Obesity

Obesity is a condition that is influenced by genetic and environmental factors (such as energy intake and expenditure, fetal nutrition, culture). There are four major physiological causes of obesity: endocrine disorders (growth hormone deficiency, Cushing syndrome), genetic syndromes (Prader-Willi syndrome or Alstrom syndrome), disorders of the central nervous system (tumor, trauma) or the most common cause, multifactorial or primary obesity (caused by an interaction of multiple genes).

A number of metabolic functions can be affected by genetic background and result in a variable production, storage, and distribution of body fat among different people. Therefore, some people are more susceptible to obesity than others. Although obesity appears to run in families, the twin studies have indicated that only 50% of the tendency for obesity is inherited, the rest is contributed by the environment. Although at present, environmental factors responsible for the weight imbalance are obscure, an imbalance between energy intake (diet) and energy output (exercise and energy demands of the body) appears as a main problem resulting in surplus body fat. Energy output is related to the level of physical activity undertaken by a person. People engaging in regular exercise are likely to loose or not gain weight over time, while a reduction in physical activity brought about by an increase in inactive lifestyle (TV watching, computer games, etc.) leads to weight gain. The changes in lifestyle affect energy intake. An increase in consumption of fat and sugar-containing foods results in overeating, as those foods have poor satiating capacity. It is clear that the combination of bad dietary habits and low exercise levels increases the risk of obesity and related diseases. This risk is increased in people with lower metabolic rates. Metabolism, defined as the sum total of all the chemical reactions occurring within the cells of the body, can be affected by thyroid hormone levels, growth hormone levels, and insulin levels. Some researchers suspect that imbalances in these hormones can cause obesity. An important cause can also be a malfunction in the hypothalamus region of the brain that regulates appetite and satiety. Satiety is a feeling of satisfaction after eating. If the hypothalamus malfunctions, an individual may not experience feelings of fullness after eating, and overeat as a result feeling constantly hungry. Moreover, it appears that fetal development and nutrition can have an influence on development of obesity later in life. It has been suggested that maternal malnutrition leads not only to low birthweight, but also to an increased risk of developing obesity postnatally.