Body mass index (BMI) is calculated by dividing weight in kilograms (kg) by the square of height in metres (m).
BMI>25 = overweight
BMI 25-29.9 = pre-obesity
BMI>30 = obesity
The sub-categories of obesity:
Obesity class I: 30.0-34.9 = moderate
Obesity class II: 35.0-39.9 = severe
Obesity class III: 40+ = very severe
Source: World Health Organization. Obesity: Preventing and Managing the Global Epidemic. Technical Report Series no. 894. WHO, Geneva, 2000.
The term 'ischaemic' means that an organ, in this case the heart muscle, has not received enough blood and oxygen. People with this condition have weakened heart pumps, either due to previous heart attacks or due to current blockages of the coronary arteries.
"A new generation is entering adulthood with unprecedented levels of obesity. This, in addition to the existing burden of adult obesity, reinforces the concern that weight-related chronic diseases will be the most significant public health concern throughout the 21st century."
Obesity is one of the principal risk factors for type 2 diabetes. An excess of body fat, especially when concentrated within the abdomen, has a range of potentially harmful consequences. Classified as a disease, obesity diminishes both quality of life and life expectancy, but it is also a common risk factor for a number of other diseases from osteo-arthritis to heart disease and some types of cancer.
Overweight and obesity lead to adverse metabolic effects on blood pressure, cholesterol, triglycerides and insulin resistance. Risks of coronary heart disease, ischaemic stroke and type 2 diabetes increase steadily with increasing body mass index (BMI). Type 2 diabetes - confined to older adults for most of the 20th century - now affects some obese children even before puberty. Modest weight reduction reduces blood pressure and abnormal blood cholesterol and substantially lowers risk of type 2 diabetes.
Obesity and type 2 diabetes are causally linked. Weight gain leads to insulin resistance through several mechanisms. Insulin resistance places a greater demand on the pancreatic capacity to produce insulin, which also declines with age, leading to the development of clinical diabetes. Physical inactivity, both a cause and consequence of weight gain, also contributes to insulin resistance.
Analyses by the International Obesity Task Force (IOTF), undertaken for the World Health Report 2002 and associated WHO Global Burden of Disease research, indicate that approximately 58% of diabetes mellitus globally can be attributed to BMI above 21 kg/m2. However in western countries, around 90% of type 2 diabetes cases are attributable to weight gain, as shown in the figure below, and childhood overweight and obesity are now leading to an unusual pattern of premature type 2 diabetes, which is particularly difficult to manage once established1James WPT, Jackson-Leach R, Mhurdu CN, Kalamara E, Shayeghi M, Rigby N, Nishida C and Rodgers A. Overweight and Obesity. In Comparative Quantification of Health Risks: Global and Regional Burden of Disease Attributable to Selected Major Risk Factors, eds. Ezzati M, Lopez AD, Rodgers A, Murray CJL. WHO, Geneva, 2003..
Childhood obesity is a relatively recent phenomenon, which poses a critical threat to health. Significant prevalences exist in both developing and developed countries. An IOTF analysis (see figure below) has shown that overweight and obesity affects one in 10 children worldwide, but the rate is double in Europe and three times as great across the entire Americas2IOTF. Childhood Obesity - The New Crisis in Public Health. International Obesity Task Force, London, 2003. . The emergence of type 2 diabetes in childhood is a serious development. In the USA it has been noted that up to 45% of children with newly diagnosed diabetes have type 2 diabetes and most are overweight or obese at diagnosis3American Diabetes Association. Type 2 diabetes in children and adolescents. Diabetes Care 2000; 3:381-389..
Among adults, clear evidence exists that surprisingly modest weight reductions can markedly reduce the development of type 2 diabetes, if not prevent it completely, in susceptible individuals, and that weight loss can reverse the type 2 diabetic state. The remarkable effect of weight loss through diet and increased activity has been demonstrated in the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) Diabetes Prevention Programme in the USA to benefit particularly the over-60s, in whom nearly three-quarters of new cases of diabetes were prevented.
This and other studies provide hope to those with impaired glucose tolerance (IGT) and a susceptibility to diabetes. Dietary and activity changes to produce a 5-7% weight loss can successfully reduce the incidence of type 2 diabetes; reductions in fat and calorie intake accompanied by half an hour's extra walking or other exercise each day have been demonstrated to lower the incidence by 58%. Great success has been achieved among people over 60 years, reducing the development of diabetes in that high-risk age group by 71%4Knowler WC, Barrett-Connor E, Fowler SE, Hamman RF, Lachin JM, Walker EA, Nathan DM. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med 2002; 346:393-403.. Similar data have emerged from China, Scandinavia and other European studies.
WHO recommendations for dietary improvements and increased levels of exercise across entire populations provide the basis for the development of global strategies to challenge the rise in obesity along with other diet and activity related chronic diseases, including type 2 diabetes5WHO/FAO. Diet, Nutrition and the Prevention of Chronic Diseases. Technical Report Series no. 916. WHO, Geneva, 2003. (www.who.int/hpr/NPH/docs/who_fao_expert_report.pdf). However even if the WHO recommendations, including those to reduce fat, sugar and salt consumption, were to be implemented, it would be some considerable time before the benefits were reflected in a reduction of obesity and co-morbidity rates.