https://orcid.org/0000-0001-7354-4648
Abstract
Alterations in several gastrointestinal hormones are implicated in the postoperative suppression of food intake leading to weight loss after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). The aim was to evaluate changes in responses of gastrointestinal hormones after RYGB and SG and the associations of these changes with weight loss, energy intake, and food preferences.
Forty-two subjects with severe obesity were included (32 RYGB; 10 SG). Postprandial responses of glicentin, oxyntomodulin, glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and ghrelin were measured before and 6 months after surgery. Energy intake and energy density were assessed before and 6 months after surgery using a buffet meal test and weight loss was assessed 18 months after surgery.
Postprandial concentrations of glicentin, oxyntomodulin, GLP-1, and ghrelin differed between RYGB and SG (all P ≤ .02). Enhanced responses of glicentin and oxyntomodulin predicted a greater weight loss (both P < .01) and were associated with a larger decrease in energy density (P ≤ .04). No associations were found for GLP-1, PYY, and ghrelin, and changes were not associated with changes in energy intake. When combing all hormones, 60%, 19%, and 33% of the variations in weight loss, energy intake, and energy density, respectively, could be explained.
Postprandial responses of gastrointestinal hormones differed between RYGB and SG. Enhanced responses of glicentin and oxyntomodulin predicted a better weight loss and were associated with a decreased preference for energy-dense foods. Replication of these results could imply an opportunity to identify patients in need of additional support after surgical treatments of obesity.
Bariatric surgery promotes weight loss through a marked reduction in food intake (1–4). It has been reported that, besides a general suppression of food intake, there may be an additional decrease in energy intake as a result of altered food preferences caused by a more pronounced reduction in intake of high-fat and sweet foods (5–7). Contrary to previous studies, we recently assessed changes in food preferences using a buffet meal test and found no changes in food preferences at the group level (8,9). However, individual changes in food preferences predicted postoperative weight loss (8), indicating that some individuals seem to experience a beneficial shift in food preferences after bariatric surgery. We found that change in energy density of the meal was an especially strong predictor, explaining 39% of the variation in later weight loss. The underlying mechanisms for the altered food preferences remain unclear.
Changes in postprandial responses of gastrointestinal hormones following bariatric surgery have been associated with reduced appetite and food intake (10,11). Enhanced responses of glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and oxyntomodulin and suppressed responses of ghrelin have been linked to reduced food intake in humans (10–16). Furthermore, rodent models have shown an effect of GLP-1 and PYY to reduce preference for high-fat food (17). Increases in postprandial levels of glicentin and oxyntomodulin following bariatric surgery in humans have recently been proposed as predictors of weight loss (18). Among 9 hormones (including GLP-1, PYY, and ghrelin), the authors found changes in glicentin and oxyntomodulin 3 and 6 months after surgery to be the strongest predictors of weight loss. From these findings, the authors hypothesized that oxyntomodulin and glicentin may play important roles in weight regulation, possibly by affecting appetite and food intake (18).
Given that multiple hormones are altered following bariatric surgery, it seems likely that more than 1 hormone alone explains the individual variation in the postoperative reduction in food intake and subsequent weight loss. A combination of several hormones is required, possibly through complex interactions. With studies reporting a greater suppression of food intake from the combined effect of PYY and GLP-1, and PYY and oxyntomodulin than the sum of the single effects of these hormones (12,19,20), targeting multiple receptors involved in appetite regulation may be necessary for the development of improved pharmacotherapy for obesity.
The aims of this exploratory study was (1) to evaluate the responses of glicentin, oxyntomodulin, GLP-1, PYY, and ghrelin in patients after RYGB and SG respectively; (2) to investigate the single and combined associations of these hormones with postoperative weight loss; and (3) to investigate the single and combined associations of these hormones with objectively measured food intake and food preferences.
Materials and Methods
From March 2014 to July 2015, subjects scheduled for RYGB (n = 32) or SG (n = 10) surgery at the Bariatric Clinic, Køge Hospital, Denmark, were recruited. Eligibility for surgery required age ≥ 25 years and body mass index (BMI) ≥ 50 kg/m2 or BMI ≥ 35 kg/m2 with complications of obesity. Furthermore, following national guidelines, a weight loss of ≥8% of initial body weight was required as part of the preparation for surgery. Exclusion criteria included pregnancy, and inability, physically or mentally, to comply with the procedures required by the protocol.
Subjects were examined approximately 3 months before surgery (ie, before initiation of the 8% weight loss), 1–2 weeks before surgery (after the 8% weight loss), and 6 months and 18 months after surgery. At each visit, subjects arrived at the Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark, at 9 am. Anthropometric data were collected and a 954-kJ standardized liquid meal (45% carbohydrate, 41% protein and 14% fat, Cambridge Weight Plan®) was served at 10 am. A second standardized liquid meal (1674 kJ, 120 g of whole milk, 100 g of semiskimmed milk, and 80 g of powder, 39% carbohydrate, 36% protein and 25% fat, Cambridge Weight Plan®) was served at 13:15. The meal was consumed within 20 to 30 minutes. Blood samples were collected and subjective appetite sensations were assessed prior to the meal and 6 times postprandially. An ad libitum buffet meal test assessing total food intake and food preferences was served at 16:30.
A detailed description of the study protocol has previously been published (21). The study was approved by the Scientific Ethics Committees of the Capital Region of Denmark (Journal no. H-3-2013-138) and registered in the database www.clinicaltrials.gov (ID no NCT02070081). All study participants gave written informed consent.
Anthropometric measures
Body weight and height were measured after an overnight fasting period of ~10 hours. Percentage weight loss was defined as the initial weight minus the weight 18 months after surgery, divided by the initial weight, and multiplied by 100.
Biochemical measures
Blood samples were drawn before the meal was served and 15, 30, 60, 90, 120, and 180 minutes postprandially. Blood was drawn into chilled EDTA tubes for total GLP-1, PYY, glicentin and oxyntomodulin (Pefabloc®, 0.1 mg/mL blood was added to the tubes), and total ghrelin. Samples in dry tubes were left to coagulate for 30 minutes before centrifugation, whereas the remaining samples were immediately cooled on ice and centrifuged at 4°C. All samples were frozen at –80°C until analyzed. Plasma concentrations of oxyntomodulin and glicentin were measured as previously described using sandwich enzyme-linked immunosorbent assays (22). Total GLP-1 (sum of 7-36NH2 and 9-36NH2) was measured using radioimmunoassay (antiserum no. 89390), total PYY (sum of PYY1-36 and PYY3-36) using radioimmunoassay (antibodies from Abnova, clone RPY-B12) (23), and total ghrelin using an enzyme-linked immunosorbent assay (Millipore). Only blood samples from 3 months and 1 to 2 weeks before surgery and 6 months after surgery are included in this manuscript.
Energy intake and energy density
Twenty food items were served at an ad libitum buffet meal test: pork rib roast, chicken, fish cakes, nuggets, omelet, French fries, creamy potato gratin, bread, ketchup, remoulade, mayonnaise, skyr (yogurt) with berries, vegetables, cut fruits, vanilla ice cream, chocolate sauce, cocoa meringues, biscuit cones with chocolate, sweet licorice, and Danish pastries. Subjects were instructed to eat according to their preferences and for as long as they wanted. They ate unmonitored and unaccompanied, in order to diminish any social desirability bias. The amount consumed (g) and total energy intake were registered, and energy density of the meal was calculated. Subjects were unaware of this registration (8,9). Energy density of food chosen at the buffet meal was used as a measure of food preferences. This was based on the assumption that a shift in food choice toward healthier and more low-fat food following surgery was approximately reflected by a decrease in energy density. Changes in energy density were found to be a strong predictor of postoperative weight loss (8). Only energy intake and energy density from 3 months before surgery and 6 months after surgery are included in this manuscript.
Statistical analysis
Descriptive data summaries are reported as mean ± standard deviation. Repeated measurements within each surgery type were analyzed using linear mixed models with a visit–time interaction and with within-visit patient-specific random effects. All models were adjusted for age and sex. In case a significant visit–time interaction was found, pairwise comparisons for each time point during the meal test were carried out using post hoc, model-based approximate t-tests. To test for differences in hormone responses between RYGB and SG, linear mixed models with a visit–time group interaction and with within-visit patient-specific random effects were used.
Associations between changes in total area under the curve (AUC) of glicentin, oxyntomodulin, GLP-1, PYY, and ghrelin and percentages weight loss, energy intake and energy density were evaluated using simple linear regression models. In addition, gastrointestinal hormones were also included in the model in relevant combinations to investigate whether combinations of hormones had a more pronounced effect on percentage weight loss, energy intake, and energy density. Moreover, all 5 hormones were included in the same model, to investigate the combined effect of all 5 hormones. AUC was calculated by the trapezoidal rule.
Lastly, to quantify to what extent the effect of relevant hormones on weight loss was mediated through changes in energy intake or energy density of the food consumed at the buffet meal, a mediation analysis was carried out by including energy intake or energy density in linear regression models jointly with the hormone in question (24).
Results are shown as mean ± standard error of the mean (SEM). Graphs are based on raw data and presented as mean ± SEM. P < .05 was considered statistically significant. Statistical analyses were conducted in R version 3.3.2 (25) and figures were produced using GraphPad Prism version 8.0.1.
Results
Forty-two subjects with a mean age of 39.5 ± 9.3 years and a preoperative BMI of 45.0 ± 6.8 kg/m2 were included in the analysis. Two subjects dropped out before the last visit due to pregnancy. These subjects were not included in the linear regression analysis with 18-month weight loss. Thirty-two subjects received RYGB surgery and 10 received SG. Preoperative BMI and age did not differ between RYGB and SG patients (both P ≥ .17). Baseline characteristics are shown in Table 1.
Baseline characteristics of the Roux-en-Y gastric bypass (n = 32) and sleeve gastrectomy patients (n = 10).
| All | RYGB | SG | |
|---|---|---|---|
| Gender (females) | 86% | 84% | 90% |
| Age, y | 39.5 ± 9.3 | 38.3 ± 9.0 | 43.4 ± 9.8 |
| Weight, kg | 130.2 ± 21.5 | 133.2 ± 22.9 | 120.7 ± 12.9* |
| BMI, kg/m2 | 45.0 ± 6.8 | 45.4 ± 7.2 | 43.7 ± 5.2 |
| Diabetes treatment (yes) | 24% | 28% | 10% |
| All | RYGB | SG | |
|---|---|---|---|
| Gender (females) | 86% | 84% | 90% |
| Age, y | 39.5 ± 9.3 | 38.3 ± 9.0 | 43.4 ± 9.8 |
| Weight, kg | 130.2 ± 21.5 | 133.2 ± 22.9 | 120.7 ± 12.9* |
| BMI, kg/m2 | 45.0 ± 6.8 | 45.4 ± 7.2 | 43.7 ± 5.2 |
| Diabetes treatment (yes) | 24% | 28% | 10% |
Data shown as proportion (%) or mean ± SD. *P < .05 for differences between RYGB and SG subjects analyzed by a 2-sample t-test or a chi-square-test (categorical data).
Baseline characteristics of the Roux-en-Y gastric bypass (n = 32) and sleeve gastrectomy patients (n = 10).
| All | RYGB | SG | |
|---|---|---|---|
| Gender (females) | 86% | 84% | 90% |
| Age, y | 39.5 ± 9.3 | 38.3 ± 9.0 | 43.4 ± 9.8 |
| Weight, kg | 130.2 ± 21.5 | 133.2 ± 22.9 | 120.7 ± 12.9* |
| BMI, kg/m2 | 45.0 ± 6.8 | 45.4 ± 7.2 | 43.7 ± 5.2 |
| Diabetes treatment (yes) | 24% | 28% | 10% |
| All | RYGB | SG | |
|---|---|---|---|
| Gender (females) | 86% | 84% | 90% |
| Age, y | 39.5 ± 9.3 | 38.3 ± 9.0 | 43.4 ± 9.8 |
| Weight, kg | 130.2 ± 21.5 | 133.2 ± 22.9 | 120.7 ± 12.9* |
| BMI, kg/m2 | 45.0 ± 6.8 | 45.4 ± 7.2 | 43.7 ± 5.2 |
| Diabetes treatment (yes) | 24% | 28% | 10% |
Data shown as proportion (%) or mean ± SD. *P < .05 for differences between RYGB and SG subjects analyzed by a 2-sample t-test or a chi-square-test (categorical data).
Weight loss 18 months after RYGB and SG surgery was 41.6 ± 1.7 kg (P < .01), with an overall mean percentage weight loss of 32% (Fig. 1). Weight loss was larger in RYGB than in SG subjects (45.6 ± 3.8 kg versus 29.4 ± 5.3 kg, P < .01), and in patients without diabetes than in patients with diabetes (45.6 ± 3.0 kg versus 29.3 ± 5.3kg, P < .01).
Percent weight change 2 weeks before surgery, and 6 weeks, 6 months and 18 months after surgery in both RYGB and SG subjects (▲, black filled line), in RYGB subjects (○, dotted filled line), and in SG subjects (□, black dotted line). Data shown as mean ± SEM. RYGB, Roux-en-Y gastric bypass; SG, sleeve gastrectomy; m and w, months and weeks, respectively.
Changes in gastrointestinal hormones after RYGB and SG
Basal concentrations of glicentin and oxyntomodulin increased after RYGB (P ≤ .03), whereas no changes were found for basal GLP-1 or PYY after RYGB or after SG. Basal concentrations of ghrelin increased after the preoperative diet-induced weight loss (both P ≤ .02) and remained increased after RYGB compared with before the diet-induced weight loss period (P < .01), but decreased after SG surgery (P < .01) (Fig. 2).
Plasma profiles of glicentin, oxyntomodulin, GLP-1, PYY, and ghrelin in RYGB (A–E), and SG patients (F–J), during a 3-hour mixed meal test approximately 3 months before (□, black dotted line), 1–2 weeks before (○, black dotted line) and 6 months after (▲, black filled line) surgery. Raw data shown as mean ± standard error of the mean. P-overall was obtained from a repeated measurement linear mixed model including a visit-time interaction and age and gender as fixed effects and patient as random effect. Time points with differences between visits were identified through model-based pairwise comparisons. Letters indicate P < .05 such that “a” means P < .05 compared with 3 months before surgery and “b” means P < .05 compared with 1 to 2 weeks before surgery. RYGB, Roux-en-Y gastric bypass; SG, sleeve gastrectomy.
Postprandial concentrations of glicentin, oxyntomodulin, GLP-1, and ghrelin differed between RYGB and SG (all P ≤ .02 for the visit–time group interaction), whereas no between-group difference was found for PYY (P = .14 for the visit–time group interaction) (Fig. 2).
Postprandial concentrations of GLP-1 increased after both RYGB and SG (both P < .01 for the visit-time interaction), but were more profoundly increased after RYGB. After RYGB, postprandial concentrations of glicentin, oxyntomodulin, and PYY increased (all P < .01 for the visit-time interaction) but no changes were found after SG (all P ≥ .14 for the visit-time interaction). SG resulted in a marked decrease in ghrelin which remained low throughout the postprandial period (P < .01 for the visit-time interaction) (Fig. 2).
In the RYGB group, postprandial concentrations of glicentin and oxyntomodulin increased more in patients without diabetes compared to patients with diabetes (both P ≥ .02 for the visit time–group interaction). Diabetes status did not affect postprandial concentrations of GLP-1, PYY, and ghrelin (all P ≥ .14 for the visit time–group interaction) (all supplementary material and figures are located in a digital research materials repository (26)).
Changes in gastrointestinal hormones and associations with weight loss
In a pooled analysis of data from both RYGB and SG subjects, increases in AUC for glicentin and AUC for oxyntomodulin at 6 months were associated with percentage weight loss 18 months after surgery (both P < .01), and explained 22% and 21%, respectively, of the variation in weight loss. No association with weight loss was found for GLP-1, PYY, or ghrelin (all P ≥ .25), and changes in postprandial concentrations of the 5 hormones were not associated with weight loss 6 months after surgery (all P ≥ .21) (Table 2).
Associations between change in AUC for glicentin, oxyntomodulin, GLP-1, PYY and ghrelin from pre-weight loss to 6 months after surgery, and percentage weight loss 6 and 18 months after surgery.
| RYGB and SG (n = 42) | RYGB (n = 32) | |||||
|---|---|---|---|---|---|---|
| β±SEMa | R2 | P | β±SEM1 | R2 | P | |
| Weight loss 6 months after surgery | ||||||
| Absolute change in AUC | ||||||
| Glicentin | 0.08 ± 0.10 | 0.02 | .44 | –0.01 ± 0.11 | <0.01 | .92 |
| Oxyntomodulin | 0.24 ± 0.30 | 0.02 | .44 | –0.03 ± 0.34 | <0.01 | .94 |
| GLP-1 | –0.21 ± 0.97 | 0.05 | .83 | –1.34 ± 1.11 | 0.05 | .24 |
| PYY | –0.52 ± 0.63 | 0.02 | .42 | –0.81 ± 0.70 | 0.05 | .26 |
| Ghrelin | 0.03 ± 0.02 | 0.04 | .21 | 0.02 ± 0.03 | 0.02 | .51 |
| Weight loss 18 months after surgery | ||||||
| Absolut change in AUC | ||||||
| Glicentin | 0.50 ± 0.16 | 0.22 | <.01 | 0.41 ± 0.20 | 0.14 | .05 |
| Oxyntomodulin | 1.50 ± 0.50 | 0.21 | <.01 | 1.19 ± 0.63 | 0.13 | .07 |
| GLP-1 | 1.60 ± 1.77 | 0.02 | .37 | –0.56 ± 2.21 | <0.01 | .80 |
| PYY | –0.48 ± 1.20 | <0.01 | .69 | –1.29 ± 1.37 | 0.03 | .36 |
| Ghrelin | 0.05 ± 0.04 | 0.04 | .25 | –0.02 ± 0.06 | 0.01 | .72 |
| RYGB and SG (n = 42) | RYGB (n = 32) | |||||
|---|---|---|---|---|---|---|
| β±SEMa | R2 | P | β±SEM1 | R2 | P | |
| Weight loss 6 months after surgery | ||||||
| Absolute change in AUC | ||||||
| Glicentin | 0.08 ± 0.10 | 0.02 | .44 | –0.01 ± 0.11 | <0.01 | .92 |
| Oxyntomodulin | 0.24 ± 0.30 | 0.02 | .44 | –0.03 ± 0.34 | <0.01 | .94 |
| GLP-1 | –0.21 ± 0.97 | 0.05 | .83 | –1.34 ± 1.11 | 0.05 | .24 |
| PYY | –0.52 ± 0.63 | 0.02 | .42 | –0.81 ± 0.70 | 0.05 | .26 |
| Ghrelin | 0.03 ± 0.02 | 0.04 | .21 | 0.02 ± 0.03 | 0.02 | .51 |
| Weight loss 18 months after surgery | ||||||
| Absolut change in AUC | ||||||
| Glicentin | 0.50 ± 0.16 | 0.22 | <.01 | 0.41 ± 0.20 | 0.14 | .05 |
| Oxyntomodulin | 1.50 ± 0.50 | 0.21 | <.01 | 1.19 ± 0.63 | 0.13 | .07 |
| GLP-1 | 1.60 ± 1.77 | 0.02 | .37 | –0.56 ± 2.21 | <0.01 | .80 |
| PYY | –0.48 ± 1.20 | <0.01 | .69 | –1.29 ± 1.37 | 0.03 | .36 |
| Ghrelin | 0.05 ± 0.04 | 0.04 | .25 | –0.02 ± 0.06 | 0.01 | .72 |
Associations were evaluated using simple linear regression models.
Values in bold represent that the P value is significant (P < 0.05).
aMultiplied by 1000.
Associations between change in AUC for glicentin, oxyntomodulin, GLP-1, PYY and ghrelin from pre-weight loss to 6 months after surgery, and percentage weight loss 6 and 18 months after surgery.
| RYGB and SG (n = 42) | RYGB (n = 32) | |||||
|---|---|---|---|---|---|---|
| β±SEMa | R2 | P | β±SEM1 | R2 | P | |
| Weight loss 6 months after surgery | ||||||
| Absolute change in AUC | ||||||
| Glicentin | 0.08 ± 0.10 | 0.02 | .44 | –0.01 ± 0.11 | <0.01 | .92 |
| Oxyntomodulin | 0.24 ± 0.30 | 0.02 | .44 | –0.03 ± 0.34 | <0.01 | .94 |
| GLP-1 | –0.21 ± 0.97 | 0.05 | .83 | –1.34 ± 1.11 | 0.05 | .24 |
| PYY | –0.52 ± 0.63 | 0.02 | .42 | –0.81 ± 0.70 | 0.05 | .26 |
| Ghrelin | 0.03 ± 0.02 | 0.04 | .21 | 0.02 ± 0.03 | 0.02 | .51 |
| Weight loss 18 months after surgery | ||||||
| Absolut change in AUC | ||||||
| Glicentin | 0.50 ± 0.16 | 0.22 | <.01 | 0.41 ± 0.20 | 0.14 | .05 |
| Oxyntomodulin | 1.50 ± 0.50 | 0.21 | <.01 | 1.19 ± 0.63 | 0.13 | .07 |
| GLP-1 | 1.60 ± 1.77 | 0.02 | .37 | –0.56 ± 2.21 | <0.01 | .80 |
| PYY | –0.48 ± 1.20 | <0.01 | .69 | –1.29 ± 1.37 | 0.03 | .36 |
| Ghrelin | 0.05 ± 0.04 | 0.04 | .25 | –0.02 ± 0.06 | 0.01 | .72 |
| RYGB and SG (n = 42) | RYGB (n = 32) | |||||
|---|---|---|---|---|---|---|
| β±SEMa | R2 | P | β±SEM1 | R2 | P | |
| Weight loss 6 months after surgery | ||||||
| Absolute change in AUC | ||||||
| Glicentin | 0.08 ± 0.10 | 0.02 | .44 | –0.01 ± 0.11 | <0.01 | .92 |
| Oxyntomodulin | 0.24 ± 0.30 | 0.02 | .44 | –0.03 ± 0.34 | <0.01 | .94 |
| GLP-1 | –0.21 ± 0.97 | 0.05 | .83 | –1.34 ± 1.11 | 0.05 | .24 |
| PYY | –0.52 ± 0.63 | 0.02 | .42 | –0.81 ± 0.70 | 0.05 | .26 |
| Ghrelin | 0.03 ± 0.02 | 0.04 | .21 | 0.02 ± 0.03 | 0.02 | .51 |
| Weight loss 18 months after surgery | ||||||
| Absolut change in AUC | ||||||
| Glicentin | 0.50 ± 0.16 | 0.22 | <.01 | 0.41 ± 0.20 | 0.14 | .05 |
| Oxyntomodulin | 1.50 ± 0.50 | 0.21 | <.01 | 1.19 ± 0.63 | 0.13 | .07 |
| GLP-1 | 1.60 ± 1.77 | 0.02 | .37 | –0.56 ± 2.21 | <0.01 | .80 |
| PYY | –0.48 ± 1.20 | <0.01 | .69 | –1.29 ± 1.37 | 0.03 | .36 |
| Ghrelin | 0.05 ± 0.04 | 0.04 | .25 | –0.02 ± 0.06 | 0.01 | .72 |
Associations were evaluated using simple linear regression models.
Values in bold represent that the P value is significant (P < 0.05).
aMultiplied by 1000.
When analyzing only data from RYGB subjects, increases in AUC for glicentin and oxyntomodulin at 6 months were associated weakly and near-significantly with percentage weight loss 18 months after surgery (glicentin: P = .05, R2=0.14; oxyntomodulin: P = .07, R2 = 0.13). No association with weight loss was found for GLP-1, PYY, or ghrelin (all P ≥ .36), and changes in postprandial concentrations of the 5 hormones were not associated with weight loss 6 months after RYGB (all P ≥ .24) (Table 2).
The combined effect of glicentin and PYY, oxyntomodulin and PYY, GLP-1 and PYY or PYY and ghrelin increased the predictive power when compared with the sum of the single effect of each hormone. The combination of glicentin and PYY increased the predictive power to 0.44, and this increased to 0.51 when ghrelin was added to the model. When adding all 4 hormones secreted from the L-cell (glicentin, oxyntomodulin, GLP-1, and PYY) changes in AUC at 6 months explained 53% of the variance in weight loss. When also adding ghrelin to this linear regression analysis, changes in AUC at 6 months for all 5 hormones explained 60% of the variance in weight loss after bariatric surgery (26). Similar results were found when including only RYGB patients in the analysis (26).
Changes in gastrointestinal hormones and associations with energy intake and energy density
In a pooled analysis of data from both RYGB and SG subjects together, increases in AUC for glicentin (P = .02, R2 = 0.15) and AUC for oxyntomodulin (P = .04, R2 = 0.12) at 6 months were associated with a larger decrease in energy density of food consumed at an ad libitum buffet meal. No associations were found for GLP-1, PYY, and ghrelin, and changes in all gastrointestinal hormones were not significantly associated with reductions in energy intake from the buffet meal (all P ≥ .09) (Table 3).
Associations between change in AUC of glicentin, oxyntomodulin, GLP-1, PYY, and ghrelin from before weight loss to 6 months after surgery and change in energy intake and energy density, respectively, of a buffet meal from before weight loss to 6 months after surgery.
| RYGB and SG (n = 42) | RYGB (n = 32) | |||||
|---|---|---|---|---|---|---|
| β ± SEM | R2 | P | β ± SEM | R2 | P | |
| ΔEnergy intake (kJ) | ||||||
| Absolute change in AUC | ||||||
| Glicentin | –0.02 ± 0.02 | 0.03 | .31 | –0.03 ± 0.03 | 0.05 | .26 |
| Oxyntomodulin | –0.08 ± 0.07 | 0.03 | .31 | –0.11 ± 0.09 | 0.05 | .24 |
| GLP-1 | 0.06 ± 0.24 | <0.01 | .79 | 0.23 ± 0.30 | 0.02 | .45 |
| PYY | 0.11 ± 0.16 | 0.01 | .49 | 0.14 ± 0.19 | 0.02 | .47 |
| Ghrelin | –0.01 ± 0.01 | 0.08 | .09 | –0.01 ± 0.01 | 0.04 | .31 |
| ΔEnergy density (kJ/kg) | ||||||
| Absolute change in AUC | ||||||
| Glicentin | –0.06 ± 0.02 | 0.15 | .02 | –0.07 ± 0.03 | 0.17 | .03 |
| Oxyntomodulin | –0.16 ± 0.07 | 0.12 | .04 | –0.19 ± 0.10 | 0.13 | .06 |
| GLP-1 | –0.30 ± 0.26 | 0.04 | .25 | –0.31 ± 0.36 | 0.03 | .40 |
| PYY | –0.13 ± 0.16 | 0.02 | .44 | –0.15 ± 0.22 | 0.02 | .49 |
| Ghrelin | –0.002 ± 0.01 | <0.01 | .77 | 0.003 ± 0.01 | <0.01 | .76 |
| RYGB and SG (n = 42) | RYGB (n = 32) | |||||
|---|---|---|---|---|---|---|
| β ± SEM | R2 | P | β ± SEM | R2 | P | |
| ΔEnergy intake (kJ) | ||||||
| Absolute change in AUC | ||||||
| Glicentin | –0.02 ± 0.02 | 0.03 | .31 | –0.03 ± 0.03 | 0.05 | .26 |
| Oxyntomodulin | –0.08 ± 0.07 | 0.03 | .31 | –0.11 ± 0.09 | 0.05 | .24 |
| GLP-1 | 0.06 ± 0.24 | <0.01 | .79 | 0.23 ± 0.30 | 0.02 | .45 |
| PYY | 0.11 ± 0.16 | 0.01 | .49 | 0.14 ± 0.19 | 0.02 | .47 |
| Ghrelin | –0.01 ± 0.01 | 0.08 | .09 | –0.01 ± 0.01 | 0.04 | .31 |
| ΔEnergy density (kJ/kg) | ||||||
| Absolute change in AUC | ||||||
| Glicentin | –0.06 ± 0.02 | 0.15 | .02 | –0.07 ± 0.03 | 0.17 | .03 |
| Oxyntomodulin | –0.16 ± 0.07 | 0.12 | .04 | –0.19 ± 0.10 | 0.13 | .06 |
| GLP-1 | –0.30 ± 0.26 | 0.04 | .25 | –0.31 ± 0.36 | 0.03 | .40 |
| PYY | –0.13 ± 0.16 | 0.02 | .44 | –0.15 ± 0.22 | 0.02 | .49 |
| Ghrelin | –0.002 ± 0.01 | <0.01 | .77 | 0.003 ± 0.01 | <0.01 | .76 |
Associations were evaluated using simple linear regression models.
Values in bold represent that the P value is significant (P < 0.05).
Associations between change in AUC of glicentin, oxyntomodulin, GLP-1, PYY, and ghrelin from before weight loss to 6 months after surgery and change in energy intake and energy density, respectively, of a buffet meal from before weight loss to 6 months after surgery.
| RYGB and SG (n = 42) | RYGB (n = 32) | |||||
|---|---|---|---|---|---|---|
| β ± SEM | R2 | P | β ± SEM | R2 | P | |
| ΔEnergy intake (kJ) | ||||||
| Absolute change in AUC | ||||||
| Glicentin | –0.02 ± 0.02 | 0.03 | .31 | –0.03 ± 0.03 | 0.05 | .26 |
| Oxyntomodulin | –0.08 ± 0.07 | 0.03 | .31 | –0.11 ± 0.09 | 0.05 | .24 |
| GLP-1 | 0.06 ± 0.24 | <0.01 | .79 | 0.23 ± 0.30 | 0.02 | .45 |
| PYY | 0.11 ± 0.16 | 0.01 | .49 | 0.14 ± 0.19 | 0.02 | .47 |
| Ghrelin | –0.01 ± 0.01 | 0.08 | .09 | –0.01 ± 0.01 | 0.04 | .31 |
| ΔEnergy density (kJ/kg) | ||||||
| Absolute change in AUC | ||||||
| Glicentin | –0.06 ± 0.02 | 0.15 | .02 | –0.07 ± 0.03 | 0.17 | .03 |
| Oxyntomodulin | –0.16 ± 0.07 | 0.12 | .04 | –0.19 ± 0.10 | 0.13 | .06 |
| GLP-1 | –0.30 ± 0.26 | 0.04 | .25 | –0.31 ± 0.36 | 0.03 | .40 |
| PYY | –0.13 ± 0.16 | 0.02 | .44 | –0.15 ± 0.22 | 0.02 | .49 |
| Ghrelin | –0.002 ± 0.01 | <0.01 | .77 | 0.003 ± 0.01 | <0.01 | .76 |
| RYGB and SG (n = 42) | RYGB (n = 32) | |||||
|---|---|---|---|---|---|---|
| β ± SEM | R2 | P | β ± SEM | R2 | P | |
| ΔEnergy intake (kJ) | ||||||
| Absolute change in AUC | ||||||
| Glicentin | –0.02 ± 0.02 | 0.03 | .31 | –0.03 ± 0.03 | 0.05 | .26 |
| Oxyntomodulin | –0.08 ± 0.07 | 0.03 | .31 | –0.11 ± 0.09 | 0.05 | .24 |
| GLP-1 | 0.06 ± 0.24 | <0.01 | .79 | 0.23 ± 0.30 | 0.02 | .45 |
| PYY | 0.11 ± 0.16 | 0.01 | .49 | 0.14 ± 0.19 | 0.02 | .47 |
| Ghrelin | –0.01 ± 0.01 | 0.08 | .09 | –0.01 ± 0.01 | 0.04 | .31 |
| ΔEnergy density (kJ/kg) | ||||||
| Absolute change in AUC | ||||||
| Glicentin | –0.06 ± 0.02 | 0.15 | .02 | –0.07 ± 0.03 | 0.17 | .03 |
| Oxyntomodulin | –0.16 ± 0.07 | 0.12 | .04 | –0.19 ± 0.10 | 0.13 | .06 |
| GLP-1 | –0.30 ± 0.26 | 0.04 | .25 | –0.31 ± 0.36 | 0.03 | .40 |
| PYY | –0.13 ± 0.16 | 0.02 | .44 | –0.15 ± 0.22 | 0.02 | .49 |
| Ghrelin | –0.002 ± 0.01 | <0.01 | .77 | 0.003 ± 0.01 | <0.01 | .76 |
Associations were evaluated using simple linear regression models.
Values in bold represent that the P value is significant (P < 0.05).
When analyzing only data from RYGB subjects, similar results were found. The change in AUC for glicentin remained negatively associated with changes in energy density (P = .03, R2 = 0.17), and a tendency was found also for oxyntomodulin (P = .06, R2=0.13) (Table 3).
Including glicentin and PYY, oxyntomodulin and PYY, GLP-1 and PYY, GLP-1 and ghrelin, and PYY and ghrelin in the linear regression analysis with energy intake increased the predictive power compared with the sum of the single effect of each hormone. The combination of glicentin, PYY, and ghrelin increased the predictive power to 0.21. Similar results were found when including only RYGB patients (26). The predictive power did not increase when combining multiple hormones in the linear regression analysis with energy density (26).
A mediation analysis showed that the direct effect of glicentin on weight loss accounted for almost two-thirds (62%) of the total effect on weight loss, whereas the remaining effect (38%) was mediated through an effect of glicentin on a decrease in energy density of food consumed. The same pattern was seen for the effect of oxyntomodulin on weight loss, where the direct effect accounted for 64% of the total effect and 36% was mediated through an effect of oxyntomodulin on energy density of food consumed.
Discussion
Postprandial responses of gastrointestinal hormones differed markedly between RYGB- and SG-operated subjects, suggesting that the beneficial effects of these 2 procedures may be caused by different gut hormonal profiles. Increases in postprandial concentrations of glicentin and oxyntomodulin (absolute change in AUC) 6 months after RYGB and SG were associated with better weight losses and with a decrease in preference for energy-dense foods. Combining gastrointestinal hormones increased the predictive power compared with the summed effect of the individual hormones indicating synergistic effects.
Whereas no significant changes were observed following the preoperative diet-induced weight loss, postprandial concentrations of glicentin, oxyntomodulin, and GLP-1 were particularly enhanced following RYGB. In contrast, SG induced a marked decrease in ghrelin in the basal state and throughout the postprandial period. Such differences in postprandial responses of gastrointestinal hormones between RYGB- and SG-operated subjects are in agreement with most previous studies (27–32), but in contrast to others reporting comparably enhanced secretion of especially GLP-1 (33, 34). The exaggerated concentrations of L-cell hormones after RYGB and the lower level of ghrelin after SG are likely due to anatomic differences between the 2 procedures, leading to distinct intestinal nutrient entry rates and passages of nutrients through the gut, and thereby differential exposure of nutrients to enteroendocrine cells (27). However, due to the low number of SG participants, we cannot preclude that the lack of significant postprandial hormone changes after SG may be due to the small sample size rather than a true difference in postprandial responses of gastrointestinal hormones between RYGB and SG.
The enhanced postprandial concentrations of glicentin and oxyntomodulin predicted weight loss 18 months after surgery and were associated with a lower intake of energy-dense foods. Both glicentin and oxyntomodulin are secreted from enteroendocrine L-cells and derive from proglucagon (35). Glicentin contains the entire sequence of oxyntomodulin (which again contains the entire sequence of glucagon) (35) and the rates of secretion of the 2 hormones are highly correlated (26) (22). Oxyntomodulin is a dual agonist for both the GLP-1 and glucagon receptors, and infusions of oxyntomodulin cause weight loss in humans and rodents by reducing food intake and perhaps by increasing energy expenditure (36–38). In contrast, there is no known receptor for glicentin, and the physiological and pharmacological potential of glicentin is unknown (39).
Glicentin and oxyntomodulin are cosecreted together with GLP-1 (22, 40). GLP-1 has a very short half-life of only 1 to 2 minutes (35, 41), whereas oxyntomodulin has a circulating half-life of 12 minutes (42), and the predicted half-life of glicentin is around 30 to 35 minutes (43). Unexpectedly, we found no association between GLP-1 and weight loss, whereas glicentin was found to be the best predictor of the decrease in intake of energy-dense foods and weight loss. However, this does not necessarily indicate a physiological function of glicentin. Instead, we hypothesize that glicentin is the most stable of the proglucagon peptides and thereby may serve as the best marker of the secretion of L-cell hormones, including GLP-1. This would be consistent with the different postprandial levels of the 3 hormones, with glicentin reaching the highest levels, GLP-1 the lowest levels and oxyntomodulin reaching intermediate levels. It should be considered that the total L-cell secretion would be reflected by the sum of the glicentin and the oxyntomodulin concentrations (since oxyntomodulin represents a cleavage product of glicentin) (35). The role of the postoperative exaggerated GLP-1 responses on appetite and food intake has been convincingly demonstrated (10–13,44), whereas less is known about the potential of L-cell hormones to specifically diminish appetite for palatable energy-dense foods. Liraglutide treatment over 16 weeks reduces the desire to eat sweet, salty, savory, and fatty foods when compared with placebo (45). Furthermore, infusion of GLP-1 and PYY reduces reward-related brain responses to palatable energy-dense food cues (44), and studies using Exendin 9–39 (a blocker of the GLP-1 receptor) and Octreotide (a somatostatin receptor agonist) to suppress the effect of these hormones after RYGB show increased reward-related brain responses to such foods (46, 47). These findings support a link between gut hormones and appetite for palatable energy-dense foods.
Our findings are in agreement with data from a recent study, where enhanced postprandial concentrations of glicentin and oxyntomodulin measured 3 and 6 months after RYGB and SG were the strongest predictors of weight loss. Furthermore, enhanced responses of glicentin and oxyntomodulin correlated with increases in subjectively assessed satiety (18). Surprisingly, we found no association between the enhanced responses of anorectic hormones after surgery and changes in energy intake at the buffet meal test. If we investigated these associations using subjective appetite ratings (ie, visual analog scales for hunger and fullness), opposite of what we expected, increases in postprandial responses of glicentin and oxyntomodulin were associated with a decrease in fullness and an increase in hunger (26). Using the same cohort, we have previously reported that energy intake at the buffet meal decreased by 54% (4491 ± 208 kJ vs 2083 ± 208) 6 months after RYGB and SG (9). Given the well-known anorexigenic effect of particular GLP-1 and PYY, we hypothesized that the enhanced responses of these hormones would be associated with the suppression in energy intake.
Currently, the only available gut hormone-based treatment approved for overweight and obesity is GLP-1 agonists. GLP-1 agonists induce average weight losses of 6% to 8%, although 14% of patients can achieve weight loss >15% (48–50). These levels of weight loss are clinically relevant but are insufficient for patients with higher grades of obesity (51), and still modest compared with weight loss obtained with bariatric surgery (52,53). The efficacy of dual and triple gut hormone agonists on food intake and weight loss is currently being established to provide the foundation for developing next-generation therapies, with better outcomes for patients with obesity. Studies investigating the effect of administration of two or more of the gut hormones report synergistic effects of e.g. GLP-1 and PYY (11,12,20,44), and PYY and oxyntomodulin (19) on food intake. Using a statistical approach, we compared the combined effect of different gut hormones on weight loss and consumption behavior with the summed effects of the single hormones on these endpoints. Our results support a synergistic effect of combining multiple gut hormones and suggest several combination strategies that need to be tested in mechanistic studies. When analyzing the combined effect of all 5 hormones we were able to explain 60% of the variation in weight loss 18 months after surgery, indicating that combining early measures of multiple gut hormones can increase the ability to better predict later weight loss. This could potentially be used as an early tool to identify the patients with need for additional postoperative care.
Assessing food intake and food preferences by targeting direct behavior is a major strength of this study. However, our study has the following limitations. First, we report results based on associations rather than causal relationships. Thus, our findings are hypothesis-generating and need to be confirmed in mechanistic studies. Second, the small SG cohort limits the ability to detect changes in hormone responses in this group and to conclude on potential associations between hormone responses and weight loss, energy intake and energy density in SG patients. Third, the fact that we combine both surgery groups in our association analyses could have biased our results. The lower gut hormone response and the lower weight loss in our SG group than in our RYGB group could potentially drive the association between changes in gut hormone responses and later weight loss. However, from the regression plots stratified by type of surgery, it seems that the SG subjects were not a separate group driving the association (26). We, furthermore, found similar results when only RYGB subjects were included in the analysis, although the results did not reach statistical significance, probably due to low statistical power. Studies comparing the effectiveness of RYGB and SG in terms of weight loss show comparable weight loss or a slightly lower weight loss following SG (53–57). In our cohort, SG subjects obtained a substantially lower weight loss than RYGB subjects (difference of 16.2 kg). If we assume, that the smaller weight loss in our SG group is associated with a lower gut hormone response, it would be justified to include the 2 groups in our association analyses. However, if other mechanisms are causing this difference in weight loss, then we may have overestimated the link between changes in hormone responses and postoperative weight loss. Lastly, the inclusion of patients with diabetes could further have affected our results. Patients with diabetes obtained smaller weight losses and smaller increases in glicentin and oxyntomodulin responses after surgery. From the regression plots stratified by diabetes status, again, it seems that the patients with diabetes were not a separate group driving the association (26).
Conclusion
RYGB and SG surgery lead to different gut hormonal profiles, characterized mainly by markedly enhanced secretion of L-cell–derived hormones following RYGB, and markedly reduced ghrelin secretion after SG. Increases in glicentin and oxyntomodulin secretion were found to independently predict successful weight loss 18 months after surgery and were associated with favorable changes in eating behavior. Furthermore, combining multiple gut hormones increased the predictive power compared to the summed effect of single hormones, suggesting synergistic effects. Thus when combining all 5 hormones, we were able to explain 60% of the variation in weight loss 18 months after surgery. Our results should not be interpreted to suggest a regulatory role for glicentin on food choice and weight loss but may reflect that glicentin, because of its longer half-life, is the best marker for the secretion of proglucagon-derived hormones, particularly GLP-1, with already established effects on food intake and weight loss. Our results may imply that early postprandial responses of gut-derived signaling molecules, including glicentin, could be used in the clinic as early markers of inadequate postoperative weight losses in order to identify patients in need of additional postoperative supportive care.
Abbreviations
- AUC
area under the curve
- BMI
body mass index
- GLP
glucagon-like peptide
- PYY
peptide YY
- RYGB
Roux-en-Y gastric bypass
- SEM
standard error of the mean
- SG
sleeve gastrectomy
Acknowledgments
We wish to thank the staff at Bariatric Clinic, Køge Hospital, Denmark, the kitchen and laboratory staff and master’s students at Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark, for helping with recruitment and data collection. Furthermore, we wish to thank Lene Stevner at Department of Nutrition, Exercise and Sports, University of Copenhagen for support with the protocol. A special thanks to all the participants in the GO Bypass study.
Financial Support: This study was carried out as part of the research program “Governing Obesity” funded by the University of Copenhagen Excellence Program for Interdisciplinary Research (www.go.ku.dk). Additional funding was obtained from the Danish Diabetes Academy supported by the Novo Nordisk Foundation, the Lundbeck Foundation and the Aase and Ejnar Danielsens Foundation. N.W.A. and J.J.H. were supported by ERC, grant no. 695069.
Clinical Trial Information: ClinicalTrials.gov: NCT02070081 (registered February 18, 2014).
Additional Information
Disclosure Summary: C.W.l.R. is supported by grants from Science Foundation Ireland (ref. 12/YI/B2480), Health Research Board (USIRL-2016-2), and the Irish Research Council during the conduct of the study. Furthermore, C.W.l.R. reported being on the advisory boards for Novo Nordisk and GI Dynamics, receiving a research grant from AnaBio, receiving honoraria for lectures and advisory work from Eli Lily, Johnson and Johnson, Sanofi Aventis, Astra Zeneca, Janssen, Bristol-Myers Squibb, and Boehringer-Ingelheim, and reported shares in Keyron. The other authors have declared that no conflict of interest exists.
Data Availability: The datasets generated during and/or analyzed during the current study are not publicly available but are available from the corresponding author on reasonable request.
References
