Effect of Gastric Bypass on Spontaneous Growth Hormone and Ghrelin Release Profiles


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Rua Alves Guimarães, 462/72, CEP 05410-000, São Paulo, Brazil. E-mail: mmancini@usp.br


Objective: The purpose of this study was to analyze growth hormone (GH) concentrations in obese women before and after Roux-en-Y gastric bypass (RYGBP) and how resulting changes in weight, fat mass, ghrelin levels, and insulin sensitivity affect GH secretion.

Research Methods and Procedures: Blood was sampled at 20-minute intervals for 24 hours in 10 non-diabetic premenopausal severely obese women before and 6 months after RYGBP. GH concentrations were measured in all samples, and serum ghrelin was collected at five time-points.

Results: After a 27% BMI drop (55.9 ± 6.2 to 40.7 ± 5.8 kg/m2), blunted GH profiles underwent partial recovery. Basal, postprandial, and mean ghrelin concentrations were not changed. A negative correlation was found between mean GH levels and insulin and homeostasis model assessment (p < 0.01). BMI accounted for 54% of GH variation.

Discussion: Partial recovery of GH secretion after RYGBP-induced weight loss suggests that a blunted secretion is not a causal factor of obesity but a consequence of the obese state and does not seem to be ghrelin-level dependent.


The growth hormone (GH)1 axis is altered in human obesity. Spontaneous GH secretion is blunted, as is the GH response to provocative stimuli (1, 2) and binding of insulin-like growth factor 1 to its receptor (3).

Ghrelin is the natural ligand for the GH secretagogue growth hormone receptor 1a (4) and increases appetite, inducing weight gain after administration in rats (5) and humans (6). The periprandial rise in ghrelin levels and postprandial fall suggests a role in meal initiation in humans (7). Paradoxically, ghrelin levels are decreased in obese and increased in lean human subjects (8).

Cummings et al. (9) reported increased ghrelin levels after dietary weight loss but a 72% drop without meal-related oscillations after surgical weight loss. They have hypothesized that Roux-en-Y gastric bypass (RYGBP) suppresses ghrelin secretion through override inhibition, in which episodically stimulated hormones are paradoxically inhibited when that stimulus becomes continuous (permanently empty stomach). Other groups examined the effect of RYGBP on ghrelin, with controversial results (10, 11, 12, 13, 14, 15, 16, 17, 18).

No study has compared GH profiles in severe obesity before and after bariatric surgery. Data related to ghrelin pathway are conflicting. Our hypothesis was that GH secretion is blunted in severely obese women and that it can be restored after RYGBP-induced weight loss. The purpose of our study was to evaluate this hypothesis and to investigate how ghrelin, weight, and insulin resistance affect the putative recovery of GH secretion.

Research Methods and Procedures


Study protocol and informed consent were approved by the Ethics Committee. The investigation was conducted in compliance with the Declaration of Helsinki. Ten non-diabetic severely obese women, 24 to 45 years old, were studied. All normally menstruating, they were tested between the 4th and 10th days of the menstrual cycle, having undergone therapeutic RYGBP by the same surgeon (A.B.G.).

Study Design

The study was a longitudinal prospective analysis. All patients were studied after 3 days of neutral energy balance. On the fourth day, after overnight fasting, the subjects underwent blood sampling at 20-minute intervals for 24 hours, beginning at 8 am, at least 1 hour after forearm venipuncture. Subjects were allowed to ambulate and were given 4 meals/d (8 am, 12 pm, 7 pm, and 10 pm) with fixed calorie level (20%, 30%, 40%, and 10%, respectively, of the total caloric value calculated as 30 kcal/kg per day). Blood was centrifugated <1 hour after sampling, and serum was frozen at −20 °C. This procedure was performed before and 6 months after RYGBP.

Biochemical Assays

Fasting insulin and glucose were measured, and insulin resistance was estimated by homeostasis model assessment (HOMA-IR), calculated as glucose (millimolar) × insulin (milliunits per liter)/22.5 (19).

Serum GH was measured in duplicate by immunoradiometric assay (GH immunoradiometric assay; Immunotech, Marseille, France). The intra-assay and inter-assay coefficients of variation (CV) were <5%, and the detection limit was 0.02 ng/mL. Serum ghrelin was measured by radioimmunoassay (Total Ghrelin; Linco Research, Inc., St. Charles, MO) in five samples (8 am, 10 am, 12 pm, 7 pm, and 2 am) in the same assay (intra-assay CV, 1.35%).

Body Composition Study

All patients were evaluated before and after RYGBP by DXA with a Hologic 4500A densitometer (Hologic Inc., Bedford, MA), based on the measurement of the attenuation of a collimated X-ray beam passing through the body, to estimate fat mass (FM) (20). CV was 4% for FM and 1.9% for lean body mass.

Analysis of GH Profiles

Twenty-four-hour GH profiles were analyzed using the Pulsar program (21), and the following values were extracted: 24-hour mean, baseline value, number of peaks, mean peak amplitude, and peak area. Area under the curve was estimated above calculated baseline.


Pre- and post-surgery groups were compared using Student's paired t test and Wilcoxon rank-sum test. Correlations were tested using Pearson's and Spearman's correlation coefficient. Step-wise multiple regression analysis was used to identify best predictors of GH secretion. Statistical significance level was set at p < 0.05.


After surgery, all patients had experienced a significant reduction in body weight (mean BMI, 40.7 ± 5.8 vs. 55.9 ± 6.2 kg/m2, p < 0.001) and FM (mean 51.9 ± 12.0 vs. 83.1 ± 14.0 kg, p < 0.001).

GH profiles in both cohorts are compared in Table 1. All GH values showed significant differences between subjects before and after surgery. Mean GH concentrations, initially blunted, increased significantly after RYGBP (Figure 1).

Table 1. . Twenty-four-hour mean and basal GH levels, number of peaks, mean peak amplitude, peak area above calculated baseline, and AUCb before and 6 months after RYGBP
 Pre-RYGBP (n = 10)Post-RYGBP (n = 10)p
  1. Values are the mean ± SD (Student's paired t test). GH, growth hormone; AUCb, area under the curve above the calculated baseline; RYGBP, Roux-en-Y gastric bypass.

Basal level (ng/mL)0.04 ± 0.020.08 ± 0.030.019
Mean level (ng/mL)0.20 ± 0.130.79 ± 0.490.003
Peak frequency (n/24 hours)5.5 ± 2.210.8 ± 1.8<0.001
Peak amplitude (ng/mL)0.89 ± 0.572.76 ± 1.120.001
Peak area (ng/mL per minute)0.54 ± 0.401.81 ± 0.780.001
AUCb (ng/mL per minute)3.74 ± 3.1120.8 ± 9.640.001
Figure 1.

Temporal patterns of 24-hour pulsatile GH release before (bottom line) and 6 months after (top line) RYGBP.

Ghrelin values are shown in Table 2. No difference was observed in serum ghrelin before and after surgery.

Table 2. . Serum ghrelin (pg/mL) changes before and 6 months after RYGBP
 8 am10 amChange (%)Mean
  1. Values are the mean ± SD (Student's paired t test). Reference values of plasma ghrelin (non-obese subjects), 403 to 492 pg/mL. RYGBP, Roux-en-Y gastric bypass.

Pre-RYGBP (n = 10)742 ± 174647 ± 260−13694 ± 130
Post-RYGBP (n = 10)765 ± 258810 ± 302+6699 ± 97
p0.820.22 0.91

Linear regression analysis performed in each group separately (pre- and post-RYGBP) between mean GH and BMI, FM, insulin, glucose, HOMA-IR, and ghrelin levels did not show a significant correlation. Considering all patients, we found a significant negative correlation between mean GH and BMI, FM, fasting insulin, and HOMA-IR (Figure 2).

Figure 2.

Correlation between mean GH and BMI (A), absolute FM (B), log insulin levels (C), and log HOMA-IR score (D) in pre- (▪) and post- (□) RYGBP groups. r and p refer to all patients (n = 20).

In a multiple step-wise forward regression analysis with mean GH levels as the dependent variable, BMI was the most inverse determinant of GH secretion, accounting for 54% of GH secretion (r2 = −0.54).


A few studies have been published assessing spontaneous 24-hour GH secretion before and after weight loss in obese subjects, at normal food consumption, when on a diet, or fasting, showing that recovery of GH secretion is inversely related to BMI and visceral FM (22, 23, 24). Our study shows that GH secretory profiles of severely obese women, blunted before RYGBP, are partially restored afterwards.

The pathogenesis of GH insufficiency in obesity is not completely understood. Putative mechanisms include functional compensatory somatotrope responses to the complex altered afferent pituitary signals, such as high fatty acids or hyperinsulinemia.

We did not measure fatty acid concentrations, but insulin sensitivity could be a factor influencing GH secretion pattern (23, 25). We found a significant negative correlation between GH secretion and fasting insulin levels and HOMA-IR. Our results show that BMI was the major negative determinant of spontaneous GH secretion in premenopausal obese women, in agreement with other studies (26, 27).

Cummings et al. (9) published a report suggesting that a decrease in ghrelin secretion might account for the loss of hunger after RYGBP, confirmed by five studies (10, 11, 12, 13, 14). However, three prospective studies found no change (15, 16, 17), and the largest prospective cohort found increased ghrelin levels after RYGBP (18). Cummings’ group found that nutrients infused into the jejunum of rats suppressed ghrelin similarly to infusion into either stomach or duodenum (28); therefore, it is unlikely that the exclusion of these two areas after RYGBP would disrupt ghrelin regulation. No significant difference was found in ghrelin levels before and after surgery. The smaller number of ghrelin samples in our study may have been responsible for the missing relationship between ghrelin and GH. However, a recent report failed to find any relation between frequently measured GH and total and acylated ghrelin in healthy subjects during feeding and after fasting (29).

Ghrelin levels increase before and decrease after meals, but prandial suppression is not universally observed (30). We did not observe significant ghrelin changes before (−13%) and after (+6%) surgery.

In conclusion, after RYGBP-induced weight loss, in severely obese women, partial recovery of spontaneous 24-hour GH profile, initially blunted, was reported, as well as decrease in weight, BMI, FM, and insulin resistance (or some other factor related to the obese state). However, ghrelin is not involved in GH secretory changes. On the other hand, our results suggest that the blunted GH secretion observed in obesity is not a cause but a consequence of the obese state.


We thank Isac Castro for help in statistics. We also thank José Gilberto Vieira (Fleury Laboratories, Sao Paulo, Brazil) and Marcelo Baptista for help in hormone measurements and Margaret and César Boguszewski for the discussion they have stimulated.


  • 1

    Nonstandard abbreviations: GH, growth hormone; RYGBP, Roux-en-Y gastric bypass; HOMA-IR, homeostasis model assessment of insulin resistance; CV, coefficient of variation; FM, fat mass.