Better nutrition is associated with better growth. It is also well appreciated that the nutritional status of children in adolescents is a determinant of health and disease. Both underweight and overweight are associated with health consequences. Over the past century, most nutrition research and indeed, nutrition policy in low and middle income countries has focused on poverty and its impacts on under nutrition. There is however now evidence of a major shift towards overweight and obesity in these same societies. The dramatic increase in the proportion of adults who are over their healthiest weight in high income countries is now being well documented. And this same trend is increasingly apparent in children and adolescents including those in low and middle income countries. Understanding trends in child and adolescent obesity is important. As well as understanding how obesity and overweight track across childhood, adolescents and adulthood. This is because obesity in adolescence has many adverse effects on health in both adolescence and later adulthood as well has for the next generation in terms of the epigenetic risks of obesity. We've seem this study before from Shandong Province, China in the last lecture. But in this time, I'm just wanting to use it to illustrate the growth of overweight and obesity or the increasing trends in overweight and obesity. Again, it's a study of school-aged population, aged 7 to 17 years of age, that was studied over the 20 year period from 1995 to 2005. Data were derived from two national surveys of student health, and they measured height, body weight, body mass index, reported by, these age groupings here. Prevalence of underweight, overweight, and obesity were categorised according to body mass index, and as we heard in the last lecture, anemia was also measured. The results here show that there was increased stature at each of these ages, ranging in males an increase from 1.95 to 3.66 centimetres at each time point or age point. And in females an increase of a mean from 1.4 to 2.91. Clearly Chinese children and adolescents have gotten taller over this period, and in the latter ten years underweight and anaemia were far less significant as we've previously shown. However what we'll show on subsequent slides as well, is that the proportion of the population that was overweight and obese increased over the same time. These data are consistent with a striking change seen across the globe. Overweight and obesity are now linked to more deaths worldwide than underweight. According to the World Health Organization, 65% of the world's population lives in countries where over overweight and obesity kill more people than underweight. This includes all high income and most middle income countries. Once considered a problem only in high income countries, overweight and obesity is now dramatically on the rise in low and middle income countries as well, particularly in urban settings. What this means is that today nearly 30% of the world's population is either obese or overweight. The rise in global obesity rates over the last three decades has been widespread but also substantial. And it now represents a major public health epidemic in both the developed and the developing world. Worldwide, there are rising rates of adiposity, a term that refers to the amount of body fat in adults. The graph shows data from 1980 and 2013. And we can see substantial increases in the proportion of the adult population that is both overweight, and obese. We're not just getting fat, we're getting fatter, and these data show that over one third of adults are now either overweight or obese. Some countries have more of a problem with adult obesity than others. For example, the estimated prevalence of obesity exceeded 50% in men in Tonga, and women in Kuwait, Tonga, Kiribati, Federated States of Micronesia, Libya, Qatar and Samoa. These are extraordinary figures, 50% or more with obesity. Now there is some good news, in that since about 2006, it would appear that the increase in adult obesity in a number of developed countries has started to slow down. Overweight and obesity are defined as abnormal or excessive fat accumulation that presents a risk to health. A crude population measure of obesity is the body mass index or BMI, a person's weight in kilograms divided by the square of his or her height in meters. A person with a BMI of 30 or more is generally considered obese, while a person with a BMI equal to or more than 25 is considered overweight. And these cutoffs are shown here on the chart. However, as you can see, BMI changes substantially from birth through adolescence. It's not fixed as it is in adulthood in terms of normative values. At birth, the median BMI is as low as 13 kilograms per meter squared. It increases then to 17 at age one decreasing to 15.5 at age six, and again increasing to 21 kilograms per meter squared at the age of 20. Given these effects of growth, a cut off point related to age is also needed to define obesity in children and adolescents. And in this regard, reference centiles have been developed for this purpose developed by the International Obesity Taskforce, with standard definitions. While there may be evidence of some slowing in the secular trends of overweight and obesity in the developed world in adults, this is not the case in children and adolescence where the trends are even more striking than in adults as shown here. Developed country data is shown on the left half while the right half shows the same trends in developing countries. Males are in blue and females are in red. Between 1980 and 2013, the prevalence of overweight or obese children and adolescents increased by nearly 50%. In 2013, more than 22% of girls and nearly 24% of boys living in developed countries were overweight or obese. Rates are also on the rise among children and adolescents in the developing world, where around 13% of both boys and girls are overweight or obese. Particularly high rates of child and adolescent obesity are seen in Middle Eastern and North African countries, notably among girls. Let's look in detail at some of these circular trends. The data here on again 7-17 year old males from a series of large representative studies from Shandong, again this highly populous province of Southern China. We can see a very dramatic upswing in both the proportion of boys who are overweight. That's the pale blue here ranging from 1985 to 2010 as well as those who are obese, shown in the dark blue. There is yet to appear to be any slowing of these trends. And on this slide, we can compare the rates of overweight and obesity in males on the left compared to females on the right. As you can see the prevalence of overweight and obesity is significantly higher In males than in females. Why do you think this might be the case? You may want to pause to think about this. Apart from sex, it is apparent that there are also social determinants of weight. Staying with the region of Shandong, China, the same authors explored the association of overweight and obesity wIth socioeconomic status or SES. This was a large study. The authors surveyed over 42,000, 7 to 18 year old students from 16 districts. And in addition to measuring their height and weight with prevalence rates of obesity and overweight determinant using International Obesity Task Force cutoffs, the authors then assigned each of the 16 districts a socioeconomic status ranking of low, medium, or high based on per capita GDP and income in rural and urban areas. They showed significant differences by SES group for height, weight, and the prevalence of overweight and obesity. Boys and girls from high socioeconomic status groups were taller, heavier, and more likely to be obese than their peers in moderate or low-ranking socioeconomic status groups, as shown in this figure with more striking effects in boys. These changes are thought to reflect variations within the process of urbanisation, with dramatic increases in dietary fat intake, equally dramatic reductions in physical activity, and changes in both public health and living environments. So, in low and middle income countries, just like in China, levels of obesity are higher in higher socioeconomic groups. But in high and middle income countries, this relationship is reversed. For example, in this study from 2002, income turtiles were used to indicate low, medium, and high income levels comparing data in surveys from different countries over a 20 year period. I've shown here the panels for Brazil on the left and for the United States on the right, that show these opposing patents of overweight by income such that in Brazil, those from the highest SES are the most overweight. Whilst in the United States, those from the lowest SES groups are the most overweight. Now obesity in North Africa and the Middle East is a notable health issue. Urbanisation has occurred rapidly, accompanied by new technologies that promote more sedentary lifestyles. Due to the accessibility of cars, and highway infrastructure as shown here, the rise of television, the rise of household appliances, the population as a whole is engaging in far less physical activity. Which isn't helped by a hot climate and poor public transport infrastructure. The dramatic rise in caloric and fat intake, in a region where exercise is not a defining part of the culture, is no doubt another factor. But in comparison to gender patterns in China, where overweight and obesity is more common in adolescent boys. Overweight is higher among young women in many countries in the Middle Eastern North America. Why do you think this might be the case? In these countries, like in all countries, there are cultural norms and perceptions of appropriate female behavior and occupations inside and outside the home. A majority of women do not have jobs outside the home and lead more sedentary lifestyles as a result. Housework is often the only source of physical activity for women, as there is no tradition of female participation in sports. And there's perhaps also poor knowledge about the health consequences of obesity, another contributing factor. But you may be aware of a whole range of other factors. Which I would be encouraging you to share with us.
