Causes of Obesity
General Causes of Modern Obesity
Thr risk factors and contributory causes of obesity - a disease of excess body fat characterised by a body mass index of 30+ - include a range of well-documented genetic and environmental factors. But the relative effect of these causes on the development of obesity, remains unclear. Before examining possible causes, note that obesity, especially severe clinical obesity like morbid or malignant obesity, carries greater risks of morbidity and premature mortality than simple overweight.
Problem 1: Diagnosing Causes For Sudden Rise in Obesity Levels
Any explanation of the root causes of the current obesity epidemic must account for its sudden appearance. Six million American adults are now morbidly obese (BMI 40+), almost twice as high as 1980 severe obesity rates, while another 9.6 million have a BMI of 35-40.
The percentage of overweight children 6-11 has nearly doubled since the early 1980's. (Source: US Census 2000; NHANES III data estimates). Thus genetic causes are unlikely to be significant. Because while a predisposition to obesity can be inherited, the fact that obesity has increased so much in the last few decades appears to discount genetics as a major main cause.
Also, the fact that each succeeding generation is heavier than the last indicates that changes in our environment are playing the key role.
Problem 2: Separating Genetic Causes From Environmental Causes
Obesity tends to run in families, suggesting a genetic link. Yet families also share common dietary, physical exercise, attitude and lifestyle habits that may also contribute to obesity. Separating these from purely genetic factors is not an easy statistical or diagnostic task.
Environmental Causes of Obesity
In view of the sudden rise in weight levels - which is a worldwide trend as reflected in the new word "globesity" - environmental factors must be the prime cause of modern obesity.
Overconsumption - A Possible Root Cause
Eating too many calories for our enery needs must be a major candidate for the main cause of the modern obesity epidemic. According to Dr. Marion Nestle, Professor and Chair of the Department of Nutrition and Food Studies at New York University, US agribusiness now produces 3,800 calories of food a day for every American, 500 calories more than 30 years ago but at much lower per-calorie costs. Increases in consumption of calorie-dense foods, as evidenced by the growth of fast-food chains and higher soft drink consumption, also point to a higher energy-intake.
Eating Too Many High-Fat or Refined Sugary Foods
The type of food eaten may also play an important role in the rise of obesity. Researchers continue to discover more metabolic and digestive disorders resulting from overconsumption of trans-fats and refined white flour carbohydrates, combined with low fiber intake.
These eating patterns are known to interfere with food and energy metabolism in the body, and cause excessive fat storage. Associated health disorders include insulin resistance, type 2 diabetes as well as obesity. Incidence of these "modern" diseases is increasing worldwide.
Reduced Energy Expenditure - A Possible Root Cause
People who eat more calories need to burn more calories, otherwise their calorie surplus is stored as fat. For example, if we eat 100 more food calories a day than we burn, we gain about 1 pound in a month. Thats about 10 pounds in a year. Over two decades this energy surplus causes a weight gain of 200 pounds!
Assessing the contribution of lack of exercise to obesity is hampered by lack of research. According to existing surveys, only 20 percent of the population are frequent exercisers. In addition, only a small minority of children (1 in 5) regularly participate in after-school sports or extra-curricular physical activity. Since 1990, among adults there has been a per capita decline of 15 percent in frequent exercise activity (100+ days per year in any one activity). Among teenagers and adolescents aged 12-17, the plunge is 41 percent.
However, data on correlation between BMI and exercise frequency is almost non-existent, so we are unable to say exactly what effect lack of exercise has on obesity. What we do know is that severe clinical obesity leads to serious mobility problems caused by respiratory and musculoskeletal disorders. Thus the fitness capacity of obese individuals, especially those suffering from morbid obesity, is typically diminished.
Family Influence - A Major Contributory Cause to Obesity
Parental behavioral patterns concerning shopping, cooking, eating and exercise, have an important influence on a child's energy balance and ultimately their weight. Thus family diet and lifestyle are important contributory causes to modern child obesity, especially at a time of rising affluence. Since obese children and adolescents frequently grow up to become obese adults, it's clear that family influence also extends to adult obesity.
Genetic Causes of Modern Obesity
Genes affect a number of weight-related processes in the body, such as metabolic rate, blood glucose metabolism, fat-storage, hormones, to name but a few. Also, some studies of adopted children indicate that adopted children tend to develop weight problems similar to their biological, rather than adoptive, parents.
In addition, infants born to overweight mothers have been found to be less active and to gain more weight by the age of three months when compared with infants of normal weight mothers, suggesting a possible inborn drive to conserve energy.
Research has also shown that normal-weight children of obese parents may have a lower metabolic rate than normal-weight children of non-obese parents, which can lead to weight problems in adulthood. All of this suggests that a predisposition to obesity can be inherited.
However, the fact that obesity has increased so much in the last few decades appears to discount genetics as the main cause. According to Stephen O'Rahilly, professor of clinical biochemistry and medicine at Cambridge University, the influence of genetics on modern levels of obesity is insignificant:
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