Obesity

Obesity is defined as an accumulation of excess fat on the body. Foods provide nutrients and the calories we need for energy. Eating too much, however, leads to fat being stored in the body. Overeating regularly causes weight gain, and eventually obesity.

Obesity is considered a chronic (long-term) disease, like high blood pressure or diabetes. It has many serious long-term consequences for health, and it is the second leading cause of preventable deaths in the United States (tobacco is the first).

Women normally have more body fat than men, but an excess of 30% body fat in women or 25% in men is considered obese.

Obesity is often measured with a calculation called the body mass index (BMI). A BMI between 25 and 30 is usually considered overweight, and a BMI greater than or equal to 30 is considered obese. BMI greater or equal to 40 is considered morbidly obese. However, the figures above apply only to peoples of European ethnicity.

Obesity is an epidemic in the United States and in other developed countries. More than half of Americans are overweight—including at least one in five children. Nearly one third are obese. Obesity is on the rise in developing societies because food is abundant and physical activity is optional.

Each year, Americans spend billions of dollars on dieting, diet foods, diet books, diet pills, and the like. Another $45 billion is spent on treating the diseases associated with obesity. Furthermore, businesses suffer an estimated $20 billion loss in productivity each year from absence due to illness caused by obesity. The cost of obesity is high and getting higher.

Types
Obesity can be classified by its severity and by the way fat is distributed on the body. Both of these classifications are meaningful for predicting comorbidities (related health problems).

Severity
The severity and health risks of obesity vary with the body mass index, or BMI. The BMI is the person's weight in kilograms divided by their height in meters. The World_Health_Organization|World Health Organization (WHO) classifies obesity and health risk this way:
 * BMI less than 18.50 is underweight
 * BMI of 18.50–24.99 is normal weight
 * BMI of 25.00–29.99 is overweight, preobese, and at increased risk of cormorbities
 * BMI of 30.00-34.99 is overweight, obese, and at moderate risk of comorbidities
 * BMI of 30.00–39.9 is overweight, obese, and at severe risk of cormorbidities
 * BMI of 40.00 or higher is overweight, obese, and at very severe risk of comorbidities

Distribution of fat
Obesity usually occurs in one of two different body-fat distributions. The distinction between the two is important because one type is linked to more health problems.
 * "Pear" shape, or gynoid obesity: Most obese women follow this pattern, in which body fat is mostly distributed on the hips and buttocks.
 * "Apple" shape, or android obesity: This shape is more common in men, who tend to put on weight around their bellies. People with this type of fat distribution--women with waists greater than 35 inches or men greater than 40 inches--are more likely to develop health problems related to their obesity. The waist should be measured at the smallest spot under the rib cage, above the belly button.

Obesity occurs in both children and adults. In fact, childhood obesity in developed countries is being recognized as an increasingly common affliction.

Causes
Obesity happens when a person eats an excess of food relative to the energy they expend. Food is the body's energy source, and, once eaten, it is either stored or used to power the body's metabolism. However, the ways in which factors like appetite, food quality and quantity, energy storage, and energy use interact with each other are complex.

Genetics
Obesity tends to run in families. Also, some genetic disorders like the rare Prader-Willi syndrome can lead to obesity.

Environment
Environment plays a tremendous role in determining whether people become obese. High-calorie food that is easily available can tempt people to eat without thinking about nutrition. A box of doughnuts at the office is hard to pass up. People living in neighborhoods without sidewalks do not as easily incorporate simple exercise into their day. The more they drive rather than walk or jog, the less exercise they get. People too busy to cook may buy unhealthy restaurant food. They may not get enough sleep, which can lead to weight gain.

Poverty has been linked to obesity. There are probably many reasons for this, such as the fact that in poor neighborhoods it is easier and less expensive to buy fast food than fresh produce. It may be harder to get to a gym, and it may not be safe to walk around.

Other causes
Some cases of excess weight gain are caused by other illnesses, medications, or miscellaneous factors.
 * Hypothyroidism is a condition in which the thyroid gland of the neck does not produce enough thyroid hormone. This affects how the body uses energy, leading to increased storage of energy and less spending of energy. In other words, the rate of metabolism is slowed down.
 * Cushing's syndrome is a condition in which the body is exposed to an excess of the hormone cortisol, either from an abnormality of hormone secretion in the body or from taking steroids like prednisone for a long time. Body fat is distributed to the upper body, face, and neck in Cushing's syndrome, and the characteristic appearance is sometimes called "Cushingoid."
 * Prader-Willi syndrome is a rare inborn genetic disorder that includes problems with the hypothalamus, a part of the brain that controls hunger. People with Prader-Willi syndrome feel constantly hungry and are compulsively driven to overeat.
 * Medications like steroids, some antidepressants, and some psychiatric or antiseizure medications can cause changes in energy storage or the body's tendency to hold on to water. This may lead to overweight or to obesity.

From nightly sleep to genes, Dr. Marc Bessler, an obesity expert at New York-Presbyterian Hospital, explains the factors that lead to obesity in the following video from BigThink:

Diagnosis
Obesity can often be diagnosed visually, but in order to classify it and predict the likelihood of comorbidities, it is helpful to calculate a body mass index (BMI), use weight-for-height tables, or directly measure body fat.

Body mass index (BMI)
BMI is a number. It is a person's weight divided by his height, using kilograms and meters as the measurement units. Health care providers use the BMI to determine a person’s weight status. They also look at BMI, along with information about additional risk factors, to determine a person’s risk for developing obesity-related diseases.

The BMI is helpful in many respects. It is more accurate than a person's weight in determining if they're obese or overweight. It is a simple calculation to make, it changes as the person's weight changes, and is an easy number to work with in research studies that need to categorize large numbers of people who are obese to varying degrees.


 * Adult BMI calculator

In adults:

For children ages two and older, and for teens, BMI adds sex and age into the calculation. Instead of using a specific number like adults do, the BMI for children and teens listed as a percent. This percent indicates a child’s BMI in relation to the BMIs of other children the same sex and age. It is called a percentile.
 * A BMI between 18 and 24.9 is considered to be a healthy weight.
 * A BMI of 25 to 29.9 is considered overweight.
 * A BMI of 30 or above is considered obese.


 * Child and Teen BMI Calculator



Children ages two and older are considered:


 * At a healthy weight if their BMI falls between the 5th and the 85th percentiles.
 * At risk for being overweight if their BMI is in the 85th to 95th percentile.
 * Overweight or obese if their BMI is at or higher than the 95th percentile.

BMI is not a perfect measurement, though, and isn't always accurate. The use of the BMI to determine obesity has been criticized by researchers who find that some obese people, who have measurable excess fat, are not considered obese if just the BMI is used. Most of these people fall into the intermediate BMI range. In such cases the BMI is misleading.

Weight-for-height tables
An actuarial standby, weight-for-height tables give a range of weights expected for men or women of specific heights. Sometimes body frame types are taken into account. These charts may be good rough guides but are not always accurate. For example, muscular people like athletes can weigh more than the expected weight and not be obese.

Measuring body fat
Since obesity is defined as an excess of body fat, measuring body fat is the most accurate and direct way to determine if someone is overweight or obese, and to what degree. Techniques for doing this include:


 * Dual energy absorptiometry (DEXA) scan: This is a low-energy type of X-ray that is usually used to measure bone density but which can give information about body fat as well. It is very accurate.
 * Skinfold calipers: These pincer-like devices measure the thickness of skin folds and the fat beneath them at several sites on the body. The readings are used to determine body fat percentage.  It is inexpensive and relatively accurate if it is done by experienced practitioners.
 * Hydrostatic weighing: Also known as hydrodensitometry, this is a technique for weighing a person while they are underwater. It is quite accurate, but unwieldy and expensive.
 * Bioelectric impedance: This technology can be found in body-fat scales that can be used at home. This technique is less accurate because it depends in part on the amount of water present in the body, food intake, and skin temperature, all of which vary from one time to another.

Treatment
The goals of treatment for obesity is to reduce body fat and thereby reduce the accompanying health risks. Bariatrics is a specialty of medicine that treats obesity.

Diet
A healthy diet refers to the foods one eats on a regular basis, not a set of changes adopted for a few weeks at a time. Nutritionists agree that "dieting," per se, does not work, and that any healthy food habits one adopts need to be permanent.

Public health organizations in the United States have periodically made certain dietary recommendations. In the 1980s it was thought that a low-fat diet was the best way to control one's weight. However, often when people reduce the fat in their diet, they substitute high-calorie snacks loaded with sugar or other simple carbohydrates, and the high glycemic index of these foods contributes to excess weight. The glycemic index is a measure of how easily digested a starchy food is, and how high a person's blood sugar rises after eating it. High glycemic-index foods are very easily digested and cause an abrupt rise in blood sugar, which in turn causes a rise in the body's secretion of insulin. It is important to understand, however, that the glycemic index of food is affected by the amount of protein ingested with the food in question. The glycemic response of food is decreased if ingested with protein. Research has shown that insulin stimulates fat storage and weight gain. Insulin is the primary regulator of fat storage and the higher your insulin levels, the more fat you will store.

In addition, because high glycemic-index foods are digested so quickly, a person quickly becomes hungry and craves more carbohydrates. This leads to excessive eating. Therefore, many experts recommend a low-carbohydrate diet, or more properly a low-glycemic index diet, for weight loss and weight control. This diet is based on avoiding foods high in starches and sugars, including of course fructose. This would include eliminating or limiting (or substituting full-grain varieties) of foods like pasta, cereals, breads and breaded foods, rice, white potatoes, and sugars.

Exercise
Getting enough physical activity is one way to help prevent or reduce overweight and obesity-related health problems.

On September 5, 2002, the US Institute of Medicine recommended that children and teens as well as adults get 60 minutes of physical activity on five or more days a week to be healthy. It also released a series of revised dietary recommendations.

A study of people ages 50-71 who exercised at least 30 minutes a day on most days of the week found a substantial decrease in mortality rates compared with people who didn't. The authors thought it likely that even smaller amounts of exercise could be beneficial.

Surgery
Bariatric surgery is a weight-loss option for people with severe obesity, usually those with a BMI greater than 40, or greater than 35 with at least one severe obesity-related medical problem. It tends to be a last resort after exercising, dietary changes and medications have failed, because like any surgery it can have complications.



There are several types of bariatric surgery. Gastric banding is a procedure that places a band around the opening of the esophagus just where it meets the stomach. The tighter the band, the less food a person feels comfortable eating. The band may be adjusted through a port in the skin. Gastric bypass surgery, also known as Roux-en-Y (roo-on-WHY), reduces the size of the stomach to an egg-sized pouch, then attaches that pouch to a downstream part of the intestine, bypassing two feet of intestine.

Bariatric surgery is a risky procedure and patients frequently suffer complications. Long-term follow-up care is a must, as is lifelong vitamin supplementation. For some morbidly obese people, though, the benefits of weight loss outweigh the risks of bariatric surgery.

Videos: Weight Management Surgery
In this video from BigThink, Dr. Marc Bessler, obesity expert at New York-Presbyterian Hospital, says expected procedures, such as a stomach balloon, will transform the field in the next few years:

Dr. Bessler also describes obesity as a disease, lists the best hospitals for surgery, and gives advice on how to afford the procedure, in this additional BigThink video:

In yet another BigThink video about weight management surgery, Dr. Bessler explains when it is advisable for obese patients to undergo surgery:

Other treatments
Vagal nerve stimulation is an experimental procedure that is already used to treat severe epilepsy and major depression, and is being studied in rats to reduce appetite.

Medications
There are two main types of effective weight-loss medications.


 * Appetite suppressants: These work by increasing levels of brain chemicals like serotonin or norepinephrine. Examples include sibutramine (Meridia) and phentermine (Adipex-P, Ionamin, Fastin). All of these drugs are controlled substances, which means that physicians must be specially privileged to prescribe them.
 * Lipase disruptors: Orlistat (Xenical) is the only drug of this type. It works by preventing the body's normal breakdown of fats so that some of the fat passes through the intestine without being absorbed. This means that fewer of the calories that are eaten get absorbed.

These drugs are more effective in people who make dietary changes and exercise more than in people who just take the drugs. They tend not to be effective for more than a few months at a time. As with almost all medications, weight-loss drugs have side effects and are not safe for everyone.

Several drug and drug combinations are in study for helping weight loss. These include rimonabant, bupropion in combination with other medicines,topiramate, exenatide, lorcaserin, and tesofensine, just to name a few.

Supplements
Obesity is a common problem that isn't easy to treat, which means there is an enormous market for quick fixes. Thousands of supplements and other treatments are sold over the counter or through catalogs that promise weight loss. Much of this is quackery. The fact is that no safe supplement causes weight loss unless the person taking it is also changing his diet and exercise habits for the better.


 * Ephedrine (ephedra, ma-huang): The US Food and Drug Administration (FDA) on April 12, 2004, prohibited dietary supplements containing ephedra.

Prevention
It's easier to prevent obesity than to cure it.

In addition to a healthy lifestyle, people can help prevent overweight and obesity by balancing a healthy diet with enough physical activity. It is important to create balance between the food eaten (Energy IN) and physical activity (Energy OUT).

There are also some simple steps people can take that can affect their weight and health over the long term. For example, cutting out one soda a day, or taking the stairs instead of the elevator are small changes that can make a big difference in health over time.

Preventing overweight and obesity, especially in children, goes beyond just eating a healthy diet and getting enough physical activity. It may be more helpful to think about adopting a “healthy lifestyle”.

A healthy lifestyle could include:


 * Eating a healthy diet
 * Getting enough physical activity
 * Maintaining a healthy weight
 * Reducing “screen time”—time spent watching TV, playing video games, or on the computer
 * Limiting or eliminating tobacco, drug, and alcohol use
 * Reducing stress
 * Having a health care provider, scheduling and keeping regular visits, and taking medications correctly

Adopting a healthy lifestyle involves individuals, families, neighborhoods, and communities. This type of lifestyle can make it more likely for people to stay healthy, including controlling their weight and preventing obesity.

A healthy diet:


 * Emphasizes fruits, vegetables, whole grains, and fat-free or low-fat milk and dairy products.
 * Includes lean meats, poultry, fish, beans, eggs, and nuts.
 * Is low in saturated fats, trans fats, cholesterol, salt (sodium), and added sugars, and high-starch foods. Saturated fats, trans fats, and cholesterol tend to raise “bad” (LDL) cholesterol levels in the blood, which in turn increases the risk for heart disease.

Achieving and maintaining a healthy weight is about FINDING A BALANCE through healthy eating and physical activity.

Related Problems
Unfortunately, obesity is not just a problem of appearance. It can worsen, or lead to, a great many other health problems, ranging from minor nuisances like fungal skin infections to life-threatening ones like stroke.

Common major diseases that have been linked to obesity include:


 * Heart disease
 * Type 2 diabetes
 * High blood pressure
 * Cancer

The following is a list of diseases, organized by body system, that can be caused or worsened by, or are commonly associated with, obesity.


 * Cardiovascular: Hyperlipidemia, hypercholesterolemia, hypertension, venous stasis disease, atherosclerosis, coronary artery disease, stroke
 * Endocrine: Metabolic syndrome, diabetes mellitus type 2
 * Respiratory: Obstructive sleep apnea, asthma, obesity-hypoventilation syndrome
 * Dermatologic: fungal skin infections, acanthosis nigricans
 * Nervous: Migraine, pseudotumor cerebri
 * Gastrointestinal: Gallbladder disease and gallstones; fatty liver disease (nonalcoholic steatohepatitis or NASH; gastroesophageal reflux disease (GERD), colon cancer, esophageal cancer
 * Reproductive: Polycystic ovarian syndrome, breast cancer, endometrial cancer
 * Urologic: stress incontinence, renal cancer
 * Musculoskeletal: Osteoarthritis, degenerative joint disease, gout, decreased muscle mass

For children, overweight also increases their health risks. Type 2 diabetes was once rare in children, but now it accounts for 8 to 45% of newly diagnosed diabetes cases in American children and teens. Overweight children are more likely to remain overweight or become obese as adults.

Controversy
Obesity is one of the most controversial subjects in health research. There are many hypotheses about what causes obesity, and many proposed ways to treat it. When a condition is this controversial, it is always helpful to examine research studies that carefully gather evidence, rather than relying on personal stories or anecdotes, in order to determine which information is most useful.

Recent and ongoing controversies include:
 * Whether any medication is best to treat obesity.
 * Whether other treatments like surgery or vagal-nerve stimulation are safe and effective enough to be widely adopted.
 * To what degree the health risks attributed to obesity are really due to yo-yo dieting.
 * Whether obesity can be "spread" from person to person, like a virus.
 * Whether obesity is really such a risk to health. Can a person be both obese and healthy?
 * Whether public-health measures like a tax on unhealthy foods would be helpful to curb obesity in the general public.
 * Whether low-carbohydrate diets prevent or treat obesity.

Epidemiology
Before the 20th century, obesity was rare; in 1997 the WHO formally recognized obesity as a global epidemic. As of 2005 the WHO estimates that at least 400 million adults (9.8%) are obese, with higher rates among women than men. The rate of obesity also increases with age at least up to 50 or 60 years old and severe obesity in the United States, Australia, and Canada is increasing faster than the overall rate of obesity. Once considered a problem only of high-income countries, obesity rates are rising worldwide. These increases have been felt most dramatically in urban settings. The only remaining region of the world where obesity is not common is sub-Saharan Africa.

The United States faces a very serious public health crisis of overweight and obesity. In 2001, 64.6% of American adults were overweight or obese. Children are getting heavier as well. The percentage of children and teens that are overweight has more than doubled in the past 30 years. Today, about 17% of American children ages 2-19 are overweight.

Obesity became an epidemic in about 1980, and since then has been on the rise in countries around the world. A 2007 study of patients in 63 countries around the world found that an astonishing 64% of men and 57% of women were either overweight (BMI 25-30) or frankly obese (BMI greater than or equal to 30). Overweight women now exceed underweight ones in many developing countries.

In the following video from BigThink, Barry Bloom, Professor of Public Health at Harvard University, provides a visual presentation of the surge in American obesity. Though the 'disease' is communicated culturally, the Professor of Public Health at Harvard argues that it should still be considered the world's next major medical epidemic:

Social Issues
Obesity can be socially devastating. Obese people sometimes face contempt and discrimination from others, and they can suffer from problems of self-image.

Obese people are often falsely perceived as gluttonous or lazy. Organizations like the National Association to Advance Fat Acceptance are working to change this perception.

Public Health
Obesity has been on the rise for several decades, although dietary fat has fallen and caloric intake for most pediatric groups, at least in the US, has been steady. Simple carbohydrate intake may be to blame, particularly in children, who regularly consume fruit juices and snacks like potato chips.

Public Health and Policy
The World Health Organization formally recognized a worldwide obesity epidemic in 1997, almost 20 years after it had begun.