Weight loss and weight gain rely on the balance of calories in, which are obtained through your diet, and calories out, which is the energy you burn throughout the day.

Approximately 40 percent of Americans are overweight. Usually people gain weight at a slow, almost unnoticeable rate over months or years. However, some conditions can cause sudden weight gain in a week or so.

Physicians prescribe prednisone, a corticosteroid medication, when your body is not making enough corticosteroids due to illness and inflammation. These conditions include arthritis, multiple sclerosis, Crohn’s disease, lupus and certain cancer types.

If you find yourself gaining weight or struggling to drop pounds, you may need to consider your digestive system. Over 60 million Americans experience digestive disorders including bloating, heartburn, constipation, diarrhea and gas, according to the NJ Nutritionist website.

When you gain weight, it usually creeps on slowly over several weeks or months -- not all at once in one day. Weight gain occurs when you consume more calories than you burn. A 3,500-calorie surplus -- 3,500 calories in addition to those you use every day -- will make you gain about 1 pound.

Both male and female bodies produce natural testosterone, although women produce only small amounts of this hormone. Methyltestosterone is a synthetic form of testosterone. Even though testosterone replacement therapy is more common for men, women may also benefit from this drug.

Excess weight in your stomach is not just a cosmetic issue, it can have severe implications for your health. Those who carry extra abdominal -- or visceral -- fat have an increased risk of experiencing metabolic disturbances and developing cardiovascular disease and Type 2 diabetes (references 4).

No matter how committed you are to your weight loss plan, sometimes life just gets in the way and you are forced to skip a workout. It's easy to picture all of your hard work going down the drain while you're sick in bed or working late.

If you notice your weight has gone up right after you've had a glass of water or a fiber-rich snack, don't worry. Water and fiber don't cause permanent weight gain; in fact, they're often linked to weight loss.

Ativan, the brand name for the generic medication lorazepam, has long been used as an anti-anxiety drug. Ativan belongs to a class of drugs called benzodiazepines, which act as central nervous system depressants. Weight gain isn't a common side of a Ativan, but could occur in some individuals.

Glutamine is an amino acid essential for muscle strength. It serves as a building block to protein, helping to synthesize this nutrient in the body. Due to its necessity in the maintenance of muscles, questions still remain about this amino acid's effect on weight.

Caffeine is in a number of foods, including tea, coffee, chocolate, energy drinks and some types of soft drinks. It's even an ingredient in certain medications.