FITNESS ARTICLES

To determine if someone is obese, doctors and other health care professionals often use a measurement called body mass index (BMI). First, a doctor measures a person's height and weight. Then the doctor uses these numbers to calculate another number, the BMI.

Once the doctor has calculated a person’s BMI, he or she will plot this number on a specific chart to see how it compares to other people of the same age and gender. A person with a BMI above the 95th percentile (meaning the BMI is greater than that of 95% of people of the same age and gender) is generally considered overweight. A person with a BMI between the 85th and 95th percentiles typically is considered at risk for overweight. Obesity is the term used for extreme overweight. There are some exceptions to this formula, though. For instance, someone who is very muscular (like a bodybuilder) may have a high BMI without being obese because the excess weight is from extra muscle, not fat.

People gain weight when the body takes in more calories than it burns off. Those extra calories are stored as fat. The amount of weight gain that leads to obesity doesn't happen in a few weeks or months. Because being obese is more than just being a few pounds overweight, people who are obese have usually been getting more calories than they need for years.

The number of people who are obese is rising.
About 1.2 billion people in the world are overweight and at least 300 million of them are obese, even though obesity is one of the 10 most preventable health risks, according to the World Health Organization. In the United States, more than 97 million adults - that's more than half - are overweight and almost one in five adults is obese. Among teenagers and kids 6 years and older, more than 15% are overweight - that's more than three times the number of young people who were overweight in the 1970s. At least 300,000 deaths every year in the United States can be linked to obesity.

In the United States, women are slightly more at risk for becoming obese than men. Race and ethnicity also can be factors - in adolescents, obesity is more common among Mexican Americans and African Americans.

Although there are genetic and hormonal influences on body weight, ultimately excess weight is a result of an imbalance of calories consumed versus calories burned through physical activity. If you consume more calories than you expend through exercise and daily activities, you gain weight. Your body stores calories that you don't need for energy as fat.

The following factors — usually working in combination — can contribute to weight gain and obesity.

Diet.
Regular consumption of high-calorie foods, such as fast foods, or increasing their portion sizes contributes to weight gain. High-fat foods are dense in calories. Loading up on soft drinks, candy and desserts also promotes weight gain. Foods and beverages like these are high in sugar and calories. In general, eating away from home also increases calorie intake.

Inactivity.
Sedentary people are more likely to gain weight because they don't burn calories through physical activities.

Quitting smoking.
Smokers tend to gain weight after quitting. This weight gain may be partially due to nicotine's ability to raise the rate at which your body burns calories (metabolic rate). When smokers stop, they burn fewer calories. Smoking also affects taste; quitting smoking makes food taste and smell better. Former smokers often gain weight because they eat more after they quit. However, cigarette smoking is still considered a greater threat to your health than is extra weight.

Pregnancy.
During pregnancy a woman's weight necessarily increases. Some women find this weight difficult to lose after the baby is born. This weight gain may contribute to the development of obesity in women.

Certain medications.
Corticosteroids and tricyclic antidepressants, in particular, can lead to weight gain. So can some high blood pressure and antipsychotic medications.

Medical problems.
Uncommonly, obesity can be traced to a medical cause, such as low thyroid function or excess production of hormones by the adrenal glands. As long as your thyroid releases the proper amounts of these hormones, your system functions normally. But sometimes your thyroid doesn't produce enough hormones, upsetting the balance of chemical reactions in your body. This condition is known as hypothyroidism, or underactive thyroid disease.

Women, especially those older than 50, are more likely to have hypothyroidism than men are. Hypothyroidism seldom causes symptoms in the early stages, but over time, untreated hypothyroidism can cause a number of health problems, such as obesity, joint pain, infertility and heart disease. Cushing's syndrome is a condition that occurs when your body is exposed to high levels of the hormone cortisol for a prolonged period of time. Sometimes called hypercortisolism, Cushing's syndrome can occur when your adrenal glands, located above your kidneys, make too much cortisol. It may also develop if you're taking high doses of cortisol-like medications (corticosteroids) for a prolonged period.

Too much cortisol can produce some of the hallmark signs of Cushing's syndrome — a fatty hump between your shoulders, a rounded face, and pink or purple stretch marks on your skin. It can also result in high blood pressure, bone loss and, on occasion, diabetes

A low metabolic rate is unlikely to cause obesity.
In addition, it's unclear whether polycystic ovarian syndrome contributes to obesity. Some medical problems, such as arthritis, can lead to decreased activity, which may result in weight gain.

Factors that increase your risk of obesity include:

Genetics.
Your genes may affect the amount of body fat you store and where that fat is distributed. Genetics may also play a role in how efficiently your body converts food into energy and how your body burns calories during exercise. Your genetic makeup doesn't guarantee that you'll be obese, however.

Family history.
If one or both of your parents are obese, your chances of being obese are greater. This may be due to shared genes or to a shared environment, which may include high-calorie foods and inactivity.

Age.
As you get older, you tend to be less active. In addition, the amount of muscle in your body tends to decrease with age. This lower muscle mass leads to a decrease in metabolism. These changes also reduce calorie needs. If you don't decrease your caloric intake as you age, you'll likely gain weight.

Sex.
Women are more likely to be obese than are men. Women have less muscle mass and tend to burn fewer calories at rest than men do.

The most important part of being a normal weight isn't looking a certain way - it's feeling good and staying healthy. Having too much body fat can be harmful to the body in many ways.

Obesity can run in families, but just how much is due to genes is hard to determine. Many families eat the same foods, have the same habits (like snacking in front of the TV), and tend to think alike when it comes to weight issues (like urging children to eat a lot at dinner so they can grow "big and strong"). All of these situations can contribute to weight gain, so it can be difficult to figure out if a person is born with a tendency to be obese or overweight or learns eating and exercise habits that lead to weight gain. In most cases, weight problems arise from a combination of habits and genetic factors.