12 main causes of obesity - Epidemiological determinants

12 main causes of obesity

OBESITY: 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. 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. It is useful therefore, to be able to distinguish between those at increased risk as a result of "abdominal fat distribution" or "android obesity" from those with the less serious "gynoid" fat distribution, in which fat is more evenly and peripherally distributed around the body.

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 increase 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.

The aetiology of obesity is complex, and is one of multiple causation:

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. Hyperplastic obesity in adults is extremely difficult to treat with conventional methods.

Ethnic groups in many industrialized countries appear to be especially susceptible to the development of obesity and its complications. Evidence suggests that this may be due to a genetic predisposition to obesity that only become apparent when such groups are exposed to a more affluent lifestyle.

There is a genetic component in the aetiology 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 per cent 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 per cent of the individual differences.

There is convincing evidence that regular physical activity is protective against unhealthy weight gain. Where as 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 morbildity 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 aetiology of obesity than used to be thought.

The relationship of obesity to social class has been studied in some detail. There and clear direct relationship between socio-economic status and obesity. Within some affluent countries, however, obesity has been found to be more prevalent in the lower socio-economic groups.

Eating habits (e.g., eating in between meals, preference to sweets, refined foods and fats) are established very early in life. The composition of the diet, the periodicity with which it is eaten and the amount of energy derived from it are all relevant to the aetiology of obesity. A diet containing more energy than needed may lead to prolonged post-prandial hyperlipidaemia 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. 

The consumer demand by itself may be influenced by advertising, marketing, culture, fashion and convenience. It has been calculated that a child whose energy requirement is 2000 kcal/day and who consumes 100 kcal/day extra will gain about 5 kg a year. The accumulation of one kilo of fat corresponds to 7,700 kcal of energy.

Psychosocial factors (eg, emotional disturbances) are deeply involved in the aetiology 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 the obesity has developed is essential for planning the most suitable management.

Obesity frequently runs in families (obese parents frequently having obese children), but this is not necessarily explained solely by the influence of genes.

These may be involved in occasional cases, e.g., Cushing's syndrome, growth hormone deficiency.

A recent review of studies concluded that the relationship between alcohol consumption and adiposity was generally positive for men and negative for women.

In most affluent societies, there is an inverse relationship between educational level and prevalence of overweight.

Reports that the use of tobacco lowers body weight began to appear more than 100 years ago, but detailed studies have been reported only during the past 10 years or so. In most populations, smokers weigh somewhat less than ex-smokers; individuals who have never smoked fall somewhat between the two.

Use of certain drugs, e.g., cortico-steroids, contraceptives, insulin, ẞ-adrenergic blockers, etc. can promote weight gain.