Your weight essentially relies on your net calories. However, many other factors influence this formula, whether directly or indirectly, including the process of aging.

The key to gaining weight is consistently eating more calories than your body uses. While raw eggs provide some calories, lots of other healthy foods contain more calories per serving, so simply drinking raw eggs may not be the best way to gain weight.

If you experience a rapid change in weight or appetite or suffer from bloating, you should consult with your doctor to test for serious health problems. Keep track of any other symptoms you experience, any changes in your diet and any medications you take to help rule out or confirm potential causes.

If you have a high metabolism, you have to eat more calories than most people just to maintain your weight. If you are active on your active job or practice sports frequently, putting on pounds can become a great challenge.

Infrequent bowel movements and excess body fat often go hand in hand, so it may seem logical to assume that they are related. But while there is often a correlation, neither condition causes the other.

Approximately 2 percent of people in the United States are underweight, and some of these people have trouble gaining weight no matter what they try. You could be one of these people, or you could be underestimating how many calories you're burning during the day or overestimating how much you're really eating.

The media may glorify rail-thin actresses and size 0 models, but being underweight, which means a body mass index below 18.5, is a serious matter with distinct health consequences.

Your lifestyle, certain medications and illness can squash your appetite, leading to possible unintentional weight loss that endangers your health. If you are too thin and have a body mass index of less than 18.5, this can compromise your immunity, energy, hormonal function and bone health.

Gaining weight can take as much effort as losing it. A caloric surplus, which involves consuming a greater number of calories than you burn, helps you put on pounds. No specific vitamin, regardless of its claims, will make you gain weight -- vitamins don't contain calories.

You can use many different training methods to build muscle. Pyramid sets, drop sets, straight sets, and wave loading are all very popular and can enable you to put on muscle.

Working with genetic and environmental influences on the body's internal clock, the hormone melatonin regulates daily biological functions of sleep, immune function and metabolism.

Some bodybuilders achieve muscle growth by bulking -- increasing weight and presumably -- muscle by overeating. They then "cut" when going into the competition season by prioritizing fat loss and maintaining any muscle the bulking helped them build.