Tiffany R. Beckman

Changes in Gastrointestinal Hormones and Leptin after Roux-en-Y Gastric Bypass Procedure: A Review

Roux-en-Y gastric bypass is a well-accepted tool for the treatment of obesity and, compared to conventional weight loss methods (eg, diet and exercise) and other weight loss surgeries (eg, gastric banding), it results in considerable weight loss that is maintained long term. Although successful, the mechanisms for weight loss are not completely understood and it is thought that gastrointestinal hormones play a role. Several gastrointestinal hormones have been identified for their effects on appetite, including glucagon-like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY), leptin, and ghrelin. This review encompasses a literature search that included 45 primary articles and shows that there are alterations in GLP-1, PYY, leptin, and ghrelin postoperatively. GLP-1 and PYY concentrations were usually found to be higher, whereas ghrelin levels were typically lower post- Roux-en-Y gastric bypass than in individuals with obesity, those who were overweight or of normal weight, and in those who underwent procedures other than Roux-en-Y gastric bypass or who achieved weight loss by lifestyle modification. An understanding of how gastrointestinal hormones change after Roux-en-Y gastric bypass may help dietetics practitioners optimize nutrition care for this patient population. A review of the literature also highlighted some research gaps that should be taken into consideration when designing future studies.

Changes in gastrointestinal hormones and leptin after Roux-en-Y gastric bypass surgery.

BACKGROUND Roux-en-Y gastric bypass (RYGB) imparts long-term weight loss, the mechanisms for which are not well understood. Changes in leptin and gastrointestinal (GI) hormones, including glucagon-like peptide 1 (GLP-1), peptide YY (PYY), and ghrelin, may contribute to the relative success of RYGB compared with conventional weight loss methods. This study evaluated changes in GI hormones and leptin post-RYGB. The study also evaluated whether GI hormones differed after a short-term dose of protein or fat. METHODS GLP-1, PYY, ghrelin, and leptin were assessed in 16 women before RYGB and up to 1 year after RYGB. Plasma was collected before and at several times after a short-term equicaloric dose of protein or fat. RESULTS GLP-1 area under the curve (AUC) increased at week 6 and 1 year in the fat beverage (FAT-BEV) group compared with baseline. PYY AUC remained elevated at 1 year in the FAT-BEV group. Ghrelin AUC decreased at week 2, week 6, and 1 year in the protein beverage (PRO-BEV) group compared with baseline. Ghrelin AUC was lower in the PRO-BEV group compared with the FAT-BEV group at week 6. Fasted leptin decreased at all visits in both groups and was lower in the FAT-BEV group compared with the PRO-BEV group at 1 year. CONCLUSIONS Changes from baseline were evident for all GI hormones and leptin; some differences were evident soon after surgery (ghrelin, leptin), whereas others were maintained long term (GLP-1, PYY, ghrelin, leptin). In response to a short-term stimulus, protein suppressed ghrelin and fat potently stimulated GLP-1 and PYY. Future work in this area is warranted.

Predicting energy expenditure in extremely obese women.

BACKGROUND The most common clinical method for resting energy expenditure (REE) assessment is prediction equations. The purpose of this study was to elucidate which prediction equation is most accurate for REE assessment in extremely obese women. METHODS Fourteen extremely obese women (mean +/- SD body mass index: 49.8 +/- 6.2 kg/m(2); age: 49 +/- 10 years) were measured for height and weight and REE via indirect calorimetry (IC) by a metabolic cart system. Predicted REE was evaluated by several equations, including Harris-Benedict with actual body weight, Harris-Benedict with several adjustments to body weight, Cunningham, Mifflin-St Jeor, Owen, World Health Organization (WHO), and Bernstein equations. Accuracy was determined by mean difference data (IC REE - equation REE; Students paired t-test), correlation coefficients, and agreement between methods by Bland-Altman plots. Accuracy was also evaluated on an individual basis, defined by the percentage of individuals within +/-10% of IC REE. RESULTS The Mifflin-St Jeor, Harris-Benedict with actual body weight, and the WHO equations were the most accurate in terms of mean predicted REE. The mean predicted REE values by all other equations were different from the IC REE values (p < .1). According to the individual data, the Mifflin-St Jeor was most accurate (14% outside +/-10% IC REE). The Harris-Benedict with actual body weight and WHO equations were less accurate on individual terms, with 29% and 42% of the predicted REE values, respectively, falling outside +/-10% of IC REE. CONCLUSIONS The Mifflin-St Jeor equation was most accurate method for REE assessment in extremely obese women.

Multifrequency bioelectrical impedance analysis and bioimpedance spectroscopy for monitoring fluid and body cell mass changes after gastric bypass surgery.

BACKGROUND & AIMS There is a growing need for clinically applicable body composition assessment tools for extremely obese individuals. The objective of this research was to evaluate several bioimpedance techniques for monitoring changes in fluid, particularly intracellular water (reflecting body cell mass) after bariatric surgery. DESIGN Fifteen extremely obese women (body mass index: 48.9+/-7.0 kg/m(2); age: 48+/-9 years) were assessed before (baseline; T1), and approximately 6 weeks after gastric bypass surgery (T2) by several multifrequency bioelectrical impedance analysis approaches (MFBIA; QuadScan 4000), a bioimpedance spectroscopy device (BIS; Hydra 4200), and multiple dilution. RESULTS BIS provided intracellular water estimates that were comparable to criterion, based on mean comparisons, at both time points (T1: criterion: 24.2+/-3.1L, BIS: 24.0+/-3.7 L; T2: criterion: 20.6+/-3.7 L, BIS: 19.7+/-3.2L). MFBIA (with Deurenberg equations) provided comparable measures to criterion only at T2 (criterion: 20.3+/-3.7L, MFBIA: 20.6+/-2.7 L). Both MFBIA (with QuadScan proprietary equations) and BIS produced estimates of intracellular water change that were comparable to dilution. There was substantial variability in individual volume measures. CONCLUSIONS Although MFBIA and BIS hold promise as convenient techniques for assessing fluid changes, individual variability in measurements makes them impractical for assessment of extremely obese patients in the clinical setting.

Comparison of DXA and water measurements of body fat following gastric bypass surgery and a physiological model of body water, fat, and muscle composition

Measurement of body composition changes following bariatric surgery is complicated because of the difficulty of measuring body fat in highly obese individuals that have increased photon absorption and are too large for the standard dual-energy X-ray absorptiometry (DXA) table. We reproducibly measured body composition from half-body DXA scans and compared the values of total body fat estimated from total body water (TBW) and DXA measurements before and after Roux-en-Y gastric bypass surgery (RYGB). DXA, TBW (deuterium dilution), extracellular water (ECW; bromide dilution), and intracellular water (ICW) measurement (by subtraction) were made before surgery and at 2 wk, 6 wk, 6 mo, and 12 mo after surgery. Twenty individuals completed baseline and at least four follow-up visits. DXA appeared to underestimate the fat and bone mass in extreme obesity (before surgery), whereas at 6 and 12 mo after surgery, the DXA and TBW fat measurements were similar. The ECW-to-ICW ratio was increased in obese individuals and increased slightly more after surgery. We describe a new model that explains this abnormal water composition in terms of the normal physiological changes that occur in body composition in obesity and weight loss. This model is also used to predict the muscle mass loss following RYGB.

Amygdalar opioids modulate hypothalamic melanocortin-induced anorexia.

We wanted to assess the possibility that opioid activity in the central amygdala (CeA) could modulate the feeding inhibition of melanocortin stimulation of the paraventricular hypothalamus (PVN). The melanocortin system is important in both the acute regulation of satiety and feeding behavior and in the integration of long-term appetite signals. Melanotan II (MTII) is a synthetic MC3R and MC4R agonist which reduces food intake when given intracerebroventricularly (ICV) and into the PVN. Tyr-D-Ala-Gly-(me) Phe-Gly-ol (DAMGO), a micro-opioid receptor agonist, increases food intake, while opioid antagonists, like naltrexone (NTX), inhibit food intake after injection into many brain sites involved in appetite regulation, including the CeA. In food-deprived male Sprague-Dawley rats, co-injected intra-PVN MTII partially blocked the orexigenic effect of co-injected intra-CeA DAMGO. Intra-CeA NTX co-injected with intra-PVN MTII reduced food intake significantly more than either alone. NTX administered intra-CeA reduced c-Fos-immunoreactivity (IR) in nucleus accumbens neurons significantly compared to the intra-PVN MTII treated animals, animals co-injected intra-PVN with MTII and intra-CeA with NTX animals, and control animals. Intra-PVN MTII induced c-Fos-IR in significantly more PVN neurons than observed in control animals. Intra-CeA NTX co-injected with intra-PVN MTII induced c-Fos-IR significantly in PVN neurons relative to control and intra-CeA NTX animals. Such data support the significance of opioid action within the CeA as a modulator of the feeding regulation action of melanocortins within the PVN, occurring within the context of a larger appetitive network.

Comparison of Handheld to Metabolic Cart Indirect Calorimetry for Resting Energy Expenditure Assessment in Extremely Obese Women

Resting energy expenditure (REE) was measured by a Deltatrac (DT) metabolic cart and a MedGem (MG) handheld indirect calorimetry device in 14 extremely obese women. DT and MG REE measures were compared by Students paired t test, correlation, and Bland-Altman plots. MG accuracy was also evaluated in comparison to DT by individual data inspection. DT and MG REE values were different on the basis of mean data. MG REE values were outside ±10% of DT REE in 6 of 14 subjects. It may be concluded from these data that the MG device may be unacceptable for clinical measurement of REE in this population.