Comparison of DS and RNY

doctor and patient
In this section a comparison of DS and RNY bariatric procedures will be made explaining the biological differences in anatomy, how the changes affect the body and the impact they could have on a patient’s lifestyle. Both Roux-en-Y Gastric Bypass (RNY) and Duodenal Switch (DS) contain restrictive and varying degree of malabsorption components, an examination of those differences will then be compared to excess weight loss long term and resolution of comorbidities in both procedures.


Restrictive Component


A pouch is created at the top part of the stomach to restrict the amount of food a patient can eat. The lower part of the stomach that is no longer used is called the bypassed stomach. Food passes through the anastomosis (connection-stoma) created between the pouch and the small intestine, which is deliberately made quite narrow to keep food in the pouch longer, thus making the patient feel fuller longer. The pylorus is at the bottom of the bypassed stomach and is no longer able to regulate the flow of food into the small intestine. This is the reason why some patients who consume food with high sugar or fat content develop dumping syndrome manifested by high hearth rate, palpitation, nausea, vomiting, and/or explosive diarrhea.

The stomach “pouch” is reduced to10 – 30 mL in volume following surgery [51] but will stretch over time.

Weight maintenance is achieved through caloric restriction.



Dumping is the unpleasant and uncomfortable experience that some gastric bypass patients experience. This is caused by unregulated and an uncontrolled flow of food in the small bowel. The symptoms can be divided in to Early and Late Dumping.

“Early” dumping begins during or right after a meal; symptoms include nausea, vomiting, bloating, cramping, diarrhea, dizziness and fatigue.

“Late” dumping happens 1 to 3 hours after eating; symptoms include weakness, sweating, and dizziness. Some patients choose RNY surgery because they prefer the possibility of “dumping” to help them control eating junk food containing sugar or fat. Approximately 70%-76% of patients dump. [60-64] Patients dump with different foods, some never dump, some only on certain quantities, and some “outgrow” it. Also note, that there is no scientific evidence that shows any benefit to dumping in gastric bypass patients will help them maintain their weight loss. [71]



Standard diagnostic techniques can be used on the “pouch” stomach. The “blind” stomach is inaccessible to standard non-evasive diagnostic tools like x-ray and endoscope. It makes it extremely difficult to identify ulcers or masses in the “bypassed” stomach.

“Normally if a patient develops ulcer symptoms, a gastroenterologist can look into the stomach with an endoscope and make the diagnosis of an ulcer. If that ulcer is bleeding, the gastroenterologist can also treat the ulcer to stop it from bleeding by injecting a drug into it or putting some electric current on the ulcer to coagulate it. These options are taken away once you have a RNY bypass”. [59] The blind stomach can only be scoped, under general anesthesia, through a small incision on the abdomen wall, and advancing the scope through the incision into the blind stomach.

The tissue at the anastomosis, between the stomach and small intestine, has lost some of its blood supply making it more fragile, and increases the risk of ulceration. Smoking will increase the risk of ulceration in the anastomosis area as well.



Taking Aspirin or non-steroidal anti-inflammatory drugs (NSAIDs) causes increased risk for ulcers. Since diagnosing and treating ulcers is so difficult in RNY patients due to the fragile state of the anastomosis, many surgeons do not recommend RNY patients take NSAIDs following surgery. NSAIDs include Ibuprofen (Advil, Motrin), Naproxen (Naprosyn, Aleve) etc.



About 70% of the outer curvature of the stomach is removed, which reduces the amount of food a patient can eat. The stomach retains normal function, the pylorus continues to control food moving from the stomach into the intestine, and as a result DS patients do not experience “dumping”.

A benefit of removing a portion of the stomach is that it also greatly reduces the amount of ghrelin producing tissue and the amount of acid. Ghrelin is the “hunger hormone” and reducing the amount produced suppresses the appetite.

The remaining stomach is about 3-5 ounces and holds approximately 90 to 150mL in volume. After DS, patients can consume a wide variety of foods and after about a year they can consume approximately half of their preoperative volume. [2]

A DS patient’s stomach is probably the largest out of all other weight loss surgical procedures. The reason is DS weight loss is maintained through malabsorption rather than caloric restriction and the increased protein requirement means more room is needed to consume 100 grams of protein a day. DS patients don’t dump because their pylorus remains in use, so there are no food’s they “can’t” eat. With this freedom comes responsibility, patients need to eat protein based meals following the surgery to stay healthy.

Some patients choose DS surgery because they prefer unrestricted food options or they need to continue taking NSAIDs.


Malabsorption Component

The small intestine consists of 3 sections; duodenum, jejunum and ileum. Vitamins and minerals are absorbed in different sections of the small intestine; bypassing different sections will result in different supplement needs.



The small bowel is divided about 45 cm below the lower stomach. The entire duodenum and a little bit of the jejunum are bypassed.

  • Vitamin and mineral supplementation is vital, which require maintaining good health.
  • Routine blood work is mandatory. Adjust supplements as necessary.
  • Basic vitamin requirements are multivitamins, calcium citrate, B12, B1, and iron.



The small bowel is divided approximately 2 inches into the duodenum. The common channel, where food and bile mix and nutrients are absorbed, is usually 75 – 100 cm.

  • This allows a patient to only absorb 20% of the fat they consume. Eating too much fat can cause loose stools. The inability to absorb fats also interferes with absorption of the fat-soluble vitamins A, D, E & K.
  • This allows a patient to only absorb approximately 60% of the protein they consume. Patients must intake between 80-120g of protein a day.
  • This allows a patient to only absorb 60% of complex carbohydrates and 100% of simple carbohydrates.
  • Gas and stool tend to be stronger smelling due to the intestine re-routing and can be enhanced if a patient eats too many simple carbs.


It is important to bear in mind car service to lax airport during covid-19 and that the percentages given above are at best an estimation of extrapolated information of the relative length of the common channel, and alimentary length as a percentage of the total length.

Vitamin and mineral supplementation is vital and a requirement to maintaining good health.

Routine blood work is mandatory and adjustment of supplements as necessary. Unfortunately, patients get a false sense of security with the resolution of the comorbidities after weight loss surgery, and fail to follow up with their bariatric surgeon or a primary care physician who has an in-depth understanding of, not only the particular surgery, but also the details of the laboratory studies needed. A common example is when patients return to a surgeon’s office with a very low Vitamin D level, and having only had Calcium levels checked by their primary care for years. Note that Calcium levels will remain normal for some time even with low Vitamin D levels.

Weight maintenance is achieved through malabsorption. The malabsorption component is attributed to the higher percentage excess weight loss (EWL) long term when compared to other bariatric procedures.

Basic vitamin requirements are multivitamins, calcium citrate, vitamin A, vitamin D, and zinc.


Excess Weight Loss (EWL)

Excess weight loss percentages can be calculated by determining pounds lost divided by total excess pounds. The RNY and DS statistics for excess weight loss percentages can be found in the AACE/TOS/ASMBS Guidelines. [51]



EWL% at 1-2 years 48%-85%

EWL% at 3-6 years 53%-77%

EWL% at 7-10 years 25%-68%



EWL% at 1-2 years 65%-83%

EWL% at 3-6 years 62%-81%

EWL% at 7-10 years 60%-80%


Resolution of Comorbidities

Following bariatric surgery, many obesity related comorbidities can be improved or cured. The RNY and DS statistics for the resolution of comorbidities can be found in Buchwald et al. Bariatric Surgery: A Systematic Review and Meta-Analysis. [58]



Type 2 Diabetes 84%

Hyperlipidemia 97%

Hypertension 68%

Sleep Apnea 80%



Type 2 Diabetes 99%

Hyperlipidemia 99%

Hypertension 83%

Sleep Apnea 92%


The Duodenal Switch weight loss surgery procedure has seen the highest rate of type 2 diabetes cure (remission), often before leaving the hospital following surgery! For more information on how DS surgery can have such a quick result, see the metabolic effect in our section on the Duodenal Switch Procedure.


Additional Comparisons

Central Valley Bariatrics

Weight Loss Surgery Procedures and Outcome