exposed to high-fat diets and sedentary lifestyles associated with economic transition, and develop into obese adults, then it is likely that they will suffer severe consequences in the form of early heart disease, hypertension and diabetes.

Central obesity is already emerging as a serious problem in India, even at low relative weight; among non-overweight urban middle-class residents with BMI less than 25 kg/m2, nearly 20% of males and 22% of females had a high waist-to-hip ratio. In overweight subjects with a BMI over 25 kg/ m2, abdominal obesity was found in a striking 68% of males and 58% of females.

In many populations undergoing rapid modernization and economic growth, high levels of obesity are associated with high rates of NIDDM, hypertension, dyslipidaemia and CVD as well as alcohol abuse and cigarette smoking. This has been de-scibed as the 'New World syndrome' and is responsible for the disproportionately high rates of mortality in developing nations and among the dis-advantaged ethnic minority groups in developed countries.

Occupational Structure

Figure 1.8 shows the shift in the distribution of occupations that has been occurring in lower income countries during the past several decades. There has been a move towards more capital intensive and knowledge based employment that relies far less on physical activity. In China, the rapid decline in physical activity at work in urban areas has been associated with increased levels of adult obesity (27). Large shifts towards less physically demanding work have also been observed on a worldwide basis, both in the proportion of people working in agriculture, industry and services, and in the type of work within most occupations.

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