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Causes of Obesity and Overweight
Genetic and Environmental Reasons for Weight Gain
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Causes of Obesity

Short Articles About Obesity and Overweight
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Does Obesity Increase the Risk of Premature Death - Syndrome X & Obesity
Rise of Obesity and Diabetes - Does Overweight Shorten Life? - Obesity & Risk of Premature Death
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Obesity Health Dangers for Children - Obesity & Colon Cancer - Health vs. Weight Loss
Body Fat & Cancer - Obesity, Weight Loss & Immune Function - Weight Loss & Sleep Apnea
Glycemic Index & Obesity - Health, Weight & Obesity

Weight gain occurs when a person consumes more calories than he or she burns. A minor calorie surplus leads to overweight, while a major energy surplus causes obesity. But what causes this imbalance between calories in and calories in the first place may differ from one person to another. Genetic, environmental, psychological, and other factors all play a part. Here are some of the more common causes of obesity.

Causes of Obesity - Genetics

Obesity tends to run in families, implying genetic factors. The search for an "obesity gene" is complicated, however, by the fact that families also tend to share eating and lifestyle habits, making it difficult to separate genetics per se from behavior.

Studies have been designed to determine how significantly genes and family lifestyles affect obesity. Some studies of adopted children indicate that genetics and heredity do play some role.

Adopted children tend to develop weight problems similar to their biological, rather than adoptive, parents.

But although children of obese parents have a 25-30 percent extra likelihood of becoming obese themselves, part of this increased risk of obesity may be due to eating habits and poor family nutrition, rather than heredity.

Causes of Obesity - Genetic Predisposition to be Overweight Rather than Obese

Many studies have found a genetic link to obesity, showing that the pattern of deposition of fat - i.e. the way fat builds up around the body - and the degree of overweight can both be inherited.

Body shape, for example, generally falls into one of three categories - ectomorph, endomorph or mesomorph. The slighter frames of ectomorphs reflect a low capacity for fat storage. Endomorphs have the most fat-storage capacity. And mesomorphs have an ability to store fat that falls somewhere in between. Fat storage is also more evenly distributed. These are stereotype body shapes. In practice, most people are a combination of all three, with a disposition to be more like one or two of them. It is doubtful whether a person's body shape and fat distribution is sufficient to cause obesity.

Causes of Obesity - Genes - Body Shape

Other research has shown that often normal-weight children of obese parents have a lower metabolic rate (they tend to burn more calories than average even when they're asleep, or else they burn fewer calories for the same physical activity) than normal-weight children of non-obese parents. Again, this suggests that the susceptibility to obesity can also be inherited. But the fact that obesity has increased so much in the last few decades appears to discount genetics as the main cause.

Causes of Obesity - Genetics - Leptin

In her book, The Hungry Gene, Ellen Shell promoted the idea that leptin - a naturally occuring hormone that controls the appetite - may be one of the causes of obesity. When full, fat cells release the hormone leptin, which curbs appetite. If leptin production is hindered, the fat cells are unable to signal that they're full, and weight gain occurs. Research into leptin is only just beginning, although the leptin-obesity link appears to have been disproved by some initial studies.

Causes of Obesity - Genes - Hormones

A small minority of cases of obesity can be explained by glandular or hormonal problems. One such problem is clinical hypothyroidism, where there is not enough thyroid hormone to control normal rates of metabolism. Also, Cushing's Syndrome, where the production of the corticosteroid hormones is abnormal.

Sex hormones can also affect obesity. In women, body fat levels during adolescence, pregnancy and the menopause are determined by the balance of female sex hormones. Changes in energy intake, desire for food and specific cravings occur at various stages of the menstrual cycle. Some women appear to be more susceptible than others to hormonal changes and many overweight women cite pregnancy as the time when their problem started.

Causes of Obesity - Genetics - Summary

Genetics and weight (and thus obesity) are inextricably linked. The question is, to what extent can the explosion of overweight and the modern levels of obesity be attributed to genes? 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:

"Nothing genetic explains the rise in obesity. We can't change our genes over 30 years."

Causes of Obesity - Gender

Weight is affected by gender. Men have more lean body mass (muscle) and less fat than women. Lean body mass is more metabolically active and thus uses more energy (calories) than fat. So even at rest, men burn between 10 and 20 percent more calories than women. However, while women are more predisposed to gaining weight than men, this gender-induced susceptibility to gain weight cannot account for the obesity problem.

Causes of Obesity - Environmental factors

Environment also strongly influences obesity. An environment where people eat high fat and high sugar diets and take little exercise, causes more problems with excess weight and obesity than one where people eat low fat diets and get regular exercise. Americans live in an environment that marginalizes the obese while simultaneously creating the perfect environment for weight gain as a result of it's fast-food and convenience-food culture. Also, due to it's culture of convenience, TV and labor-saving devices, most Americans do not get enough physical activity which is another prime environmental cause of obesity and weight gain.

Causes of Obesity - Psychological Factors

  • Psychological factors may also influence eating habits. A number of psychological factors and behavioral problems may cause people to gain weight. Many people over eat when they're stressed, bored or angry. Over time, the association between an emotion and food can become firmly fixed.

  • Although research indicates that most overweight people have no more psychological problems than people of average weight, it is estimated that up to 10 percent of people who are mildly obese and try to lose weight repetitively have binge eating disorder. During an episode of binge eating, people eat large quantities of food with no sense of self-control. Those with the most severe binge eating problems are also likely to have symptoms of depression and low self-esteem. These people have more difficulty losing weight and keeping it off than people without binge eating problems.This disorder is even more common in people who are severely obese.

  • Depression and stress can lead to obesity. They are leading causes of eating disorders. Indeed, most eating disorders can be traced to behavioral or psychological difficulties. Even lack of confidence can lead to social withdrawal and a sedentary-type lifestyle that promotes weight gain and ultimately obesity.

Causes of Obesity - Illness and/or Drugs

Some illnesses can lead to obesity or a tendency to gain weight. These include hypothyroidism, Cushing's syndrome, depression, and certain neurological problems that can lead to overeating. Also, drugs such as steroids and some antidepressants may cause weight gain. A doctor can tell whether there are underlying medical conditions that are causing weight gain or making weight loss difficult.

Causes of Obesity - Lack of Physical Activity

As stated above, weight gain occurs when a person consumes more calories than he or she burns. So far we have dealt with an excess of energy/calories IN. But lack of calories OUT is also one of the major causes of weight gain and obesity. Lack of physical activity caused in part by watching too much TV, or playing too many computer games is strongly associated with obesity levels, especially in young people.

Causes of Obesity - Summary

Obesity is a complex issue and a serious illness rather than simply a weight condition. The causes of obesity are various and often interlinked - one reason that weight loss drugs or simple dieting, by themselves, are usually inadequate to treat those suffering from obesity. Typically, obesity treatment involves a combination of diet, exercise, medication and counseling. Even then, long term results of such obesity treatment are mixed.

If You Suffer from Obesity - the First Step

If you suffer from obesity, your first step should be to seek professional help.


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