Gastric Bypass surgery is a weight loss procedure used recombination with a healthy, balanced diet and exercise. A gastric bypass helps in 4 main ways:

1. Stomach size is reduced: to a small pouch around 25ml in size. This reduces the amount of food that can be eaten at mealtimes before feeling satisfied – none of the stomach is removed in a gastric bypass procedure.

2. Narrow opening into small intestine: Food leaves the new ‘stomach pouch’ via a narrow opening, therefore passes slowly into the small intestine. This causes you to feel satisfied for a longer period on the same amount of food.

3. Not all calories absorbed: This is due to food not passing through the main part of the stomach and the first part of the small intestine.

4. Changes in gut hormones: the structural changes of the digestive system are associated with hormonal changes in the stomach and intestines. These hormones contribute towards reduced hunger and increased satisfaction.

Digestive alterations:

The digestive alterations of gastric bypass surgery result in less vitamins and minerals being absorbed from food, therefore supplements are mandatory to ensure long-term success. It is essential that you take the recommended supplements as you will be consuming a reduced volume of food. Taking complete multivitamin and mineral supplements twice daily is recommended along with vitamin D and calcium (to protect your bones), and iron (to help maintain energy levels).

Most of the weight lost following a Gastric Bypass occurs in the first 12-18 months, with the average weight loss being 55-70% of your excess weight after 3 years. The dietitian will discuss your excess weight loss at each postoperative appointment. The rate and total amount of weight loss depends on several factors:

1. Initial weight/BMI – People with a higher starting BMI tend to see greater week-by-week loss.

2. Gender – Men tend to lose weight faster than women, due to men having a higher muscle mass than women. The more muscle you have, the more calories you burn, even at rest.

3. Diet – Eating healthily and limiting high calorie foods and alcohol helps give the best results from surgery.

4. Exercise – Patients who increase their physical activity level lose more weight than those who do not. There are many other benefits of being more physically active following surgery aside from optimising weight loss and increasing metabolic rate. These include muscle toning, improving posture as well as helping to boost self-esteem, mood and sleep quality.

Achieving the best results

Judge your progress by how your clothes fit as well as by actual weight loss. Sometimes your weight loss may be slow but you could be losing inches, especially if exercising. To achieve the best results, you must stick to the eating regime and follow dietitian’s advice.

Gastric Bypass Surgery is often preferred by surgeons as it is considered the “gold standard” of weight loss surgery, having been around the longest (over 40 years) and with the highest weight loss. However, all major weight loss surgeries including gastric bypass need to be considered very carefully. One restriction of gastric bypass surgery is your body mass index (BMI). Having a BMI of 40 or higher is a requirement for the surgery to be performed in most cases, although if you have health conditions related to being obese (especially Type 2 Diabetes), you may be considered with a BMI of 35 or higher (lower if you are from an Asian background).

Gastric Bypass surgery is one of the most successful bariatric surgery procedures; here’s why:

Weight loss. The Journal of Obesity, 2013, found an average of 77.5% excess weight loss after 18 months.

Can’t eat large meals. Due to restricted stomach size you physically can’t eat large meals.

Dumping syndrome. Up to 70% of patients feel unwell from eating excessive amount of carbohydrates and/or sugars.

Less calories absorbed. Due to the bypass of the intestines.

Diabetes help. Improved type 2 diabetes due to small intestine spontaneously producing a hormone that helps the body use glucose.

Hormonal changes. Changes in gut hormones help you to feel less hungry and satisfied on smaller portions.

Long term success. The large majority of patients maintain more than 50% of excess weight loss following surgery.


A Gastric Bypass is an effective form of weight loss surgery that is well studied. With this procedure, long term excellent results have consistently demonstrated themselves.

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