Look around. As a nation, we have become increasingly overweight. A few pounds here. A few pounds there. Next thing you know, you're tipping the scales with numbers you never dreamed you'd see.

Today, a whopping two-thirds of Americans are overweight, and one-third of the nation is obese. Perhaps most troubling of all, the numbers of overweight and obese children are also on the rise, a phenomenon that promises to push epidemic rates of diabetes, heart disease, and certain cancers well into the next generation.

Obesity is technically defined as having a BMI of 30 or more. (See Chapter 15 for more on BMI.) Being obese is not just about being overweight. People who are obese have extra amounts of fat on their bodies.

It would be easy if everyone could blame their thyroid or their genes for their excess weight. But the truth is obesity is most often a problem of inactivity and eating too much. Too much time spent in front of the television and computer, overlarge portions, and lack of time to prepare healthy meals and exercise are also contributors. Over time, these habits can result in steady increases in body weight, which can eventually lead to obesity.

The Thyroid Link

In people who have hypothyroidism, metabolism slows down. When that happens, you're more likely to gain weight (though often not enough to constitute obesity). Other problems that add to the weight gain include bloating, constipation, and fatigue, which can make it hard for you to pursue physical activities.

Research suggests that thyroid hormones may also be involved in the body's secretion of and ability to use leptin, a hormone involved in fat storage. In healthy people, leptin sends a signal to the brain to stop eating and that there is now enough fat stored. In people who are obese or overweight, the blood levels of leptin are actually higher than normal, but the brain can't receive the signals sent by leptin. Exactly how leptin is associated with thyroid disease, however, is unclear and a subject for research.

Why It's Bad

Obesity is harmful in many ways. For starters, it can take a serious toll on your quality of life. The most menial tasks can be physically exhausting. You may feel depressed, angry, and frustrated. Outings with friends may be fraught with embarrassment and shame. On the job, you may face discrimination, ostracism, and rejection by colleagues.

Obesity also raises your risk for serious health problems, including high blood pressure, high cholesterol, type 2 diabetes, and heart disease. It can lead to stroke and certain kinds of cancer. In people who have arthritis, obesity taxes the joints. It can also cause sleep apnea, which will perpetuate your fatigue. In addition, obesity can cause death. Experts estimate that obesity kills 300,000 people each year.

So, what can you do about it? The best defense against obesity is prevention. By adopting a healthy lifestyle that includes regular physical activity and good nutrition, most adults can stave off obesity and prevent the health problems associated with it. In terms of thyroid health, it means getting proper treatment and control of your thyroid disorder.