Almost 3 out of every 10 adults in the United States are obese. Body Mass Index (BMI) is a popular method of defining a healthy weight vs. being underweight, overweight or obese. It should be used as a guide, along with waist size, to help estimate the amount of body fat. A BMI of 25 to 29.9 is considered overweight and one 30 or above is considered obese.

Researchers are actively studying the complex mechanisms for obesity. It's clear that many factors contribute: Our high-calorie diet gets much of the blame, and it's true that some of our favorite foods — hamburgers and hot dogs, ice cream, cake, candy, chips and other snack foods — are loaded with calories. Genes determine your body type and, to a certain degree, how much you weigh. If you're female and your mother carried fat on her hips and thighs, you probably will too.

While body shape is largely determined by genetics, lifestyle choices can have an enormous influence on body weight. Eating on the run and lack of exercise contribute to obesity. It should be remembered that despite problems of weight management, most of us have a finely tune mechanism geared toward keeping weight stable. For example, a typical American gains approximately 20 pounds between 25 and 55 years of age. It is estimated that an adult consumes 900,000 to 1 million calories per year and the additional 20 pounds accounts for only a few tenths of one percent of ingested calories.

Some people are clearly more vulnerable to obesity than others. Factors such as the number of fat cells you have, what your weight set point is, and how much you fidget are genetically determined. This does not mean that maintaining a healthy weight is out of your control. It does mean that you may have a harder time losing weight and keeping it off — even if you practice a healthier lifestyle and monitor your diet.

People who are constantly moving and fidgeting tend to be thinner. Like many of other behaviors, the "fidget factor" is almost surely genetic. However, even if you were not born with the "fidget gene," you can burn those extra calories with a conscious effort. For instance, keep moving your legs while sitting at work or at home, get up and move around often, and take short walks around the office and home at every opportunity.

If your family history tells you that you are prone to obesity, limiting calories and exercising regularly starting at a young age must be priorities in your life.

To lose weight, you must take in fewer calories than you use. Some people will never reach an ideal or desirable weight, but everyone who is overweight can certainly lose some of those extra pounds and maintain a healthier weight. Be realistic and maintain a positive attitude. Accept the fact that permanent weight loss is a slow process. The following guidelines may help:

• Set short-term, achievable goals. If you need to lose 70 pounds, first set your goal at losing 5 or 10. Reaching a short-term goal may give you the motivation to keep going toward the larger, more distant goal.
• Don't go on a crash diet. Instead, think long-term. Change your eating habits so that your meals and snacks are balanced with a variety of healthy foods. Eat the foods you like to eat, but master portion control.
• Increase your activity. Pick an exercise routine that suits your lifestyle so you'll stick with it. Take lessons to learn a new sport such as tennis, racquetball or golf. If you can't join a gym or you're not interested in sports, find everyday ways to exercise. Walk to and from work every day, or take a brisk walk during your lunch hour. Skip the elevator and walk up and down the stairs. Leave your car some distance from where you're headed so you have to walk part way.
• Don't give up. After losing the first few pounds, you may reach a plateau where your weight will stay steady for weeks even though you're watching your calories and exercising regularly. Stick with your program. It is likely that your body will adjust to the new fat and calorie levels you've introduced and you'll continue to lose weight. Don't immediately cut back further on calories. If you stop losing weight or begin to regain a couple of pounds, try increasing your amount of daily activity first. Then cut calories by about 5 percent if you are not making progress.
• Give yourself a break. Don't get obsessive about weight loss. If you blow it one night and overeat, just get back on the plan the following day. One binge won't destroy all your good work.
• Work with your doctor. If you are not gradually losing weight as expected or your weight is dropping dramatically, contact your doctor.