Obesity may be defined as an abnormal growth of the adipose tissue due to an enlargement of fat cell size (hypertrophic obesity) or an increase in fat cell number (hyperplastic obesity) or a combination of both. Obesity is often expressed in terms of body mass index (BMI). Being overweight is usually due to obesity but can arise from other causes such as abnormal muscle development or fluid retention. However, obese individuals differ not only in the amount of excess fat that they store but also in the regional distribution of the fat within the body. The distribution of fat induced by the weight gain affects the risk associated with obesity, and the kind of disease that results.
Obesity is perhaps the most prevalent form of malnutrition. As a chronic disease, prevalent in both developed and developing countries, and affecting children as well as adults, it is now so common that it is replacing the more traditional public health concerns including undernutrition. It is one of the most significant contributors to ill health. For industrialized countries, it has been suggested that such increases in body weight have been caused primarily by reduced levels of physical activity, rather than by changes in food intake or by other factors. It is extremely difficult to assess the size of the problem and compare the prevalence rates in different countries as no exact figures are available and also because the definitions of obesity are not standardized. Overweight and obesity are the fifth leading risk of global deaths. Worldwide, obesity has more than doubled since 1980. In 2008, more than 1.4 billion adults, 20 years and older, were overweight. Of these over 200 million men and nearly 300 million women were obese. In 2012, more than 40 million children under 5 years of age were overweight. Once considered a high-income country problem, overweight and obesity are now rising in low-and middle-income countries, particularly in urban settings. Close to 30 million overweight children are living in developing and 10 million in developed countries. Childhood obesity is associated with a higher chance of obesity, premature death, and disability in adulthood. In addition, it is associated with future risk of increased breathing difficulties, increased risk of fractures, hypertension, and early markers of cardiovascular disease, insulin resistance, and psychological effects. At least 3.4 million adults die each year as a result of being overweight or obese. In addition, 44 percent of the diabetes burden, 23 percent of the ischemic heart disease burden, and between 7 to 41 percent of certain cancer burdens are attributable to overweight and obesity. Overweight and obesity are linked to more deaths worldwide than underweight. The survey shows a high prevalence of overweight in all age groups except in the 15-24 years group. Overweight prevalence was higher among females than males and in urban areas than in rural areas. Low prevalence was recorded among the lower levels of education (ill-literate and primary level), and in people whose occupation was connected with agriculture or manual work. As obesity is a key risk factor in the natural history of other chronic and non-communicable diseases, the typical time sequence of the emergence of chronic diseases following the increased prevalence of obesity is important in public health planning.
The first adverse effects of obesity to emerge in the population in transition are hypertension, hyperlipidemia, and glucose intolerance, while coronary heart disease and the long-term complications of diabetes, such as renal failure begin to emerge several years (or decades) later. It is a matter of time before the same mortality rates for such diseases will be seen in developing countries as those prevailing 30 years ago in industrialized countries.
The etiology of obesity is complex and is one of the multiple causations, obesity can occur at any age, and generally increases with age. Infants with excessive weight gain have an increased incidence of obesity in later life. About one-third of obese adults have been so since childhood. It has been well established that most adipose cells are formed early in life and the obese infant lays down more of these cells (hyperplastic obesity) than the normal infant.
Women generally have a higher rate of obesity than men, although men may have higher rates of overweight. In the Framingham, USA study, men were found to gain most weight between the ages of 29 and 35 years, while women gain most between 45 and 49 years of age i.e. at menopausal age. It has been claimed that a woman's BMI increases with successive pregnancies. The recent evidence suggested that this increase is likely to be, on average, about 1 kg per pregnancy. On the other hand, in many developing countries, consecutive pregnancies at short intervals are often associated with weight loss rather than weight gain.
There is a genetic component in the etiology of obesity. Twin studies have shown a close correlation between the weights of identical twins even when they are reared in dissimilar environments. The profile of fat distribution is also characterized by a significant heritability level of the order of about 50 percent of the total human variation. Recent studies have shown that the amount of abdominal fat was influenced by a genetic component accounting for 50-60 percent of the individual differences.
There is convincing evidence that regular physical activity is protective against unhealthy weight gain. Whereas a sedentary lifestyle particularly sedentary occupation and inactive recreation such as watching television promote it, physical activity and physical fitness are important modifiers of mortality and morbidity related to overweight and obesity. In some individuals, a major reduction in activity without the compensatory decrease in habitual energy intake may be the major cause of increased obesity, e.g. in athletes when they retire and in young people who sustain injuries, etc. Physical inactivity may cause obesity, which in turn restricts activity. This is a vicious circle. It is the reduced energy output that is probably more important in the etiology of obesity than used to be thought.
Eating habits (e.g., eating in between meals, preference for sweets, refined foods, and fats) are established very early in life. The compositions of the diet, the periodicity with which it is eaten, and the amount of energy derived from it are all relevant to the etiology of obesity. A diet containing more energy than needed may lead to prolonged postprandial hyperlipidemia and to deposition of triglycerides in the adipose tissue resulting in obesity. Nowadays television and print media is playing an important role in producing obesity by heavy advertisement of fast food outlets of energy-dense, micronutrient poor food and beverages (usually classified under the "eat least" category in diet guidelines) of multinational corporations, which influence the daily eating habits.
Psychosocial factors (emotional disturbances) are deeply involved in the etiology of obesity. Overeating may be a symptom of depression, anxiety, frustration, and loneliness in childhood as it is in adult life. Excessively obese individuals are usually withdrawn, self-conscious, lonely, and secret eaters. An insight into the circumstances in which obesity has developed is essential for planning the most suitable. The use of certain drugs, e.g., corticosteroids, contraceptives, insulin, etc. can promote weight gain.
Use of BMI to classify obesity Body mass index (BMI) is a simple index of weight-for-height that is commonly used to classify underweight, overweight, and obesity in adults. It is defined as the weight in kilograms divided by the square of the height in meters (kg/m2). For example, an adult who weighs 70 kg and whose height is 1. 75 m will have a BMI of 22.9: BMI = 70 (kg)/l. 752 (m2) = 22.9. Obesity is classified as a BMI greater than or equal to 30.0, recommended by WHO, but includes an additional subdivision at BMI 35.0-39.9 in recognition of the fact that management options for dealing with obesity differ above a BMI of 35. The WHO classification is based primarily on the association between BMI and mortality.
Prevention of obesity should begin in early childhood. Obesity is harder to treat in adults than it is in children. The control of obesity centers on weight reduction. This can be achieved by dietary changes, increased physical activity, and a combination of both. The proportion of energy-dense foods such as simple carbohydrates and fats should be reduced; the fiber content in the diet should be increased through the consumption of common un-refined foods; adequate levels of essential nutrients in the low energy diets (most conventional diets for weight reduction are based on 1000 kcal daily model for an adult) should be ensured, and reducing diets should be as close as possible to existing nutritional patterns. The most basic consideration is that the food energy intake should not be greater than what is necessary for energy expenditure. It requires modification of the patient's behavior and strong motivation to lose weight and maintain an ideal weight. Regular physical exercise is the key to increased energy expenditure. Appetite suppressing drugs have been tried in the control of obesity.
They are generally inadequate to produce massive weight loss in severely obese patients. Surgical treatments (e.g., gastric bypass, gastroplasty, jaw-wiring, to eliminate the eating of solid food have all been tried with limited success. In short, one should not expect quick or even tangible results in all cases from the obesity prevention program. Health education has an important role to play in teaching people how to reduce overweight and prevent obesity.