Nutritional Deficiency After Gastric Bypass Surgery

Nutritional Deficiencies in Obesity & After Bariatric Surgery

Obesity is defined as Body Mass Index (BMI) greater than 30 and is further classified as grade 1 (BMI 30 to 34.9), grade 2 (BMI 35 to 39.9) and grade 3 (BMI ≥40). It is one of the leading medical issues facing developed countries in modern medicine. Obesity increases the risk for cardiovascular disease, diabetes, hypertension and dyslipidaemia, (high cholesterol). In 1987, Manson et al proved that being overweight (BMI >25) was associated with increased risk of death. In the same year, Donahue et al. found an association between coronary heart disease and central obesity. In addition to the physical toll, mental health disorders are also more prevalent in obesity. A study (n=662) showed that obesity was more common among subjects suffering from depression when compared to subjects with normal BMI. However it is worth noting that most medications used by psychiatrists leads to weight gain.

In terms of US dollars the cost of obesity is high and will continue to increase. In 2008 the US spent an estimated 147 billion dollars on the medical costs of obesity. Bariatric surgery is shown to be effective in reducing weight and modifying the risk factors associated with cardiovascular morbidity. Based on current NIH guidelines, bariatric surgery should be considered for grade 3 obesity or grade 2 obesity with two or more comorbidities that are related to obesity (e.g. diabetes and hypertension). Compared with usual care, bariatric surgery is associated with decreased number of cardiovascular deaths and lower incidence of cardiovascular events in obese adults. Surgery also decreased the risk of developing diabetes when compared to usual care in obese persons. The most dramatic effect of bariatric surgery is weight loss and bariatric surgery has shown to either normalize blood pressure or reduce the need for antihypertensive therapy and the effect seems to correlate with the degree of weight loss. A meta-analysis of 29,000 patients undergoing bariatric surgery, showed that bariatric surgery patients had 50% reduction in mortality, compared to non-surgical controls.

Types of Bariatric Procedures

Bariatric procedures can be divided into two broad categories: restrictive and malabsorptive. Restrictive procedures include the laparoscopically placed adjustable gastric band that forms a small gastric reservoir of about 15ml. The sleeve gastrectomy is a restrictive procedure, which leaves a narrow gastric pouch of about 100 ml, and the Roux-en-Y Gastric Bypass (RYGB) is a combined restrictive and malabsorptive procedure, in which the stomach is divided into a small pouch of about 30 ml. This procedure leaves the majority of the stomach excluded and bypassed by ingested food particles. The gastric pouch connects to a Roux limb of jejunum and this results in food particles bypassing some of the small intestine and decreasing the surface area for digestion and absorption.

Nutritional Deficiency and Obesity

The obesity epidemic in the United States may be viewed as a form of malnutrition with an obvious excess of calories, often supplied in the form of fat and sweetened beverages, but with a limited use of healthy foods. Prior studies clearly demonstrated a link between poverty rates, high fast food restaurant density and difficult access to supermarkets or other sources for fruits and vegetables. Another hypothesis is that obesity is associated with an inflammatory state that results in lower levels of specific nutrients. Studies have been done that may explain the apparent paradox that obese people may already present with micronutrient deficiencies. Vitamin B12 is a common deficiency in obese patients and pre-operative nutritional assessments have found Vitamin B12 deficiencies that vary between 3-11%. Vitamin D deficiency is common in temperate zones and has been seen in obesity, with a reported prevalence ranging up to 60%. BMI can lead to increased or decreased risk of fracture depending on the type of bone. There is some evidence of the association of iron deficiency with obesity and pre-operative assessments have found obese subjects to be iron deficient up to 18 %.

Nutritional Deficiencies after Gastric Bypass


Nutritional deficiencies after bariatric surgery are multifactorial. Patients that are assessed for bariatric procedures are strongly encouraged to lose as much weight as possible prior to their procedure. Hence patients go on low calorie diets to lose weight and therefore are more susceptible to deficiencies of iron, B12 and calcium. Bariatric surgery causes drastic anatomical changes of the digestive tract that alters the normal process of digestion. The capacity of the stomach to hold food and secrete juices that facilitate digestion is reduced. So after RYGB, the capacity of the remnant gastric pouch is only 20 ml and similarly, the surface area for digestion and absorption of food in the small intestine is markedly reduced, depending upon the amount of intestine resected. It is reasonable to presume that such alterations in the gut anatomy will adversely affect nutrient metabolism.

This makes bariatric surgery patients more vulnerable to micronutrient deficiencies and protein energy malnutrition. After surgery the patient is on a liquid only diet for period of 2-4 weeks then this diet is gradually advanced to pureed diet over the next few months. Patients cannot tolerate large quantities of food after surgery and their daily caloric intake during the initial postoperative period typically ranges between 500-900 kcal/day. It is difficult to maintain adequate micronutrient intake on such low caloric diets. Furthermore, postoperative complications like vomiting, obstruction, fistula formation, ulcers and dumping can also prevent adequate nutrition. Small bowel obstruction is a late postoperative complication that can occur following RYGB. The risk is higher with laparoscopic RYGB and the obstruction is usually due to internal hernias. Fistula formation is a common complication of sleeve gastrectomy. A meta-analysis showed that fistula rates in sleeve gastrectomies were up to 2.2% and other studies showed fistula rates ranging from 0 to 20%.

vitamins, pills and tablets

vitamins, pills and tablets

Considering the potential for nutritional deficiencies, patients are routinely asked to take multivitamins, supplemental calcium and iron. Supplementation is especially important for patients undergoing the gastric bypass bariatric procedure. However studies have shown that patient compliance with these supplements is low and therefore it is difficult to maintain adequate nutrition. A study showed that over a 10-year period only 33% of patients were compliant with nutritional supplements. These high rates of non-compliance with supplementation make it even more difficult to treat micronutrient deficiencies.

Thiamine B1

Thiamine deficiencies after gastric bypass can result in weakness, polyneuropathies (a disease affecting peripheral nerves), beriberi, Wernicke’s Encephalopathy (WE), nystagmus and hearing loss. The most serious manifestation of thiamine deficiency is Wernicke’s encephalopathy and the main risk factor identified was persistent vomiting and intravenous administration of glucose without thiamine. Wernicke’s encephalopathy leaves residual neurological defects in the majority of the affected. The prevalence of thiamine deficiency in a study following 318 subjects for 2 years was 18%. In a review of subjects who underwent bariatric surgery and developed Wernicke’s encephalopathy, 95% of the affected patients underwent the gastric bypass.

Vitamin B12

The reported prevalence of B12 deficiency widely varies. Studiesyringes report a prevalence that ranges from 11% to 70% after the bariatric surgery. It is worth mentioning that B12 deficiency is prevalent prior to surgery and can be as high as 18%. B12 is mostly bound to protein in our diet and the prevalence of B12 deficiency increases after surgery for all patients, but it is found to be greatest with RYGB procedures and least with restrictive procedures. Supplementation is recommended, as even with supplementation, vitamin B12 levels in a study were found to be in the lower thirds of the reference range. Supplementation can be oral, intranasal, sublingual or intra muscular. The best evidence of efficacy is for the intramuscular route (regular B12 injections).

Vitamin D

Vitamin D deficiency is quite common in bariatric patients being assessed for surgery. Post operatively it is very difficult to assess the impact of bariatric surgery on vitamin D metabolism. In most studies vitamin D levels increase with aggressive supplemental regimens. However despite improvements in serum levels the prevalence of vitamin D deficiency remains high. In a study of a group of patients’ status post LAGB (Laparoscopic Adjustable Gastric Banding), vitamin D deficiency decreased from 58% to 33% but this was not significant. Gastric bypass leads to bone loss, high PTH and 25(OH) D levels. This can be seen despite supplementation with calcium. Vitamin D deficiency increases risk of hypocalcaemia, bone loss with resulting fractures and even osteomalacia. Acutely hypocalcaemia can be associated with cramps and changes in sensory function, which have been reported after bariatric procedures.


Iron deficiency after gastric bypass is common. A retrospective analysis of 959 subjects status post RYGB found that 51% were deficient in iron. Almost half of the iron deficient subjects (40%) were severely deficient. Meat intolerance is common post gastric bypass and results in the absence of an important source of iron in the diet. The overall low parietal cell mass of the pouch results in hypochlorydia and is thought to be one of the mechanisms that lead to decreased absorption of iron in the gut. Iron is absorbed in the duodenum and thus its removal compromises iron absorption. It has been shown using radiolabelled isotopes that iron absorption worsens after gastric bypass. Iron absorption was measured before and after gastric bypass and was found to be decreased in the latter.


Obesity is a common disease in the USA and globally. The incidence and prevalence of obesity is rapidly increasing. Obesity increases the risk of cardiovascular diseases, diabetes and dyslipidemia. Obesity also leads to poor self-esteem and lack of self-confidence as obese individuals consider or are considered as unattractive. Obesity and its associated health risks have a huge financial burden with the estimated cost around 147 billion dollars in 2008. Obesity is a paradoxical state of malnutrition that consists of excessive caloric intake and micronutrient deficiencies. This state can be partially explained by poor dietary choices and poor access to food rich in nutrients. It is also hypothesized that obesity is a state of inflammation and abnormal micronutrient metabolism that results in deficiencies of iron, b12 and vitamin D. The fact that obese people can have micronutrient deficiencies needs to be recognized. This will allow for increased screening, diagnosis and treatment of micronutrient deficiencies in obese people.

Bariatric surgery is indicated for obese individuals with BMI > 40 or BMI > 35 and two or more co-morbidities that are obesity related. Bariatric surgery has shown to help obese patients lose up to 20-35 % of baseline weight and decrease mortality, incidence of diabetes and adverse cardiovascular events. Post bariatric surgery patients have also been found to have micronutrient deficiencies including iron, b12 and vitamin D. The cause of micronutrient deficiencies in patients who have undergone bariatric surgery is multifactorial. Micronutrient deficiencies after bariatric surgery is a result of pre-existing micronutrient deficiencies severely decreased caloric intakes, surgical complications and perhaps altered post-surgical digestive anatomy.

Micronutrient metabolism in obesity is complex and not completely elucidated. As our understanding of the complex physiology of micronutrient digestion in obesity develops, so will our ability to treat micronutrient deficiencies. Further research needs to be done to address questions like Recommended Dietary Intake (RDI) of micronutrients for obese subject and RDI of micronutrients for post bariatric surgery patients. Also supplementation for micronutrient deficiencies for obese patients and bariatric surgery patients is not evidence based. Currently supplementation for bariatric surgery subjects is higher than RDI but there is little evidence of benefit. One could argue that even higher dose supplementation might still be inadequate. Nutrition in bariatric surgery is challenging. The importance of identifying and treating micronutrient deficiencies prior to surgery is reiterated. After bariatric surgery it is important to maintain close follow up for nutritional status as deficiencies can result in devastating consequences including Wernicke’s encephalopathy, neuropathies and heart failure.

Title: Nutritional Deficiencies in Obesity & After Weight Reduction
Published: Annals of Nutritional Disorders and Therapy 2(2):id1024 (2015)
Authors: Owais Bhatti, Klaus Bielefeldt and Salman Nusrat