The obesity epidemic is not restricted to industrialized societies; this increase is often faster in developing countries than in the developed world. Obesity and overweight pose a major risk for serious diet-related chronic diseases, including type 2 diabetes, cardiovascular disease, hypertension and stroke, and certain forms of cancer. The health consequences range from increased risk of premature death, to serious chronic conditions that reduce the overall quality of life. Of especial concern is the increasing incidence of child obesity.

Causative factors
Obesity is generally a result of a combination of factors:
• Genetic predisposition
• Energy-rich diet
• Limited exercise and sedentary lifestyle
• Underlying illness (e.g. hypothyroidism)
• An eating disorder (such as binge eating disorder)
• Stressful mentality (debated)


How do we define obesity and overweight?

The prevalence of overweight and obesity is commonly assessed by using body mass index (BMI), defined as the weight in kilograms divided by the square of the height in metres (kg/m2). A BMI over 25 kg/m2 is defined as overweight, and a BMI of over 30 kg/m2 as obese.These markers provide common benchmarks for assessment, but the risks of disease in all populations can increase progressively from lower BMI levels. Adult mean BMI levels of 22-23 kg/m2 are found in Africa and Asia, while levels of 25-27 kg/m2 are prevalent across North America, Europe, and in some Latin American, North African and Pacific Island countries. BMI increases amongst middle-aged elderly people, who are at the greatest risk of health complications. In countries undergoing nutrition transition, overnutrition often co-exists with undernutrition. People with a BMI below 18.5 kg/m2 tend to be underweight.

How does excess body fat impact health?

Overweight and obesity lead to adverse metabolic effects on blood pressure, cholesterol, triglycerides and insulin resistance. Some confusion of the consequences of obesity arise because researchers have used different BMI cut-offs, and because the presence of many medical conditions involved in the development of obesity may confuse the effects of obesity itself. The non-fatal, but debilitating health problems associated with obesity include respiratory difficulties, chronic musculoskeletal problems, skin problems and infertility. The more life-threatening problems fall into four main areas: CVD problems; conditions associated with insulin resistance such as type 2 diabetes; certain types of cancers, especially the hormonally related and large-bowel cancers; and gallbladder disease. The likelihood of developing Type 2 diabetes and hypertension rises steeply with increasing body fatness. Confined to older adults for most of the 20th century, this disease now affects obese children even before puberty. Approximately 85% of people with diabetes are type 2, and of these, 90% are obese or overweight. And this is increasingly becoming a developing world problem. In 1995, the Emerging Market Economies had the highest number of diabetics. If current trends continue, India and the Middle Eastern crescent will have taken over by 2025. Large increases would also be observed in China, Latin America and the Caribbean, and the rest of Asia.

Raised BMI also increases the risks of cancer of the breast, colon, prostrate, endometroium, kidney and gallbladder. Chronic overweight and obesity contribute significantly to osteoarthritis, a major cause of disability in adults. Although obesity should be considered a disease in its own right, it is also one of the key risk factors for other chronic diseases together with smoking, high blood pressure and high blood cholesterol. In the analyses carried out for World Health Report 2002, approximately 58% of diabetes and 21% of ischaemic heart disease and 8-42% of certain cancers globally were attributable to a BMI above 21 kg/m2. For information on dieting, please refer to this section.