gastric bypass

Gastric Bypass-How It Works, Pros & Cons and Vitamins

December 31, 2015

According to the Center for Disease Control and Prevention, approximately 78.6 million adult Americans are affected by obesity. A person with a BMI of 30 kg/m² or greater is considered obese. Obesity increases one’s risk of developing type 2 diabetes, heart disease, stroke and certain types of cancer (1).  Weight loss surgery is a treatment that can be considered by persons that are morbidly obese.

How the Roux-en-Y Gastric Bypass (RNY) Works


Treatment options are available to those who suffer from severe obesity (BMI of 40 kg/m² or greater) and one of those treatment options is Bariatric (weight loss) surgery (2). The most commonly performed bariatric procedure is the Roux-en-Y Gastric Bypass (RNY), often referred to as Gastric Bypass. According to the American Society for Metabolic and Bariatric Surgery (ASMBS), the RNY is considered the "gold standard’ of weight loss surgery."  The RNY has two components - restriction and malabsorption, that work together to produce weight loss.

This procedure is considered restrictive because a portion of the upper stomach is made into a “pouch”. Think of this as a “new stomach” meaning that food will be entering the “pouch” and no longer into the remaining portion of the stomach. This “pouch” significantly reduces consumption because it can hold no more than 1 cup, or less, of food at a time.

The RNY pouch helps to reduce portions, which reduces the amount of calories consumed. If calories consumed exceed calories burned, this could lead to weight gain thus consuming less calories aids with weight loss. The malabsorptive portion of the procedure is dividing the small intestine, and connecting the bottom portion of the small intestine to the “pouch”. The remaining part of the small intestine (top portion) is then connected to a lower portion of the small intestine. This creates a “bypass” in the digestive process, meaning that part of the small intestine is bypassed, therefore, calorie and nutrient absorption is decreased (3).

Advantages and Disadvantages to the RNY

The RNY has advantages to aid weight loss and few disadvantages. Advantages include favorable hormonal changes such as Grehlin. The gastric bypass reduces appetite and improves satiety, which are hormonal changes that ultimately lead to significant long-term weight loss.

A disadvantage of the procedure is potential nutrient malabsorption deficiencies due to less consumption and decreased absorption of nutrients in food (3). Nutritional deficiencies mean that there is an inadequate supply of essential vitamins and minerals that are necessary to keep us healthy. Fortunately, this disadvantage can be avoided with appropriate diet, and life-long vitamin and mineral supplementation. On-going follow up after surgery is necessary to continue to avoid, treat and monitor existing nutritional deficiencies.

Vitamin Supplementation is Important

Following surgery, it is important to incorporate meals that focus on protein followed up by a healthy diet of fruits and vegetables. Fruits and vegetables are rich in vitamins and minerals, which can also help vitamin levels in addition to supplements.

Since adequate nutrition is crucial following weight loss surgery, the ASMBS has established recommendations for patients following RNY surgery. Their recommendations include these supplements following surgery: multivitamin with iron, vitamin D, calcium and vitamin B12. Although these specific supplements are recommended by the ASMBS, individual vitamin supplementation is determined by the surgeon and/or dietitian.

A multivitamin daily that contains 18-27 mg/dL iron and 200% of daily value for at least 2/3 of the nutrients listed on the Supplement Facts label is recommended. This is defined as a high potency vitamin. Vitamin D and calcium aid with bone health. An insufficient amount of vitamin D and calcium could lead to thin and brittle bones. Therefore, the ASMBS recommends 2,000 IU of vitamin D and 1,500-2,000mg calcium citrate daily.

It is advised to separate calcium supplements in 500mg-600mg doses throughout the day and to not take a multivitamin with iron at the same time as calcium, preferably separated by at least two hours. This will help enhance absorption of iron from the multivitamin.  A vitamin B12 supplement, 350-500µg per day is recommended in a crystalline form to enhance absorption of vitamin B12 (4). Vitamin B12 is needed for proper red blood cell formation and neurological function (5).

Check with a surgeon or dietitian for specific vitamin and mineral supplement recommendations, as vitamin or mineral supplements may be determined on an individual basis depending on medical history, existing current medical conditions and laboratory blood results. Follow up care is a key component to not only weight loss and maintenance, but to prevent and treat nutritional deficiencies. If left untreated, nutritional deficiencies could lead to serious medical conditions.


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Photo credit for RNY image:  ASMBS

Tess Lockhart


Tess Lockhart R.D., L.D. is a registered and licensed dietitian who received her degree from the University of Akron in Science and Dietetics. She also completed her internship at the University of Akron through the Coordinated Program in Dietetics. Tess is an outpatient Bariatric nutritional counselor at Summa Health Center. She completes nutrition evaluations to assess dietary habits of pre-operative patients to prepare for healthy lifestyle changes following surgery. She also focuses on providing weight management nutrition counseling to post-operative patients to assist with goal setting, achieving optimum nutrition status and appropriate vitamin supplementation.