Numerous conditions can cause sudden, unintentional weight gain. According to the MedlinePlus website, unintentional weight gain is an increase in your body weight that occurs when you consume more calories than your body uses.

Low body weight, also known as failure to thrive in children age 2 or under, can lead to serious repercussions for your toddler.

Irregular periods are not uncommon, and weight gain is linked with irregular menstruation in at least two ways. Weight gain and obesity might be considered a cause of an irregular period, or weight gain and an irregular period might be symptoms of a larger health issue.

Insects have a way of flying into places they don't belong, including the human eye. Visor helmets and glasses may protect your eyes when you're riding a motorcycle or bicycle, but bugs can land in your eyes when you're just walking along the street.

When men approach middle age, they tend to gain weight, especially around the midsection. While this is avoidable, several factors fall into place during this time of life, leading to an increase of fat storage and loss of muscle tone.

Weight gainers are nutritional supplements that can help you gain weight and add muscle. Weight gainers usually come in the form of powdered protein that can be mixed with water, milk or juice. If you are attempting to gain muscle, you must increase your overall caloric intake and consume adequate amounts of protein.

While many individuals struggle with excess amounts of body fat, some people have a hard time gaining weight. Depo-Provera, often called Depo, is a prescription contraceptive drug that contains progestin. Your doctor must prescribe and administer this injectible contraceptive once every three months.

When you need to fill out to look and feel healthier, add quality calories to your meals to encourage weight gain. To gain weight, your caloric intake must exceed what you burn in a day through basic body functions like pumping blood, plus other activities such as doing chores and exercising.

A long endurance session or tough weight-training workout requires post-workout fueling to help replenish your energy stores and repair your muscles. That snack or meal won't cause you to gain weight, unless it pushes you above the number of calories you need to maintain your weight.

Many women would like to lose a few pounds, but if you'd like to put on pounds instead, you may find it to be a challenge. To gain weight, you'll need to increase your calories, and if you have a small appetite, you may want to try some other ways to boost your intake, in addition to your regular meals and snacks.

As you reach age 50, your body naturally loses muscle mass and starts to pack on extra pounds in your midsection. This increased belly fat is a health concern that raises your risk of chronic disease.

While everyone is born with a genetically determined body type -- for example, a pear, apple or banana shape -- lifestyle modifications like diet and exercise can slightly change the shape of your physique.