What is the most common complications of gastric bypass surgery?

A complication is an unexpected medical or psychological event occurring after surgery. Every effort is taken to prevent complications, but because of the magnitude of gastric bypass surgery and the many medical problems of many of the patients, complications do occur.

What is the most common complications of gastric bypass surgery?

Gastric Bypass Mortality

The death rate (mortality) from gastric bypass is about 1 out of 350 people (1/350). The mortality rate for gastric bypass is similar to the mortality rate for other major general surgical procedures done on a group of patients who are obese and have multiple health problems. Risk of dying from any procedure depends on the general health, age, and weight of the individual. Clearly people who are older, have more severe comorbid problems, and are heavier are much higher risk than younger, healthier, less obese counterparts. The most common causes of death after gastric bypass include infection secondary to staple line or suture line leaks, pulmonary embolism, and respiratory problems.

Early complications of gastric bypass surgery

(within the first 2 months after surgery)

5% of patients have some sort of significant complication. About 10% have some sort of minor problem that requires attention.

  • Anastamotic (staple line) leak <2%
  • Anesthetic problem Severe, rare
  • Arrythmia (cardiac irregularity) <1%
  • Blood clots to lungs (pulmonary embolism) <1%
  • Gastrostomy problems 2%
  • Heart attack (myocardial infarction) rare
  • Incision infection, major 2%
  • Incision infection, minor 3%
  • Incision opening (fascial dehiscence) rare
  • Kidney failure rare
  • Pneumonia 1%
  • Potassium deficiency rare
  • Stroke rare
  • Thrombophlebitis <1%
  • Transfusion 2%

Late complications of gastric bypass surgery

(after first two months after surgery)

  • Anastamotic ulcer <1%
  • Anastamotic stricture (last 300 patients) 1%
  • Anemia, iron deficiency Rare if iron replaced, common if not
  • B12 deficiency Rare if B12 replaced, 30% if no B12 suppliment
  • Incision hernia 10%
  • Potassium deficiency rare
  • Psychological challenges (significant) 5-10%
  • Small bowel obstruction <1%

This list is indicated to illustrate the type and frequency of complications following gastric bypass in our practice. The figures are comparable to nationally published figures. Some are a little higher and some are a little lower. Since most of the events are very rare, it is very difficult to tell small differences between one surgeon’s series and another’s with any statistical certainty. This list does not include all possible complications of gastric bypass surgery.

Gastric Bypass Complications: Iron Deficiency

Iron deficiency can be a problem following Gastric Bypass because iron is partially absorbed in the duodenum. The duodenum is bypassed along with the stomach. Iron deficiency can be a particular problem for women who lose blood (and thus iron) with their menses.

We recommend that all gastric bypass patients eat foods that are high in iron, and that iron and hemoglobin levels be checked once or twice a year. For menstruating women we suggest a daily iron supplement such as ferrous sulfate or ferrous gluconate 300 to 350mg per day.

Iron absorption seems to be enhanced by adequate Vitamin C intake. We suggest that all patients take a full potency multivitamin daily. Most multivitamins contain about 60mg Vitamin C. This should be adequate under normal conditions. When one is iron deficient and trying to replace iron stores, increasing Vitamin C intake to 500mg per day may be helpful.

Iron containing foods:

  • Organ meats such as liver
  • Meat, fish, and poultry
  • Shellfish, especially oysters
  • Dried beans and peas
  • Whole-grain products such as breads and cereals
  • Dark-green leafy vegetables such as spinach and broccoli
  • Dried fruits such as figs, raisins, apricots, and dates

Gastric Bypass Complications: Lactose Intolerance

Lactose, the natural sugar found in milk products, is digested in the small bowel by means of the enzyme lactase. About 10% of adults in the United States are lactose intolerant. They do not have enough lactase to digest milk. When they eat milk or milk products, they develop crampy abdominal pain, bloating and diarrhea. Lactose intolerance can be acquired after gastric bypass or other gastric surgeries by as many as 10% of patients. When a person with a normal stomach drinks milk, it accumulates in the stomach and then is released slowly into the small intestine. There is enough lactase available to handle a small amount of milk at a time. After gastric bypass, milk passes directly through the gastric pouch into the small bowel at a much higher rate. The milk overwhelms the available enzyme and the lactose intolerance symptoms occur.

The strategies to deal with lactose intolerance that develops after surgery are to take milk products more slowly, eat thicker products such as yogurt or cheese rather than liquids milk, avoid milk products all together, or take an enzyme substitute Lactaid with meals.

The following information on the lactose-controlled diet and use of lactaid was provided by Marylyn Swift, RD from a hospital dietary manual. The use of lactaid is described in the text.

Lactose-Controlled Diet

Purpose The lactose-controlled diet is designed to prevent or reduce gastrointestinal symptoms of bloating, flatulence, cramping, nausea, and diarrhea associated with consumption of the disaccharide lactose.

Use The lactose-controlled diet is indicated for individuals with lactose intolerance or lactase deficiency (also called lactase nonpersistence). Individuals with primary lactase deficiency tolerate various levels of lactose while those having rare congenital lactase deficiency require strict avoidance of lactose-containing foods. Secondary lactose intolerance or lactase deficiency is usually transient and develops secondary to illness or disease and often requires limitation or avoidance of lactose.


The diet is a general one that restricts or eliminates lactose-containing foods. Lactose is primarily found in dairy products but may be present as an ingredient or component of various food products. (See Table 1 for lactose content of common foods and beverages.) Depending on individual tolerance, limiting products with lactose may help to alleviate symptoms.

Labels should be read carefully to identify sources of lactose. Dairy products that include milk, milk solids, whey, lactose, curds, skim milk powder, skim milk solids, sweet or sour cream, buttermilk, or malted milk are sources of lactose. Other possible sources of lactose are breads, candy, cookies, cold cuts, hot dogs, bologna, commercial sauces and gravies, dessert mixes, cream soups, some ready-to-eat cereals, frostings, chocolate drink mixes, salad dressings, sugar substitutes, and medications.

Dairy products can be consumed depending on individual tolerance. Most persons with lactase nonpersistence can consume milk without the development of symptoms, particularly if small portions of milk (4 fl oz to 6 fl oz) or lactose-containing foods are eaten at separate times during the day. The ingestion of solid food with lactose-containing beverages modifies lactose malabsorption.2 Food solids delay gastric emptying and/or provide endogenous lactase additional time to digest lactose.2.3 Cocoa and chocolate milk have a suppressive effect on human lactose intolerance as evidenced by significantly lowered mean breath hydrogen, bloating, and cramping.


ProductLactose (g)
Milk (1 cup) 
1% and 2% low-fat9-13
Sweetened, condensed30
Yogurt, low-fat (1 cup)11-15
Cottage cheese (1 cup)5-8
Pasteurized processed cheese food (1 oz)0.5-2
Other cheeses (1 oz)0.4-0.8
Icecream (lcup)9
Icemilk (1 cup)10
Sherbet, orange (1 cup)4
Half and half, light cream, whipped cream topping (1 tbsp)0.5
Sourcream (ltbsp)<1

Lactose-reduced dairy products are available and are suitable substitutions for conventional lactose-containing products. Commercial products are available with varying degrees of lactose reduction. A 50% level of lactose reduction may be adequate to relieve signs and symptoms of milk intolerance in the majority of healthy adults with lactose malabsorption.5 Individuals may choose to use onventional dairy products and reduce the lactose levels themselves with commercially available, lactase enzyme drops or tablets. It has been suggested that yogurt is as effective as hydrolyzed lactose milk in alleviating symptoms of lactose intolerance.6 Lactase activity in yogurt may vary across brands.7 Yogurt that has endogenous cultures added post-pasteurization has more lactase activity.

Adding complex carbohydrates or soluble fiber may alleviate symptoms that originate in the small bowel.’ The ingestion of milk with food and fiber components in the diet has been shown to improve symptoms of lactose intolerance.2 Dietary treatment for lactose intolerance in children incorporates some of the same recommendations as those made for adults. Specialized lactose-reduced products, as well as cultured and fermented dairy products, may be used in varying degrees for lactose-intolerant children. Ingestion of lactose- containing foods with solid food and fiber-containing food is recommended.

Infants with primary lactose intolerance should be managed with lactose-free, soy-based formulas or hydrolysate formulas if they are allergic to intact protein.8 Management of secondary lactose ntolerance is variable; well-nourished infants with nondehydrating gastroenteritis may be managed safely with diluted or even full-strength cow’s milk formula after initial rehydration with a glucose-electrolyte solution.8

Related Physiology Primary lactase deficiency, a condition where the lactase enzyme activity level falls post weaning, is a common development with aging. It is most commonly seen in African Americans, Hispanics, Native Americans, Asians, and people of Jewish descent. Adult lactase deficiency is the most common of all enzyme deficiencies; well over half the world’s adults are lactose intolerant .9 Secondary lactase deficiency can be attributed to mucosal injury from a condition or disease process such as regional enteritis, ulcerative colitis, Crohn’s disease, gluten-induced enteropathy, and parasitic infections, or following antibiotic therapy and surgical procedures including gastrectomy, extensive bowel resection, and gastric bypass.


BeveragesAll beverages with allowed ingredients, soybean milks, other lactose-free supplements, lactose-hydrolyzed milkMilk, milk products, or acidophilus milk as tolerance dictates
Breads and cerealsWhole-grain or enriched breads and cerealsDepending on tolerance, some breads and cereals prepared with milk or milk products may need to be avoided
DessertsCakes, cookies, pies; flavored gelatin desserts; water ices made with allowed foodsAny prepared with milk or milk products (eg, sherbet, ice cream, ice milk, custard, pudding, commercial desserts, and mixes)
FatsButter or margarine; salad dressings; nondairy creamer; all oilsAny prepared with lactose-containing ingredients
FruitsAll fruits and juicesNone
Meats and meat substitutesAll meats, poultry; fish; eggs; peanut butter; dried peas and beans; hard, aged, and processed cheese, if tolerated yogurt as toleratedCold cuts and frankfurters that contain lactose filler; cottage cheese
Potatoes and potato substitutesPotatoes; enriched rice; barley; noodles, spaghetti, macaroni, and other pastasPotatoes or substitutes prepared with milk or milk products; mixes prepared with lactose-containing ingredients
SoupsBroth, bouillon; soups made with allowed ingredientsSoups made wit milk or milk products
SweetsSugar; corn syrup; pure maple syrup; honey; jellies, jams; pure sugar candies; marshmallowsChocolate; caramels; any candies made with lactose containing ingredients
VegetablesAllVegetables prepared with milk or milk products
MiscellaneousAll spices, seasonings, flavoringAny prepared with milk or milk products

Lactose tolerance is variable; if an individual is asymptomatic, no restrictions are indicated, If an individual experiences adverse reactions to lactose, following a lactose-controlled diet is advisable. Symptoms associated with lactose intolerance usually subside within 3 to 5 days on a lactose- controlled diet.

Individuals can often identify discomfort associated with digesting lactose; however, true lactase deficiency can be diagnosed clinically with a breath hydrogen test. The breath hydrogen test measures hydrogen produced by colonic bacteria in the presence of unabsorbed sugars.

Adequacy Depending on individual choices, the diet can provide adequate amounts of all essential nutrients.. When dairy products are limited intake of calcium phosphorus, vitamins A and D, and riboflavin may be deficient. Use of dairy products within individual tolerance level and/or use of lactose hydrolyzed milk and milk products could satisfy these nutrient needs. Calcium supplementation is indicated if the diet does not provide adequate calcium.

Gastric Bypass Complications: B1 Deficiency

Thiamine (Vitamin B1) Thiamine, also spelled thiamin, is a water-soluble vitamin found in such foods as yeast, cereal grains, legumes, peas, nuts, port, and beef. This vitamin is essential to a number of metabolic processes, especially in the processing of carbohydrates.

The normal minimal daily requirement of thiamine is 1.4 mg. This amount of vitamin is usually readily obtained from a normal diet. However after gastric bypass, especially in the early post op period, it may be difficult to eat enough food to get enough of the vitamin. There may also be problems with thiamine absorption in some patients. We therefore recommend a daily multivitamin that contains Thiamine and routine thiamine supplementation.

Childrens’ or adult chewable vitamins are convenient during the first 6 weeks post op. We recommend that the patient take one chewable adult Centrum or chewable Bugs Bunny Complete vitamin twice a day for the first 6 weeks. For the next 6 weeks we still recommend taking the vitamins twice a day, but they may be swallowed or chewed. After the first three months we reduce the vitamin dose to one pill once a day. We also recommend thiamine 100 mg (swallowed) daily for the first three months. (Thiamine is water soluble and excessive thiamine is excreted by the kidneys. Thiamine toxicity has not been described in the medical literature.)

Thiamine deficiency Acute thiamine deficiency was originally recognized in patients who were having significant problems taking foods due to a tight pouch or an ulcer and in patients who failed to take multivitamins. When we became aware of the early symptoms, we started to measure blood thiamine levels more routinely. We began to find patients with mild nonspecific symptoms who were otherwise doing well. We therefore started to recommend routine supplementation early on and monitor blood levels later.

Acute thiamine deficiency appears as a nonspecific syndrome: headache, mental clouding, nausea, malaise, myalgias (muscle aches and pains). As it worsens the patient develops more severe mental changes including depression, amnesia, inability to learn, confabulation (making up stories unintentionally), and hallucinations. Additional neurological problems can appear. These include a wide unstable gait (walking pattern), and motor weakness. Finally some patients develop congestive heart failure and peripheral edema (swelling).

Treatment of thiamin deficiency Treatment of mild thiamin deficiency is simple oral supplementation. Treatment of severe acute thiamine deficiency is done by giving high doses of intravenous thiamine for several days. If the deficiency is recent complete recovery is expected. However if it is severe and chronic with marked mental and motor impairment, complete recovery occurs in only half of the patients. Thiamine deficiency is diagnosed by the history of frequent vomiting and the symptoms listed above. A blood test confirm the diagnosis, but treatment is never delayed because the test can take several days to process.

Monitoring thiamin levels We monitor thiamin levels by measuring whole blood thiamin at 6 weeks, 3 months, 6 months, and one year post op. For the long term, we recommend monitoring thiamin every 6 months. Careful monitoring is important because the onset of thiamin deficiency can be insidious and the effects can be serious and permanent.

Prevention of thiamine deficiency During the first three months after surgery we place all patients on B1 100 mg daily as well as on multivitamins. We have started routine supplementation because we have documented that quite a few patients develop mild to moderate deficiency symptoms early on. Later when patients can eat a broader variety of foods in greater quantity we recommend daily multivitamins and then monitor B1 levels in the blood.

Gastric Bypass Complications: B12 Deficiency

Vitamin B12 (Cyanocobalamin) It is a water-soluble hematopoietic (necessary for manufacture of red blood cells) vitamin occurring in meats and animal products. To be absorbed by the intestine, B12 must combine with intrinsic factor, and its metabolism is interconnected with that of folic acid. The vitamin is necessary for the growth and replication of all body cells and the functioning of the nervous system. Deficiency of vitamin B12 causes pernicious anemia and other forms of megaloblastic anemia, and neurologic lesions.

Vitamin B12 is stored in the liver. A healthy adult has a large reserve supply of B12 available, and B12 levels tend to change slowly.

We recommend that our patients take sublingual B12, 1000 micrograms per week. Sublingual means “under the tongue”. B12 supplements that are swallowed don’t get absorbed well. Sublingual preparations are in a crystalline form and can be absorbed directly into the blood stream through the tissues under the tongue.

Your B12 level can be checked with a blood test. We recommend that your level be tested every six months so that you can be sure that you have enough of this important vitamin.

This domain could be yours! Click to Chat on WhatsApp 💬