Epidemiology of obesity
For thousands of years obesity was rarely seen. It was not until the 20th century that it became common, so much so that in 1997 the World Health Organization (WHO) formally recognized obesity as a global epidemic. As of 2005 the WHO estimates that at least 400 million adults (9.8%) are obese, with higher rates among women than men.
As of 2008, The World Health Organization claimed that 1.5 billion adults, 20 and older, were overweight and of these over 200 million men and nearly 300 million women were obese. The rate of obesity also increases with age at least up to 50 or 60 years old.
Once considered a problem only of high-income countries, obesity rates are rising worldwide. These increases have been felt most dramatically in urban settings. The only remaining region of the world where obesity is not common is sub-Saharan Africa.
Obesity rates in Western Africa are estimated to be 10%. Rates of obesity among women are three times those found in men. In urban West Africa rates of obesity have more than doubled in the last 15 years.
The peasants in Egypt believe that fatness is proper as the “envelope for conception;” therefore, there is enough room to bear and give warmth to the child.
China is currently facing challenges of overnutrition. This is believed to be primarily due to the rapid declines in physical activity and changing dietary habits which have occurred between the 1980s and the 2000s. The decline in physical activity is attributed to increasing technology in the workplace and changing leisure activities.
In 1989 65% of Chinese had jobs that required heavy labor. This decreased to 51% in the year 2000. Combined with this has been a change to a diet higher in meat and oil, and an increase in overall available calories. Available calories per person increased from 2330 kcal/day in 1980 to 2940 kcal/day in 2002. Rates of overweight and obese adults increased 12.9% in 1991 to 27.3% in 2004.
Overall rates of obesity are below 5% in China as a whole but are greater than 20% in some cities.
Obesity has reached epidemic proportions in India in the 21st century, with morbid obesity affecting 5% of the country's population. Urbanization and modernization has been associated with obesity. In Northern India obesity was most prevalent in urban populations (male = 5.5%, female = 12.6%), followed by the urban slums (male = 1.9%, female = 7.2%). Obesity rates were the lowest in rural populations (male = 1.6%, female = 3.8%).
Socioeconomic class also had an effect on the rate of obesity. Women of high socioeconomic class had rates of 10.4% as opposed to 0.9% in women of low socioeconomic class. With people moving into urban centers and wealth increasing, concerns about an obesity epidemic in India are growing.
In Iran the prevalence of obesity was 26.3% in 2008. Prevalence of obesity was more among women (39.5%) than men (14.5%).
Using the WHO criteria Japan has the lowest rate of obesity among the OECD member countries at 3.2%. However, as Asian populations are particularly susceptible to the health risks of excess adipose tissue the Japanese have redefined obesity as any BMI greater than 25. Using this cut off value the prevalence of obesity in Japan would be 20%, a threefold increase from 1962 to 2002. A 2008 report stated that 28.6% of men and 20.6% of women in Japan were considered to be obese.
Changing lifestyles, owing to urbanisation, as well as diet issues are the main reasons for obesity in Pakistan. According to a recent study, approximately one out of four Pakistani adults (or 22.2% of individuals) are classified as obese.
In 2002, 15% of children range from 6 to 12 years of age were overweight, by gender, 15.5% of male and 14.4% of female were overweight. In the same age range, 12％ of children were obese, by gender, 14.7％ of male and 9.1％ of female were categorized as obese. In 2005, 14.9% children range from 6 to 12 years of age were overweight, where by gender, 15.85% of male and 14.02% of female were overweight. 10.3% were categorized as obese, where by gender, 10.92% of male and 9.73% were categorized as obese.
Base on these reports done, the trends were inconclusive, although with more than 10% of the age group being obese, obesity does appear to be a problem.
Between the 1970s and the 2000s, rates of obesity in most European countries have increased. During the 1990s and 2000s, the 27 countries making up the EU reported rates of obesity from 10–27% in men and from 10–38% in women.
Most recent statistics  show that, among the 19 EU Member States for which data are available, the proportion of obese people in the adult population varied in 2008/9 between 8,0% (Romania) and 23,9% (UK) for women and between 7,6% (Romania) and 24,7% (Malta) for men.
In the UK the rate of obesity has increased about fourfold over the last 30 years, reaching levels of 22-24% in 2008/9. The United Kingdom now has one of the highest rates of obesity in Europe.
|Year||Percent males obese||Percent females obese|
The number of Canadians who are obese has risen dramatically in recent years. In 2004, direct measurements of height and weight found 23.1% of Canadians older than 18 had a BMI greater than 30. When broken down into degrees of obesity, 15.2% were class I (BMI 30–34.9), 5.1% were class II (BMI 35–39.9), and 2.7%, class III (BMI > 40). This is in contrast to self-reported data the previous year of 15.2% and in 1978/1979 of 13.8%. The greatest increases occurred among the more severe degrees of obesity; class III obesity increased from 0.9% to 2.7% from 1978/1979 to 2004. Obesity in Canada varies by ethnicity; people of Aboriginal origin have a significantly higher rate of obesity (37.6%) than the national average.
In children obesity has substantially increased between 1989 and 2004 with rates in boys increasing from 2% to 10% and rates among girls increasing from 2% to 9%.
Mexico has the highest rate of obesity among OECD members.
The United States has the second highest obesity rates in the developed world. This is a long-standing phenomenon: already by 1962, 45% of adult Americans were overweight, and 13% of adult Americans were obese; these numbers were already higher than obesity rates observed in most developed countries as late as 2001-02. From 1980 to 2002, obesity rates have doubled, reaching the current rate of 33% of the adult population.
As of 2007, 33% of men and 36% of women are obese. Rates of obesity vary between social groups, with minorities and low-income individuals more likely to be overweight. The rates are as high as 50% among African American women.
Geography is a major factor. The American South has been described alternatively as "Stroke belt", "Obesity belt", or "Diabetes belt", to reflect the fact that all residents of the region have high incidences of these three conditions, compared to people of the same race/ethnicity elsewhere in the country. The lowest obesity rates of major racial/ethnic groups across 50 states are thought to be among non-Hispanic white residents of Colorado and Hawaii, at around 16%. However, these numbers are based on self-reported height and weight data and likely to be underestimated (the bias is so large that, for example, estimates of obesity that rely on self-reported data arrive at the rate of 22% among non-Hispanic white females, whereas studies that involve direct measurement show that the rate is closer to 34%.) 
The prevalence of class III obesity (BMI ≥40) has increased the most dramatically, from 1.3% in the late 1970s, to 2.9% in 1988-94, to 4.7% in 2000, to 5.7% in 2008. Among African American women, its prevalence is estimated to be as high as 14%.
The overall rate of obesity began to plateau in the '00s, but severe obesity and obesity in children continued to rise. In January 2010, a study published in the Journal of the American Medical Association found that the obesity rate for American women has remained constant over the last decade, with only small rises amongst men and children.
Obesity is one of the leading health issues in US society, resulting in about 300,000 deaths per year in the United States. About 65 percent of Americans are now considered either overweight or obese. According to National Health and Nutrition Examination Study collected between 1970s and 2004, overweight and obesity prevalence have increased steadily among all groups of Americans over the past three decades.
Oceania and the Pacific
According to self-reported and measured results of the 2007-2008 National Health Survey, 61% of Australians were overweight (above a 25 BMI), with 24% falling into the "obese" category (above a 30 BMI). Men were more likely to be overweight (67.7%) and obese (25.5%) than women (30.9% and 23.4% respectively).
Obesity in New Zealand has become an important national health concern in recent years, with high numbers of people afflicted in every age and ethnic group. In 2011/12, 28.4% of New Zealand adults were obese, a number only surpassed in the Anglosphere by the United States.
Many of the island nations of the South Pacific have very high rates of obesity. Nauru has the highest rates of obesity in the world (94.5%) followed by Samoa, the Federated States of Micronesia, and the American Samoa. Being big has traditionally been associated with health, beauty, and status and many of these beliefs remain prevalent today.
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