Other Causes Of Obesity - Why People Become Overweight: Obesity
Content provided by the Faculty of the Harvard Medical School
Other causes of obesity
Clearly, our responses to today's obesity-promoting environment, in tandem with genetic influences, are the most significant causes of overweight and obesity. But in some people, drug side effects, illnesses, and genetic disorders can also play a role.
Drug side effects
Several prescription drugs can cause weight gain as a side effect by increasing appetite or slowing metabolism. These include corticosteroids such as hydrocortisone (used for a variety of conditions to reduce inflammation); estrogen and progesterone (used in oral contraceptives); anticonvulsants such as valproic acid (Depakote, others); certain anticancer medications; and drugs such as olanzapine (Zyprexa), haloperidol (Haldol), lithium (Eskalith, Lithobid), and clozapine (Clozaril), which are used to treat psychiatric conditions.
Paradoxically, weight gain can also be a side effect of some drugs used to treat conditions that result from obesity itself. Among these drugs are insulin and glyburide (DiaBeta and others); these are treatments for diabetes, which is common among people with weight disorders. Several antidepressants may cause patients to put on weight, including tricyclic antidepressants such as imipramine (Tofranil) or desipramine (Norpramin, Pertofrane), monoamine oxidase inhibitors (MAOIs), and selective serotonin reuptake inhibitors (SSRIs) such as paroxetine (Paxil), citalopram (Celexa), escitalopram (Lexapro), sertraline (Zoloft), fluvoxamine (Luvox), and fluoxetine (Prozac).
When used to treat depression, SSRIs may cause weight loss initially, but within six months of treatment they can induce weight gain in a significant number of patients. On the other hand, sibutramine (Meridia), another drug that stimulates serotonin (like the SSRIs), is an appetite suppressant that's used to promote weight loss. And in a small number of patients, SSRIs such as Prozac actually cause weight loss, making them useful as a therapy for weight disorders. Much more needs to be learned in this area; the relationship between weight regulation and serotonin (a key chemical communicator in the brain and elsewhere in the body) is obviously complex.
Illnesses that affect weight
A few illnesses that are characterized by an imbalance or an abnormality in your endocrine glands can also affect your weight. These include hypothyroidism (an underactive thyroid), polycystic ovarian syndrome, and certain unusual tumors of the pituitary gland, adrenal glands, or the pancreas. However, in the vast majority of people, these illnesses are not responsible for weight gain. Most are extremely rare. Hypothyroidism, which is the most common, is seldom the main reason for overweight or obesity. Treatment with thyroid hormone, while medically necessary, does not usually cause a significant weight reduction.
Genetic disorders
Obesity is also a symptom of some rare and complex disorders caused by genetic defects. These obesity syndromes usually appear in early childhood and are tied to several additional medical problems. One such disorder is Prader-Willi syndrome, a form of obesity associated with mild mental retardation that occurs in about 1 in 25,000 people and has been traced to abnormalities in a group of genes on chromosome 15. People with this disorder are unusually short and have primarily upper-body obesity. A less common disorder, Bardet-Biedl syndrome, is similar to Prader-Willi syndrome, but is caused by abnormalities in different genes. Several other rare genetic syndromes cause obesity, but account for only a tiny fraction of all weight disorders.
The trouble with TV: Sedentary snackingThe average American watches about four hours of television per day, a habit that's been linked to overweight or obesity in a number of studies. Data from the National Health and Nutrition Examination Survey, a long-term study monitoring the health of American adults, revealed that people with overweight and obesity spend more time watching television and playing video games than people of normal weight. Watching television more than two hours a day also raises the risk of overweight in children, even in those as young as three years old. Part of the problem may be that people are watching television instead of exercising or doing other activities that burn more calories (watching TV burns only slightly more calories than sleeping, and less than other sedentary pursuits such as sewing or reading). But food advertisements also may play a significant role. The average hour-long TV show features about 11 food and beverage commercials, which encourage people to eat. And studies show that eating food in front of the TV stimulates people to eat more calories, and particularly more calories from fat. In fact, a study that limited the amount of TV kids watched demonstrated that this practice helped them lose weight — but not because they became more active when they weren't watching TV. The difference was that the children ate more snacks when they were watching television than when doing other activities, even sedentary ones. |
| Last updated: | June 20, 2007 |
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Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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