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Topics in Clinical Nutrition:
doi: 10.1097/01.TIN.0000443024.21277.0f
Weight Management

Body Composition Changes and Reduction of Risk for Metabolic Syndrome After Bariatric Surgery: Implications for the Registered Dietitian

Baudino-Burgarello, Erin MS, RD, LD; Cohen, Deborah DCN, RD; Cerami, Jean MS, RD, LD; Conn, Carole A. PhD, RD, CSSD, LD, FACSM

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Author Information

Lovelace Westside Hospital, Albuquerque, New Mexico (Ms Baudino-Burgarello); and Nutrition and Dietetics Program (Dr Cohen), Dietetic Internship (Ms Cerami), and Nutrition and Dietetics Program (Dr Conn), University of New Mexico, Albuquerque, New Mexico.

Correspondence: Erin Baudino-Burgarello, MS, RD, LD, 10501 Golf Course Rd NW, Albuquerque, NM 87114 (etbmail@gmail.com).

The authors have disclosed that they have no signifi-cant relationships with, or financial interest in, any commercial companies pertaining to this article.

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Abstract

Assessment of body composition after bariatric surgery is important for monitoring the changes that occur with respect to lean body mass and fat (subcutaneous and visceral adipose tissue). Different procedures (malabsorptive vs restrictive) result in different rates and amounts of lean body mass and adipose tissue loss during the short-term and long-term periods after bariatric surgery. Many of the methods used to assess body composition changes are either impractical or not validated for use in the obese and superobese population. Thus, health care professionals should understand the alterations in body composition changes that occur and be able to educate clients accordingly.

SIXTY-EIGHT percent of Americans are considered overweight or obese and 33.8% are classified as obese.1 Overweight is defined as a body mass index (BMI) of 25 to 29.9, obese as a BMI of 30 to 39.9, and morbidly (severely) obese as a BMI of 40 or more. Bariatric surgery is becoming more common as a tool to achieve weight loss in obese and morbidly obese individuals. Bariatric surgery results in weight loss (both adipose and lean tissue) and body composition changes, which help to reduce the risk of developing chronic disease including cardiovascular disease, metabolic syndrome (Met S), type 2 diabetes, hypertension, and stroke. Assessment of BMI, body composition, distribution of body fat, and total body weight after bariatric surgery are important tools when evaluating one's risk for the development of chronic disease. However, a major limitation to using BMI to assess weight after bariatric surgery is that it does not discriminate between fat and lean tissue; therefore, assessment of body composition may be a more important tool. The objectives of this article are (1) to describe the use of body composition assessment following bariatric surgery, (2) to elucidate methods used in the clinical setting to assess body composition, and (3) to discuss nutritional counseling as a tool in maximizing fat loss and minimizing loss of lean body mass (LBM) after bariatric surgery.

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BODY COMPOSITION ASSESSMENT

Body composition describes the structural components of the body (bones, tendons, skeletal muscle, visceral, adipose tissue, and minerals). These structural components can be classified into lean and fat mass (FM).2 Fat is the largest energy reserve and is stored as triglycerides in adipose tissue either under the skin (subcutaneous) or around the major organs (visceral). Ectopic fat is the deposition of triglycerides within cells of nonadipose tissues, such as muscle tissue or blood vessels, that usually contain only a small amount of fat.3 Lean mass is the amount of body mass that is not fat and comprises mainly water, structural proteins, connective tissue, and minerals.2 A large amount of fat stored in the abdominal cavity, or visceral fat, is associated with a greater risk for Met S.4 Fifty percent of body fat is subcutaneous fat and only 7% to 15% of body fat is visceral adipose tissue in healthy weight individuals.4,5 Abdominal fat can be estimated by measuring waist circumference (WC), but more accurate measurements are obtained by imaging technologies, which can differentiate between subcutaneous and visceral abdominal adipose tissue.

Abdominal obesity is one of the components of Met S. The International Diabetes Federation defines Met S as central obesity (defined as WC, with ethnicity-specific values) WC at or above 102 cm for males and 88 cm for females, plus any 2 of 4 additional factors: elevated triglyceride level (>150 mg/dL), reduced high-density lipoprotein cholesterol (<40 mg/dL in males and <50 mg/dL in females), elevated blood pressure (BP) (systolic BP ≥130 mm Hg or diastolic BP ≥85 mm Hg), or an elevated fasting plasma glucose (>100 mg/dL, or previously diagnosed with type 2 diabetes) (Table).5 Other organizations define Met S differently; however, the primary risk factors of triglycerides, high-density lipoprotein cholesterol, BP, and plasma glucose are the same.

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Factors that influence visceral adiposity include genetics, physical activity, and environmental influences (such as sedentary lifestyle, excess caloric intake, or increased intake of saturated fats).5 It is well known that those who have abdominal obesity are at an increased risk of developing dyslipidemia, cardiovascular disease, and type 2 diabetes. The low-grade inflammation that is associated with obesity, particularly with abdominal obesity, is the primary risk factor for the development of comorbid conditions and Met S.6 Bariatric surgery is one intervention used for the treatment of Met S. Weight loss using physical activity and dietary modifications (such as caloric restriction) has been shown to fail in the long term for morbidly obese individuals, with a high incidence of weight regain (83%) in those with morbid obesity.7,8 Currently, bariatric surgery is the only weight loss method proven to be effective in the severely obese population over a long-term period.8 In the United States, the use of bariatric surgery for weight loss has continued to increase from 13 886 surgical procedures performed in 1998 to 220 000 surgical procedures performed in 2008.1 During the last decade, the safety of the operation has vastly improved and is one reason contributing to the increase of 1584% in surgical procedures from 1998 to 2008.1 Many have shown improvements in obesity-related health problems including type 2 diabetes, coronary artery disease, Met S, and hypertension.1,8–11

Studies have shown that patients who were able to obtain a greater weight loss after bariatric surgery also had a significant decrease in Met S comorbidities when more visceral fat was lost compared with diet alone.10 A 95.6% resolution of Met S is expected following bariatric procedures.8

The assessment and monitoring of body composition changes after bariatric surgery allow the registered dietitian to appropriately assess a patient's LBM and risk of Met S. Knowing the patterns of weight loss following bariatric surgery can aid in providing the patient with accurate recommendations for protein and exercise to decrease the rate of LBM loss and monitor the rate of fat loss as correlated with the risk of Met S.

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OVERVIEW OF BARIATRIC PROCEDURES

The 2 most common bariatric surgery procedures are Roux-en-Y gastric bypass (RYGB) and laparoscopic adjustable gastric banding (LAGB). Other bariatric procedures include biliopancreatic diversion and biliointeric bypass (BIBP) and vertical sleeve gastrectomy. All are restrictive procedures in which the size of the stomach is significantly reduced, creating a small pouch and decreasing the amount of food an individual can eat at one time. RYGB is also malabsorptive, where it limits the amount of nutrients that are absorbed. The LAGB is the least invasive of all bariatric procedures. Gastric banding facilitates weight loss by limiting food intake after the placement of an inflatable band around the stomach, just below the gastroesophageal junction, allowing adjustment to the size of the stomach opening by the addition or removal of saline through a subcutaneous port.1 One of the major advantages of the LAGB is the ability to adjust the band for pregnancy or illness when an individual has increased nutrient needs. The band can also be adjusted as weight loss occurs. A disadvantage of the LAGB includes a slower rate of initial weight loss than other bariatric procedures.12 Another restrictive procedure is the vertical sleeve gastrectomy, also known as the sleeve. Removing a majority of the stomach, which may also decrease the amount of ghrelin secreted because a majority of the stomach is removed, creates a vertical sleeve.1 The disadvantages of the sleeve is that it is not reversible.

Roux-en-Y gastric bypass is the most frequently performed weight loss surgery in the United States and is considered the procedure of choice for weight loss.1 The RYGB procedure involves creation of a small stomach pouch to restrict food intake, and a portion of the jejunum is attached to the pouch to allow food to bypass the distal stomach, duodenum, and proximal jejunum.13 A small pouch is created, reducing the stomach to 10% of its former size. Food is then directed from the pouch into the small intestine and bypasses 90% of the stomach and the first part of the intestine.1 Weight loss with the RYGB is successful because it limits food intake and decreases calorie and nutrient absorption. The major benefits of the RYGB procedure include rapid initial weight loss, higher total average weight loss than other bariatric procedures, and less weight regain.12 Disadvantages include dumping syndrome and vitamin and mineral deficiencies. Dumping syndrome is a condition where food travels into the intestines too quickly, which causes nausea, cramping, diarrhea, and dizziness.1 Since a major portion of the stomach and proximal part of the intestine are bypassed, digestion of simple carbohydrates may be hindered, causing dumping syndrome, or limited absorption of nutrients, specifically vitamin B12, iron, vitamin D, folate, calcium, and zinc.14 BIBP is similar to RYGB procedure in that it is both restrictive and malabsorptive; however, a large portion of the stomach is removed, producing a gastric sleeve that is attached to a small portion of the duodenum. There is considerable amount of weight loss with this procedure (∼70% of excess body weight); however, the risk of complications is high due to the limited availability of nutrients.1

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BODY COMPOSITION CHANGES AFTER WEIGHT LOSS

Weight reduction regimens should strive to result in a loss of visceral and subcutaneous adipose tissue and to minimize LBM loss to improve health and reduce risk of chronic disease. Assessment of changes in body fat quantity and distribution needs to be an integral part of the health care professional's arsenal to monitor overall weight loss and improvements in metabolic and cardiovascular risk.

Weight loss amounts and rates vary depending on what type of bariatric procedure is performed. After 1 year, the average weight loss is 25.0 kg (55 lb) and 36.0 kg (79.2 lb) for LAGB and RYGB, respectively.10 The most significant amount of weight loss, of all bariatric procedures, typically occurs during the initial phase (0–6 mo postoperation). After the initial phase, LBM is maintained and FM loss continues at a steady state.10 Long-term outcomes (>5 y), such as improvements in BMI, and percent excess weight loss (% EWL), are not similar in individuals undergoing LAGB and RYGB.

Spivak et al15 found significant differences in BMI and %EWL between those undergoing LAGB and RYGB. In this retrospective long-term (>5 y) study, outcome (BMI, EWL, and failure rate) results were compared between obese individuals who underwent either the LAGB (n = 127) or RYGB (n = 105) procedures. Failure rate was defined as poor weight loss and requirement of band removal.15 The long-term outcomes in the RYGB group were significantly better than those in the LAGB group (P < .05). The RYGB had a reduction of 15 kg/m2 BMI and 80% EWL. The LAGB group reduced its BMI by 9 kg/m2 and maintained a long-term %EWL of slightly more than 40%, but this was not statistically significant. The main limitation identified by the investigators of this study was that the subjects in the LAGB group had a 50% failure rate in the long term attributed to the removal of their band or poor weight loss. As the authors stated, there is a concern that LAGB should not be offered to patients if there is a high chance of a failure rate in 5 to 10 years. RYGB demonstrated persistent and significantly better weight loss and lower failure rates than the LAGB throughout a long-term follow-up period.15 This difference could possibly be attributed to the fact that the Roux-en-Y is a permanent surgical procedure that results in both restriction and malabsorption.

Monitoring body composition changes during the postoperative period is important to evaluate risk for Met S and other obesity comorbidities so that appropriate adjustments in diet, physical activity, and behaviors can be made to improve overall weight loss and health. Monitoring body composition may assist in minimizing loss of LBM, especially in the initial postoperative period, because those who undergo RYGB are at risk for larger losses of LBM, which can have negative effects on physical functions, such as activities of daily living, strength, and possibly energy expenditure.

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BODY COMPOSITION TECHNIQUES

Body composition can be measured using a variety of techniques such as dual-energy x-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA), magnetic resonance imaging (MRI), skinfolds, underwater weighing, and air displacement plethysmography. In the obese and overweight individual, each method has its limitations.

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Bioelectrical impedance analysis

Bioelectrical impedance analysis is based on the body's electrical conductivity, in which relative to water, lean tissue's electrolyte content has higher electrical conductivity and lower impedance than fatty tissue.4 Body composition is assessed in 1 of 3 ways: upper body, lower body, or segmental BIA. Upper and lower body BIA assessment tools measure upper or lower extremity fat and fat-free mass and do not measure the FM in the abdominal area. Segmental analysis views the body as 5 separate cylinders where the abdomen and each arm and leg are measured individually and then whole body volumes can be predicted from the sum of these values.16

Bioelectrical impedance analysis equipment available in most clinical settings includes InBody (4-compartment method measuring upper and lower body but excludes abdominal section), RJL systems (electrodes placed at the hand and the foot), and hand-held and foot-to-foot systems. Bioelectrical impedance analysis is an attractive option for assessing body composition in the clinical setting because of its relative portability, ease of use, low cost, and safety. However, there are limitations. Bioelectrical impedance analysis is affected by sex, age, hydration, physical activity, certain medications, and hormonal variation including the menstrual cycle, race, ethnicity, and level of fatness.17 In the morbidly obese population, BIA is considered unreliable for body composition assessment because BIA devices tend to overestimate fat-free mass and underestimate FM, and the upper and lower assessments do not include abdominal adiposity in their measurement of body composition.18,19

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Skinfold measurements

The skinfold or fat-fold thickness measurement is based on total body fat estimates and on the assumption that 50% of body fat is subcutaneous fat.4 Accuracy decreases with increasing obesity. Sites that are measured using skinfold calipers include abdomen, biceps, calf, forearm, midaxillary, subscapular, suprailiac, triceps, and thigh in both men and women.20 The majority of national reference standards and methods of evaluation are available for the triceps skinfold and subscapular area; therefore, these areas are most useful when doing skinfold measurements.4,21

Few clinicians are adequately trained or may not have calibrated skinfold calipers. In addition, skinfold measurements assess only the area being measured, and thus, a minimum of 3 to 5 measurements from the abdomen, biceps, chest, calf, forearm, midaxillary, subscapular, suprailiac, triceps, and thigh need to be obtained to get an accurate assessment of the entire body because of varied body distribution patterns. Using skinfolds to assess body fat is less than ideal in the obese population, because it is not possible to measure significant skinfold thickness because of the inadequate size of the calipers.20 While skinfold assessments are an inexpensive method, inaccuracy of measurements, especially in the morbidly obese population, limits its practicality. Body fat measured using skinfold equations and BIA tend to underestimate the amount of body fat when compared with underwater weighing.

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Underwater weighing

Underwater weighing is considered the criterion standard for body composition measurement and is based on the principle that the volume of an object submerged in water equals the volume of water the object displaces. Once the volume and mass are known, the density can be calculated.4 While underwater weighing is considered the criterion standard, it is not always a practical approach to assess body composition in the morbidly obese. Underwater weighing requires significant training, equipment is not easily accessible, and participants must be submerged underwater and stay under for a considerable length of time for the measurement to be made. In the obese population, this can be an uncomfortable measurement tool since they may not be comfortable in a bathing suit or proper equipment may not be available to accommodate their body size. Underwater weighing is currently limited to research facilities.

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Imaging techniques

Imaging, including MRI, computed tomography (CT), and DXA, is the most accurate method for the measurement of body composition. Imaging methods provide an accurate assessment of the spatial distribution of adipose tissue by distinguishing the different tissue types and organs, as seen in CT and MRI.22 Magnetic resonance imaging and CT provide a 3-dimensional high-resolution anatomical data set, where quantifying the distribution of adipose tissue throughout the body can determine the patient's cardiovascular risk.17,22 Dual-energy x-ray absorptiometry estimates whole body and regional estimates of bone mineral, bone-free fat-free mass (FFM), and FM.17

Exposure to radiation is a major limitation of using CT and DXA for body composition assessment, which is a particular concern for the pediatric population, those who are pregnant, and for obtaining serial measurements (such as in longitudinal studies). Magnetic resonance imaging, on the contrary, has the ability to distinguish between ectopic fat, adipose, and nonadipose tissue through the higher contrast images produced by the MRI scanner. Magnetic resonance images depend on differences in proton density within the different tissue types, providing an image with characteristic differences in intensities, where fat appears brighter and water appears darker. The high contrast that MR image provides allows for further discrimination between 2 tissue types, such as between adipose and lean tissue and improved estimates of ectopic fat.22 Improved estimates of ectopic fat further help with the assessment of central obesity and, therefore, for Met S risk assessment. Magnetic resonance imaging does not expose individuals to ionizing radiation, like CT and DXA, and, therefore, MRI can be useful in longitudinal studies and is relatively safe when assessing body composition in children and women of childbearing age.22 Both MRI and CT are expensive (∼$500 per scan), and availability of equipment may be limited. Computed tomographic scanners are typically used in research but not in the clinical setting. Magnetic resonance imaging, DXA, and CT scanners have weight and length limitations and are unable to accommodate very large persons (BMI >40 kg/m2), or more than 440 lb typically.17,22

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Dual-energy x-ray absorptiometry

Dual-energy x-ray absorptiometry is currently the criterion standard technique for the assessment of bone mineral density and the diagnosis of osteopenia and osteoporosis. A DXA system also provides whole-body and regional estimates of bone-free FFM and FM, and is, therefore, emerging as a technique to assess body composition. Dual-energy x-ray absorptiometry scans provide a reasonable estimate of total and regional (trunk, legs, and arms) fat and FFM in vivo.10,22 Radiation exposure from a DXA scan is considerably lower than that from a CT scan and, therefore, can be used to monitor body composition changes after a bariatric procedure. Dual-energy x-ray absorptiometry also provides reliable accuracy and reproducibility, providing for the assessment of regional body composition and nutritional status in disease states and growth disorders. Compared with MRI and CT, DXA does have a relatively lower cost and has more widespread availability; however, there are limitations. First, DXA is unable to distinguish between, or is unable to compare amounts or changes in visceral versus subcutaneous fat, or quantify types of fat in specific body compartments such as the abdomen.22 In addition, many scanning beds have an upper weight limit (160 kg/350 lb.) and, therefore, the whole-body field of view cannot accommodate larger individuals. Dual-energy x-ray absorptiometry estimates of FM are skewed as an individual's “trunk thickness” increases.17 There is also evidence to suggest that as abdominal thickness increases, DXA underestimates the amount of FM, and this error proportionally increases with increased body fat.10 Under- or overhydration also impacts the estimates of total or lean mass, where it has been estimated that a 5% change in water content of the FFM influences DXA estimates of body fat about 2.5%.22

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Air displacement plethysmography

Air displacement plethysmography measures body density via air displacement and is similar to the principle of hydrostatic weighing except that air is being displaced by volume rather than water.23 Air displacement plethysmography has been shown to be accurate in several population groups including children and those who are handicapped.23 Research on the validity in the obese population is limited. Limitations include accessibility to equipment; size constraints; and in order to be measured, participants must wear a bathing suit and swim cap, which may be uncomfortable or impractical for some obese or morbidly obese individuals.

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Effects of weight loss after bariatric surgery on body composition and Met S

Bariatric procedures are far superior for achieving weight loss compared with traditional weight loss methods in the obese and morbidly obese populations.24 Both restrictive and malabsorptive procedures result in an average weight loss of 61%, often with resolution of type 2 diabetes, reduction in cardiovascular risk factors, and an overall improvement of quality of life.24 Recent research has indicated that there is an increase in % EWL, in addition to changes in LBM and body composition in both the short- and long-term periods after bariatric surgery.

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Body composition postbariatric surgery

Ciangura et al10 examined the changes in total and regional body composition in premenopausal obese females (n = 42) (mean BMI of 44.6 kg/m2 at baseline) after RYGB compared with a control group (nonsurgical group) (n = 48) over a 1-year period. The groups were matched for age and body fatness at baseline. Dual-energy x-ray absorptiometry was used to measure total mass, trunk and appendicular LBM (kg) and FM (kg), bone mineral content, and total body skeletal muscle mass. Dual-energy x-ray absorptiometry scans were obtained at baseline, 3 months, 6 months, and 1 year after surgery. Lean body mass loss reached a plateau at 6 months while FM continued to decrease, and there was a continuous decrease in total FM, body weight, and BMI during the study period in the RYGB group.

Weight loss (LBM and FM) was greatest and the most rapid during months 1 to 3 after surgery (P < .05). One year after RYGB, there was a significant (P < .05) loss in both appendicular and trunk FM, with a mean loss of 14.5 kg and 16.1 kg, respectively. The mean weight loss 1 year after RYGB was 36.0 kg or 29.5% of initial body weight, which was significant (P < .05). The subjects in the surgical group had a decrease in lean muscle (loss of 9.8 ± 4.8 kg) after 1 year (P < .05). This study showed that the RYGB resulted in a significant loss of abdominal fat and that fat loss (P < .05), while most rapid in the first few months after surgery, continues for at least a year and lean mass loss decreases 6 months postoperatively. This has important implications as the results show that RYGB reduces the risk of Met S with improvements in the body composition, especially in a decrease in appendicular fat and total body weight. One limitation of this study was the use of DXA to assess body composition since the validity of DXA in the morbidly obese has not been adequately studied.

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Exercise and LBM after bariatric surgery

Metcalf et al25 investigated the effects of exercise during the postoperative period on 100 participants who underwent the duodenal switch (DS) procedure, which is similar to the RYGB procedure in that it is a malabsorptive and restrictive procedure. The exercise group, who exercised for 30 minutes 3 or more days per week, at any intensity, had an 8% increase in LBM at 18 months.25 The results from this study demonstrate that exercise does minimize the loss of LBM following bariatric surgery. Also, as physical function improves with weight loss after laparoscopic vertical banded gastroplasty (LVBG), it would be beneficial for patients to increase their physical activity program to continue to increase LBM and decrease FM.26 From this study, it could be hypothesized that encouraging patients to initiate an exercise routine of 30 minutes 3 times a week, before surgery, can help with LBM preservation after surgery and should be tested in future work.

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Body composition changes and energy expenditure following bariatric surgery

Changes in body composition can have significant effects on energy expenditure after bariatric surgery and, therefore, have important implications with respect to individual calorie needs. Olbers et al27 set out to examine how different bariatric procedures affect body composition; basal metabolic rate, energy expenditure, and dietary intake. Obese patients (BMI > 30 and <50 kg/m2) were randomized into either the RYGB (n = 37) or LVBG (n = 46) groups and were followed for 1 year after surgery. Body composition was assessed at baseline and at the 1-year follow-up using DXA (bone mineral content, fat, and lean tissue mass) and CT (tissues). Basal metabolic rate was assessed by indirect calorimetry, and diet was assessed using self-reported Food Frequency Questionnaire. The Food Frequency Questionnaire included 49 questions on ordinary foods consumed during 3 months prior to the study (to establish the baseline) and again at 1-year follow-up.

The RYGB group had a larger reduction in weight, BMI, WC, and hip circumference at 1 year postoperatively than those in the RYGB group, although this was not statistically significant.27 There were dramatic reductions in the total fat of those in the RYGB group compared with the subjects in the LVBG group, with a mean loss of 26.9 kg versus 20.2 kg, respectively (P = .005). Truncal fat reduction contributed most to this difference. Computed tomographic scans also showed that the subjects in the RYGB group had a larger reduction of abdominal adipose tissue, but this was proportionally equivalent to the reduction of subcutaneous adipose tissue.27

One-year postoperative, basal metabolic rate changes did not differ significantly between the RYGB and LVBG groups. The mean reductions in energy expenditure were 498 ± 273 kcal and 481 ± 234 kcal (P = .773), respectively; and the reduction of energy intake was 1465 ± 942 and 1087 ± 940 kcal (P = .105), respectively. At 1 year postoperatively, total energy from protein in both groups was about 15% of total calories where the RYGB group consumed more carbohydrates and less fat than the LVGB group. The RYGB group also ate more fruits and vegetables than the LVGP group. This is an important finding for RDs to consider when counseling the bariatric population. Ideally, patients should consume more protein, fruits, vegetables, and healthy fats than simple carbohydrates. Similar to what others have shown,10,26 this study found that a greater weight loss was seen after RYGB than LVBG, in which a large portion of this weight loss was attributed to a reduction in the truncal fat region and a decrease in the sagittal diameter. This study also examined how dietary patterns postsurgery may affect weight loss after bariatric surgery. As the authors explain, previous studies have indicated that restrictive bariatric procedures tend to increase the patient's use of liquid high-calorie diets and encourage the avoidance of foods that are difficult to digest, such as meats and raw vegetables.27

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Nutritional counseling

Patients who present to RDs for nutritional counseling after a bariatric procedure typically experience rapid LBM and FM loss until approximately 6 months postsurgery, where LBM accounts for a significant amount of weight being lost. Because there are few options for assessing body composition in this population, it is important for RDs working with bariatric patients to familiarize themselves with the various patterns of weight loss, body composition changes, and the patterns of peak loss between LBM and FM. Thus, RDs can then provide appropriate nutritional counseling during the 6 months postoperatively to minimize LBM loss. Both restrictive and malabsorptive bariatric procedures have been shown to decrease weight, increase % EWL, and lower BMI. Roux-en-Y gastric bypass is coined the criterion standard because of the higher success rate in reducing the BMI, increasing the % EWL, and reducing excess FM. In the long term of 5 years, studies have shown9,15,25 RYGB with a significantly lower weight, BMI, and greater % EWL. In the short term, LAGB causes slower LBM loss than RYGB. Weight loss secondary to restrictive and malabsorptive procedures does occur at different rates, while both have the most rapid weight loss in the first 6 months, and a majority of LBM is lost in this time. In later years, between years 4 and 7, there is a tendency for weight regain. Both bariatric procedures reduce weight, BMI, and visceral adiposity, and increase % EWL, and, therefore, both procedures have the potential to decrease the risk of Met S.

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Implications for practice

Monitoring body composition changes after bariatric surgery is important for reassessment of LBM and fat loss following bariatric surgery. Changes in fat loss, specifically visceral versus subcutaneous losses, help ascertain risk for Met S. Currently, there is a limited availability in the clinical setting and access to the appropriate equipment for use in the assessment of body composition changes in the obese and morbidly obese populations after bariatric surgery. In addition, there are limited data on the validity and reliability of the equipment clinicians use in this population. Skinfolds and BIA do not account for visceral adiposity: these measurements underestimate FM. Dual-energy x-ray absorptiometry, MRI, and CT, while more accurate, have serious limitations with respect to cost and accessibility, and they have length and weight restrictions and, therefore, have limited practical use in this population. Dietitians need to be cautious when interpreting data obtained from skinfolds and BIA because of the lack of validity and reliability of these measurements in both the obese and morbidly obese populations.

Availability of body composition equipment varies among different facilities. For those in large teaching hospitals, MRI may be more accessible than those practicing in a smaller, community hospital. For those working with individuals who weigh more than 440 lb (200 kg), a valid and reliable method has not yet been identified. A safe, inexpensive, and effective method to use in those obese individuals would be to obtain waist, bicep, and thigh measurements on a regular basis to monitor changes; however, this method would not allow a practitioner to determine whether changes are due to LBM or adipose loss. A DXA scan can be obtained once a patient has achieved a weight of less than 440 lb. For practitioners in smaller, community hospitals, a DXA scan is most likely to be accessible and relatively inexpensive compared with MRI and CT. Dual-energy x-ray absorptiometry scans do provide good accuracy and reproducibility of total and regional (trunk, legs, and arms) fat and FM.10,22

Data from recent studies27 suggest that there are changes in energy expenditure after bariatric surgery. Potential changes in energy expenditure and energy intake should be considered when counseling patients postsurgery. It is important to focus the patient education on emphasizing lean high biological value protein sources in the patient's diet and to encouraging physical activity to help preserve LBM following a bariatric procedure.

Ideally, patients should consume more proteins to preserve LBM and fruits, vegetables, and healthy fats to help preserve micronutrient status. In those patients who undergo the lap band procedure, the small gastric pouch will be able to hold only a half cup of food at each meal, making it increasingly important to emphasize a nutrient dense, high-protein intake. Dietary patterns that are high in carbohydrates, and inadequate in protein, may affect weight loss and adversely affect preservation of LBM. Patients also tend to increase their intake of high-calorie liquids, especially after restrictive procedures and tend to avoid foods that are difficult to tolerate, such as meats and raw vegetables.27

Dietetic professionals need to be aware of potential shifts in eating patterns after restrictive bariatric procedures and focus preoperative nutrition education that emphasizes the importance of fruits and vegetables and high-protein sources in the diet. Although there are no standard recommendations for protein intake after bariatric surgery, many practitioners use 60 to 80 g of protein per day or 1 to 1.5 gm/kg of ideal body weight.28,29 Recommendations for improving tolerance to high-protein foods include teaching the patient to chew the food to applesauce consistency, or mixing foods in a blender to improve tolerance. If meats are difficult to chew, patients should be encouraged to use moist cooking methods (ie, pressure cooker, Crock-Pot, broiling, stewing). Cutting foods into toddler-size bites may also improve tolerance to high-protein foods. Soft, high-protein foods such as eggs, fish, and tofu, and low-fat/low-sugar protein shakes may be tolerated better.

In addition to a high-protein diet, physical activity can also help prevent LBM loss, create muscle, and help minimize skin sagging during loss of FM. Encouraging patients to incorporate an exercise routine of 30 minutes 3 times a week before surgery will help with LBM preservation.30 Preoperative exercise regimens may help improve overall physical function after surgery and should be encouraged in capable individuals. Postoperatively, patients should do light to moderate activity until cleared by their physician, after about 6 weeks, to add resistance training and increase their activity to a moderate level.

While there are few reliable and/or valid methods to assess body composition in this population, dietitians need to be familiar with patterns of body composition alterations that may occur following bariatric procedures. Appropriate nutritional counseling should be applied for optimal health outcomes by monitoring protein intakes and the adherence to physical activity recommendations.

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ectopic fat; lean body mass; subcutaneous adipose tissue; visceral adipose tissue

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