Losing weight despite a big appetite can be cause for concern, especially if it happens within a short period of time. Endocrine disorders, such as diabetes or hyperthyroidism, have weight loss and increased appetite as their major symptoms. Weight loss and a healthy appetite could just be part of a natural process if you are just starting an exercise program. If you experience sudden weight loss and and have an increased appetite, it's best to contact your doctor immediately.
One of the most common explanations for weight loss despite a healthy appetite, hyperthyroidism is an endocrine disorder caused by the thyroid gland producing too much of the hormone thyroxine. Hyperthyroidism will usually have other symptoms along with it; nervousness, irritability, sweating and a rapid or irregular heartbeat are common. You may also feel very fatigued, have trouble sleeping, or a swollen neck. Consult a doctor right away if these symptoms are present.
Problems with the gastrointestinal tract, where food absorption takes place, can also be responsible for weight loss despite a healthy appetite. These disorders -- referred to as "malabsorption syndromes" -- will have other symptoms along with the weight loss and appetite, including fat in the stool, diarrhea, flatulence, cramps and bloating. Crohn's disease, celiac disease and even parasitic infections all affect the gastrointestinal system and block nutrients from being absorbed into the body. All of them are serious and should be treated as soon as possible, so consult a doctor if any of these symptoms appear.
There are two types of diabetes, aptly named type 1 and type 2. Type 1 diabetes is usually diagnosed in childhood but can occur later in life. It is caused by lack of insulin, which is the hormone that regulates the amount of sugar in the blood. Symptoms of type 1 diabetes include weight loss and increased appetite, fatigue, increased thirst and urination, and nausea and vomiting. Type 2 diabetes is caused by resistance to insulin. It has similar symptoms as type 1 but does not usually have weight loss as one of them. If you experience these symptoms, contact your doctor as soon as possible. Left untreated they can both lead to serious health issues.
Not all problems associated with weight loss and a hearty appetite are the result of an underlying disorder. For example, if you are starting a workout regimen your appetite will often increase. If you don't compensate by eating more, you will often experience weight loss. Eating less fat, skipping meals, or having a very busy schedule that distracts you can also contribute. Consider if one of these factors is causing your weight loss.
Unexplained weight loss can be a serious issue, especially if it happens quickly. Consulting your doctor is the safest thing to do in these cases. A doctor can test to see what issues, some of them serious, could be causing the problem. Cancer, drug use, depression and eating disorders, such as bulimia, can all cause rapid weight loss, even if your appetite is increased.