(MayoClinic.com) It's best to lose weight with a healthy diet and regular physical activity. However, if you've tried to lose weight that way but haven't been able to — and you have health problems because of your weight — gastric bypass surgery may be an option.

Gastric bypass surgery (Roux-en-Y gastric bypass) is the most common type of weight-loss surgery, also called bariatric surgery. In gastric bypass surgery, the stomach is divided into two parts. Food travels from the smaller upper part of the stomach, called the "pouch," to the small intestine. Food no longer travels through the remaining larger part of the stomach. This change in the anatomy of your digestive system limits the amount of food that you can eat and that your body can digest, which helps with weight loss.

Gastric bypass surgery isn't for everyone, however. Like any major procedure, it has significant health risks and side effects. In addition, long-term success ultimately depends on your ability to make permanent changes in your lifestyle. For all these reasons, candidates for gastric bypass surgery are carefully screened to determine who is likely to benefit from gastric bypass surgery despite the risks.

You must meet certain medical guidelines to qualify for gastric bypass surgery. In general, you must:

• Be unable to achieve or maintain a healthy weight through diet and exercise
• Have a body mass index (BMI) of 40 or higher (extreme obesity)
• Have a BMI of 35 to 39.9 and also have a serious weight-related health problem, such as diabetes or high blood pressure

The criteria aren't without controversy, though. Some advocates of gastric bypass surgery believe that the criteria should be relaxed to make it an option for people with a BMI lower than 35.

A team of health professionals — usually including a doctor, dietitian, psychologist and surgeon — will evaluate whether gastric bypass surgery is appropriate for you. The evaluation essentially determines if the health benefits outweigh the potentially serious risks of this major procedure. Even if you meet the criteria for gastric bypass surgery, you will still need to be evaluated to see if you're psychologically and medically ready to undergo the procedure.

When conducting an evaluation, the team will consider:

• Your nutrition and weight history. The team reviews your weight trends, diet attempts, eating habits, exercise regimen, stress level, time constraints, motivation and other factors.
• Your medical condition. Some health problems increase the risks associated with having surgery or may be worsened by surgery, such as blood clots, liver disease, heart problems, kidney stones and nutritional deficiencies. The team will evaluate what medications you take, how much alcohol you drink and whether you smoke. You also will have a thorough physical exam and laboratory testing.
• Your psychological status. Certain mental health conditions may contribute to obesity or make it more difficult for you to maintain the health benefits of gastric bypass surgery. These may include binge-eating disorder, substance abuse, depression, anxiety disorders and issues related to childhood sexual abuse. While these may not prevent you from having gastric bypass surgery, your doctors may want to postpone surgery to ensure that any condition is appropriately treated and managed.
• Your motivation. The team will also assess your willingness and ability to follow through with recommendations made by your health care team and to carry out prescribed changes in your diet and exercise routine.
• Your age. Although there's no specific age limit for gastric bypass surgery, the risks increase if you're over age 65. The surgery remains controversial in people under age 18.

If you're approved for gastric bypass surgery, your health care team will give you instructions about how to prepare in the months or weeks before the surgery. These may include restrictions on eating and drinking, undergoing lifestyle counseling to help you cope with big changes in diet and exercise, quitting smoking, and starting a supervised physical activity program.

Even after gastric bypass surgery is scheduled, it can be delayed or canceled if your health care team determines that:

• You're not psychologically or medically ready for surgery
• You haven't made appropriate changes in your eating or exercise habits
• You've gained weight during the evaluation process, which makes surgery too risky

If it's determined that gastric bypass surgery is appropriate for you, you will still have financial hurdles to negotiate. If you plan to rely on health insurance coverage for your gastric bypass surgery, you likely will need to get preapproval from your health insurance company, Medicare or your state medical assistance program — whoever you have insurance through. The preapproval process typically requires documentation from your team of doctors that justifies your medical need for gastric bypass surgery.

Different health insurers have different requirements to prove your medical need for gastric bypass surgery. Your health insurer may not cover gastric bypass surgery at all or may cover only parts of the process. In some cases, you may have to meet requirements, such as losing a specific amount of weight, before your insurance will grant approval. To avoid unpleasant financial surprises, check to see what specific services are covered. You may have to pay for some portion of the costs yourself.

Gastric bypass surgery isn't a miracle procedure — and it isn't for everyone. Having gastric bypass surgery doesn't guarantee that you'll lose all your excess weight or that you'll keep it off over the long term. Nor is it a way to avoid making changes in your diet and exercise habits. In fact, you can regain the weight you lose with gastric bypass surgery if you don't stick with the lifestyle changes. Still, gastric bypass surgery has helped many people lose weight and improve their health. If you think gastric bypass surgery might be right for you, talk with your doctor.

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