Topic: Body Composition/Weight Management



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Causes of Obesity

As discussed in the first reading section, the term "overweight" is not very descriptive, simply referring to the state of having higher-than-average body mass. The body can be very muscular and have a low fat percentage, but still be termed "overweight" according to an average height-and-weight chart, because muscle weighs more than fat. The term "overweight" is used by many to mean something else, usually "overfat," or "obese." An "obese" individual has excessive fat on his/her body. Knowledge of whether one is overfat, or obese, is important because obesity may lead to a variety of other health problems, including heart disease, stroke, diabetes, kidney stones, gallstones, some forms of cancer and osteoarthritis.

While most health promoters advocate for reducing obesity, the fact so many people suffer from the condition can make this task difficult across any population. Briefly described below are several contributing causes to obesity.


A high-fat diet can certainly contribute to an increased risk for obesity. In fact, the body notoriously becomes more efficient at meeting challenges. The body may, in a high-fat diet, learn to store fat more easily--which would increase one's body fat percentage.

Fast food

This photo, originally taken by Christian Cable, is in the public domain, retrieved from Wikimedia Commons


It is well established through "twin studies" research that genetics plays a role in obesity. Identical twins, who have the same genetic makeup, are more likely to be obese than are fraternal twins. More and more is being uncovered regarding the genetic link to obesity as time passes. Several of the "obesity causes" listed as stand-alone contributors to the condition may have genetic links. For example, there appears to be a genetic link to one's metabolic rate and obesity.

Genetics may play a role in specific conditions, such as Prader-Willi syndrome (see below photo), a rare disorder featuring a variety of symptoms, including obesity.

A photograph of an individual with Prader-Willi Syndrome.

The above photo, taken in Turkey by Navit Dilmen, is in the public domain, available via Wikimedia Commons.

Metabolic Rate

Metabolism refers to the sum of all chemical reactions occurring in the body. On a more general level, one can think of the balance between the energy we put into our bodies through food versus the energy we give off through sleep, rest, temperature change, digestion, exercise and other activities. A person who expends a lot of energy is said to have a "high metabolic rate" ( keep in mind this is a very simplified application to a complex concept). Metabolism is higher during periods of growth, pregnancy and physical activity. An individual with a 'high metabolic rate' is less likely to be obese than a person with a "low metabolic rate." Since nicotine, a stimulant, tends to increase metabolic rate, which is one reason why many users continue to smoke.

Research on "brown fat" versus "white fat," and their effects on metabolism, has been publicized in the media. Barbara Moran, in a June 2014 Boston University Today article (R), for example, provides information on how the presence of "brown fat" in adults--previously thought to be non-existent--is indeed present and may impact an individual's metabolic rate.

Lipoprotein Lipase Activity

Lipoprotein lipase is an enzyme that can trigger triglycerides (the fat most commonly consumed in a typical diet) to release fatty acids into muscle or fat cells, causing fat deposition i.e. the cells become fatter. Therefore, an individual with elevated lipoprotein lipase activity is more likely to be obese than an individual with lower lipoprotein lipase activity.

Hormonal Disorders

Metabolic, or hormonal, disorders that have a link to obesity include autoimmune thyroid disease, polycystic ovarian syndrome, and Cushing's syndrome.

Autoimmune Thyroid Disease
The thyroid is a butterfly-shaped gland located in the front of the neck. The thyroid, involved with many body functions including metabolism, releases several hormones, two of which are known as "T4" and "T3." T4 and T3 (T3 being the 'active' form of T4) function to help the body convert oxygen and calories from food into energy. The release of these hormones occurs from a feedback mechanism. A hormone, TRH, is released from the brain's hypothalamus. The release of TRH  (thyrotropin releasing hormone), in turn, causes the release of TSH (thyroid stimulating hormone) from the pituitary gland. The amount of TSH circulating in the blood tells the thyroid how much T3 and T4 to release. View a 1.5-minute video clip through about thyroid disease (R).

In autoimmune thyroid disease, antibodies attack the thyroid, causing damage to the gland. The damage usually results in a reduction of thyroid hormone released, or hypothyroidism. The brain tries to increase the amount of thyroid hormone by releasing more TSH, but the damaged thyroid is unable to respond. A person whose blood tests show low levels of T4 and T3 and high levels of TSH may be considered "hypothyroid." This hypothyroidism condition, the result of antibodies attacking the thyroid gland, is termed Hashimoto's Thyroiditis, or Hashimoto's Disease. Symptoms of Hashimoto's Disease are many and can include weight gain, changes in blood pressure, heart palpitations, anxiety, changes in mood, hair loss, lack of energy, exhaustion, sensitivity to heat or cold, muscle and joint pain, puffiness in the eyes or other facial features, low sex drive, and concentration problems. A person with Hashimoto's Disease may put on weight because of the low thyroid hormone levels in the body. The weight gain can be worsened by other symptoms, such as mood changes and the lack of energy. Individuals diagnosed with Hashimoto's Disease are typically put on thyroid hormone replacement therapy. Interestingly, however, diagnosis may not occur for many. Blood tests issues usually involve obtaining T4, T3 and TSH, but a person can have normal levels of these hormones and still have autoimmune thyroid disease. Therefore, a blood test for thyroid antibodies can better diagnose a patient suffering from the above symptoms. Once diagnosed, the Hashimoto's patient usually is prescribed thyroid hormone therapy. Symptoms may be alleviate for some, less so for others.

Grave's Disease is another autoimmune thyroid disease also caused by antibodies. The antibodies serve to increase the release of T4 and T3, causing another laundry list of symptoms, including unexplained weight loss, bulging of the eyes, hand tremor, restless leg syndrome, mental confusion, inability to sleep, dry skin, erratic behavior, sensitivity to heat or cold, high blood pressure, insomnia or difficulty remaining asleep, and muscle weakness in the upper arms and legs. Interestingly, the medical community currently treats Grave's Disease by reducing the activity of the thyroid via radioactive iodine treatment (RAI). RAI partially or fully disables the thyroid, so the body becomes hypothyroid. The patient then is prescribed thyroid hormone therapy. Some endocrinologists first try to treat the condition using antithyroid medications, hoping the Grave's Disease will go into remission. In severe cases, the entire thyroid is removed, rendering the patient hypothyroid.

Polycystic Ovarian Syndrome
In Polycystic Ovarian Syndrome, there is an excess of androgen ("male") hormones, and an imbalance of other hormones e.g. Follicle Stimulating Hormone, secreted by the pituitary gland. The hormonal imbalance may lead to irregular or stopped ovulation, enlarged ovaries with many cysts, excessive hair growth, and obesity. presents a profile of a woman diagnosed with Polycystic Ovarian Syndrome (O).

Cushing's Syndrome
Cushing's Syndrome is an uncommon condition resulting from the body's exposure to too much cortisol, a hormone produced by the adrenal glands. Since cortisol is a hormone secreted during times of stress, some individuals e.g. those with anxiety disorders, mood disorders, and those dealing with extraordinarily extreme distress may have higher levels than the average individual. Glucocorticoids, similar in structure to cortisol, are medications prescribed for certain conditions, such as asthma, lupus, and rheumatoid arthritis, and may also lead to a higher likelihood for Cushing's Syndrome. Other causes of Cushing's Syndrome include abnormal growths/tumors in the pituitary or adrenal glands. Signs and symptoms of Cushing's Syndrome include obesity; a round, moon-shaped face; fatigue; high levels of blood glucose; hypertension; a hump between the shoulders, in the upper back; and anxiety. NGC presents an interesting news special, via Youtube, profiling a young woman diagnosed with Cushing's Syndrome (O).

Set Point Theory

This theory stipulates the body has a predetermined weight it is most comfortable at--a "set point." The body will experience difficulty in deviating from this internally controlled set point, for either gaining or losing weight. In the January 2012 TIME Healthland article, Diet Disruptor: How the Brain Sabotages Weight Loss, research regarding brain changes to support a "set point" theory is described (O). While this controversial theory has had many strong proponents, there are also many detractors. In 2003, OB/GYN News published an article titled, "New Data Challenge Popular Set Point Theory of Obesity" (O).

Biochemical Theory

A more recent theory relates obesity to variations in specific brain chemicals. Brain chemicals called neurotransmitters are responsible for helping brain cells communicate. One brain cell (a brain cell is also known as a neuron) will deliver its message to an adjacent brain cell by releasing a neurotransmitter, a chemical meant to bind to specific receptors on the adjacent nerve cell. The binding of the neurotransmitter to the receptors will allow the message to continue from the first neuron to the adjacent one. Many researchers argue an imbalance of certain neurotransmitters in the brain, such as dopamine, serotonin and norepinephrine--only a few of the many neurotransmitters in the body--can trigger obesity. For example, Brookhaven National Laboratory released information on a link between dopamine and obesity in 2001 (O). Scienceline further describes how dopamine might come into play, using the American cultural holiday, Thanksgiving, in the example (O, 2009). A dopamine-deficient individual may experience depression, addictive tendencies, and sexual dysfunction. Medical News Today, in its article, Compulsive Eating That Leads to Obesity Has Similar Biology to Drug Addiction, describes research published in Nature Neuroscience that prompts a relationship among compulsive eating, drug addiction, and the brain (O).

 Researchers have also been studying the connection between serotonin and obesity, as described in Medical News Today (O, 2009). A serotonin-deficient individual may experience sugar cravings and other food-centered obsessions, anxiety and binge eating. 

Stephen M. Sahl, M.D., Ph.D., wrote an article available on the website, Neuropharmacology of Obesity: My Receptors Made Me Eat It (O).

Viral Infections

Whether obesity can be caused by a virus is a controversial topic. Dr. Nikhil Dhurandhar, while conducting research on Indian chickens killed by an adenovirus in the 1980s, noticed many of these chickens were large. His subsequent experimental research involved infecting animals with a recognized adenovirus known as Ad-36. The animals gained weight. Fox News provides an online story about the concept, including contributions from Dhurandhar (O). Pennington Biomedical Research Center, where Dhurandhar currently works, has released more information about obesity and Ad-36 in humans. In the study, the research team found 30% of screened obese individuals tested positive for Ad-36 antibodies, while only 11% of the slim individuals had the antibodies (O).

Fat Cell Theory

Rather well accepted, this theory stipulates a person can gain or lose weight through changes in fat cell number and size. To gain fat, the body can increase its number of fat cells ("hyperplasia"). The body can also gain fat by increasing the size of a fat cell ("hypertrophy"). Hyperplasia is thought to be particularly significant in child-onset obesity, whereas hypertrophy is thought to be particularly significant in adult-onset obesity. 

In order to lose fat, the body cannot get rid of the fat cells once they are formed; it can only decrease the size of those fat cells. The BBC News reports on some 2002 research investigating the possibility of controlling the development of fat cells. (O) describes research published in Nature in its article, Fat Cells Only Change in Volume, Not Number, and It's Determined in Teens (O).


Environmental "cues" can prompt an individual to eat. Examples of an environmental trigger is the person who eats when stressed, the person who snacks on high-fat foods when "The Late Show" airs on television.
Cultural influences can also shape eating behaviors. In the American Thanksgiving holiday, for example, heavy food consumption is not only common but almost positively reinforced. Similarly, on some religious holidays much attention is drawn to the meal table.
Photo of woman and child
This photo is in the public domain, originally retrieved via Wikimedia Commons.
Imitation can influence children who see their parents indulging in high-fat, large-serving meals. Incidentally, children with obese parents are more likely to be obese themselves.
Food is sometimes used as reinforcement. Examples of using food as reinforcement include: people rewarding themselves with "junk food" when spending extra time at work; rewarding a child with a treat for completing a chore, etc.


The amount of sleep an individual gets on a regular basis may also affect weight. The hormones ghrelin, leptin, and cortisol can shift when an individual does not receive enough sleep. This sleep-induced hormone shift may lead to weight gain. The below image shows a myriad of issues that may develop with sleep deprivation, including obesity.

Sleep Deprivation Effects

 The above image, created by Mikael Haggstrom, is in the public domain, available via Wikimedia Commons.

In 2013 the New York Times published an article written by Anahad O'Connor that describes how sleep deprivation, even in the short-term, may trigger an increased impulse to eat "junk food" (O).

With many possibilities and conditions to explain obesity, one can see why the condition is more than simply a need to exercise.

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Educational Enrichment

The Weight of the Nation - HBO film

A 2008 Newsweek article, Pleasure Factor, describes a research theory: some women may be genetically predisposed to enjoying eating less than others and may subsequently compensate by eating more

In August of 2003, there was some media attention about the relationship between obesity and urban sprawl (

Diet and Weight Loss with Thyroid Disease ( describes medications used to treat obesity

Contagious Obesity? Identifying the Human Adenoviruses that May Make Us Fat (Science Daiy, 2006)

Obesity Research at the National Institutes of Health

Obesity and Genetics (CDC)

Center for Metabolism and Obesity Research

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