Characterization of weight loss and weight regain mechanisms after Roux-en-Y gastric
bypass in rats
Ana Guijarro1, Susumu Suzuki1, Chung Chen2, Henriette Kirchner1, Frank A. Middleton3, Sergiy
Nadtochiy4, Paul S. Brookes4, Akira Niijima5, Akio Inui6and Michael M. Meguid1
1Surgical Metabolism and Nutrition Laboratory, Neuroscience Program, Department of Surgery;
University Hospital, SUNY Upstate Medical University, Syracuse, NY 13210.
2Department of Statistics, Management Information and Decision, Whitman School of
Management, Syracuse University, Syracuse, NY 13244.
3Microarray Core Facility, Neuroscience Program, Physiology Department, SUNY Upstate
Medical University, Syracuse, NY 13210.
4Department of Anesthesiology & Mitochondrial Research Interest Group, University of
Rochester Medical Center, Rochester NY 14642.
5Department of Physiology, Niigata University, Niigata, Japan,
6Department of Behavioral Medicine, Kagoshima University Graduate School of Medical and
Dental Sciences, Sakuragtaoka, Kagoshima, Japan
Correspondence author: Michael M. Meguid, MD, PhD, Department of Surgery, University
Hospital, 750 East Adams Street, Syracuse, NY 13210.
Tel: 315-491 2863
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Articles in PresS. Am J Physiol Regul Integr Comp Physiol (July 11, 2007). doi:10.1152/ajpregu.00171.2007
Copyright © 2007 by the American Physiological Society.
Roux-en-Y gastric bypass (RYGB) is the most effective therapy for morbid obesity, but it
has a ~20% failure rate. To test our hypothesis that outcome depends on differential
modifications of several energy-related systems, we used our established RYGB model in
Sprague-Dawley diet-induced obese (DIO) rats to determine mechanisms contributing to
success (RGYB-S) or failed (RYGB-F) RYGB. DIO rats were randomized to RYGB, sham
operated Obese, and sham operated obese pair fed-linked to RYGB (PF) groups. BW, caloric
intake (CI) and fecal output (FO) were recorded daily for 90 days, food efficiency (FE) was
calculated, and morphologic changes were determined. D-xylose and fat absorption were
studied. Glucose-stimulated vagal efferent nerve firing rates of stomach were recorded. Gut,
adipose and thyroid hormones were measured in plasma. Mitochondrial respiratory complexes
in skeletal muscle, expression of energy-related hypothalamic and fat peptides, receptors and
enzymes were quantified. A 25% failure rate occurred. RYGB-S, RYGB-F and PF rats vs.
Obese showed rapid BW decrease, followed by sustained BW loss in RYGB-S. RYGB-F and PF
gradually increased BW. BW loss in RYGB-S rats is achieved not only by a RYGB-induced
decreased CI and increased FO, but also via SNS activation, driven by increased PYY, CRF
and orexin signaling, decreasing FE and energy storage, demonstrated by reduced fat mass
associated with the up-regulation of mitochondrial UCP-2 in fat. These events override the
compensatory response to the drop in leptin levels aimed at conserving energy.
Key words: Food efficiency; gastric bypass; gut and adipose hormones; mitochondria; obesity
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Bariatric operations are currently the only treatment for morbid obesity (defined as a
body mass index of 39 or greater, or weight that is at least 50% above normal). Of the 180,000-
200,000 bariatric operations performed in 2006, ~80% were Roux-en-Y gastric bypass (RYGB).
RYGB also reverses and ameliorates the major cardiovascular and metabolic risk factors,
including type 2 diabetes mellitus and hyper- and dys-lipidemia (12; 72), reduces the long-term
mortality and morbidity associated with obesity and decreases health care costs (15).
Despite the success of the RYGB operation, 20% of patients “ fail to maintain long term
weight loss” . Non surgically-related failure usually occurs within the first three postoperative
years (12), suggesting a metabolic-endocrine compensatory etiological mechanisms.
Weight loss induced by RYGB occurs bi-phasically. Initially there is rapid weight loss
lasting 1-3 years, followed by prolonged weight stabilization (39). Both occur despite a gradual
increase in caloric intake during the same period (72). Our RYGB model in diet induced obese
Sprague-Dawley rats (52) also shows a post-operative bi-phasic weight change pattern. In this
model, ~10-13 rat days is equivalent to 1 human year (62) thus allowing us to follow rats
postoperatively for a considerably long time compared with human subjects.
Conventional surgical belief is that weight loss following RYGB occurs by a) the small
gastric pouch that limits caloric intake; and b) the Roux-en-Y loop of hindgut which short-circuits
the remaining gastrointestinal tract, decreasing nutrient absorption. However, a large body of
evidence suggests that after RYGB, hormonal components play a major role in reducing food
intake and decreasing weight (6; 17).
Other mechanisms are initiated while creating the gastric pouch because it divides vagal
parasympathetic and sympathetic fibers (60), therefore influencing the afferent signals to the
brain, while efferent signals can also be disrupted, which may play a role in the outcome of this
operation. However, these mechanisms do not sufficiently account for the maintenance of body
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weight loss or regain after RYGB, suggesting that nutrient-hormone changes could define a
successful or failed operative outcome.
Mitochondria play a fundamental role in thermogenesis and energy regulation. Major
modifications in oxidative phosphorylation and mitochondrial metabolism occur in obesity (53).
Proton leak across the mitochondrial inner membrane, which is catalyzed by uncoupling
proteins (26) and that bypasses ATP production, may account for 25% of the standard
metabolic rate in the rat (66). Hepatic mitochondrial proton leak is positively correlated with
standard metabolic rate (10), and is affected by the thyroid status, being 4-fold greater in
hyperthyroid rats (33). Skeletal muscle mitochondria are also relevant in the context of energy
homeostasis. Thus, a decrease in skeletal muscle mitochondrial mass and function is
associated with accelerated rate of fat recovery (catch-up fat) and insulin resistance which are
characteristic features of weight recovery after caloric restriction (16).
We postulate that the outcome after RYGB depends on differential modifications of
several energy-related systems. To test our hypothesis we studied the changes in body weight,
food intake, nutrient absorption, fecal output, food efficiency, body composition and
metabolically-relevant nutrient and hormones in diet-induced obese Sprague-Dawley male rats
and examined the changes in electrical activity of the efferent vagal fibers innervating the gastric
pouch. In addition, we measured numerous transcripts in the hypothalamus and subcutaneous
fat involved in the modulation of food intake, metabolism and energy homeostasis as well as
mitochondrial function in skeletal muscle.
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MATERIALS AND METHODS
The Committee for the Humane Use of Animals at SUNY Upstate Medical University
approved the experiments, and animal care was in accordance with guidelines established by
the National Institute of Health.
The pre-operative protocol to induce obesity in the Sprague-Dawley male pups, our
operative procedures in which the subdiaphragmatic vagal trunks are preserved and the post-
operative management of the rats were previously described (52). To induce obesity, pups were
fed a high energy diet (HED, D12266, Research Diets®, New Brunswick, NJ) for 16 weeks (74).
After inducing obesity, obese rats were stratified according to body weight to ensure similar
average starting body weight before the following surgical procedures: 1.Sham operated obese
controls (Obese), which continued to eat ad libitum; 2. Roux-en-Y gastric bypass rats (RYGB)
and 3. Sham operated obese rats that were pair fed (PF) by being given the same amount of rat
chow to eat, as consumed the previous day by its paired RYGB rat. After surgery, rats were fed
with rat chow (Rat Chow Diet # 5008; Ralston Purina, St Louis, MO).
After the procedure, rats were followed for 90 post-operative days and then euthanized,
in a non-fasting state, starting at 9am. Because eight rats were euthanized in one day and the
harvesting of blood and tissue took approximately 60 minutes, this would result in fasting rats for
different periods that would introduce the variable of ‘ fast-duration’ , which has metabolic
consequences of relevance to our investigation. Therefore to avoid this variable the rats were
not fasted. The groups consisted of Obese, n = 10; RYGB, n = 12, [consisting of RYGB rats that
successfully lost weight: RYGB-S, n = 8; and RYGB rats that failed to sustain weight loss by
regaining weight: RYGB-F, n = 4], and PF, n = 8 (see General Statistical Analysis).
Based on the observed weight loss pattern derived from the above study, only Obese (n
= 10) and RYGB (n = 12) rats had absorption studies done on POD 30, 60 and 90.
Body weight, caloric intake, fecal output, food efficiency and body composition
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Postoperatively, daily body weight, food intake and fecal output were measured
gravimetrically for 90 days. Food intake was computed as caloric intake, because between post-
operative days 1-8 the rats had a liquid diet. They also had liquid stool and thus fecal weight
was measured only after solid food was given. Fecal output is expressed as fecal weight per
one g food intake x 100. Food efficiency, an index of nutrient assimilation into body mass, was
calculated as a ratio of change in body weight to cumulative caloric intake and expressed as
At 90 days the rats were anesthetized using isoflurane, decapitated and muscle
(representing the combined weight of left gastrocnemius plus soleus), fat depots (abdominal
subcutaneous, mesenteric, epididymal and retroperitoneal) and visceral organs (liver, heart and
pancreas) were dissected out and weighed, reflecting morphological changes and body
composition. Fat mass was the sum of the weights of the fat depots, while fat free mass was
calculated by subtracting fat mass from body weight. The above parameters were expressed as
a percent of body weight.
D-xylose and fat absorption
Before testing, rats were food deprived for 16h. D-xylose solution (0.5 g/kg; 20% w/v)
was gavaged via a trans-oral tube into the gastric pouch of RYGB rats or the stomach of Obese
without anesthesia. Urine was collected for 5h to measure the amount of excreted D-Xylose (23).
D-xylose absorption was calculated as (%) = urine D-Xylose (g)/administered D-Xylose (g) x
100. To measure fat absorption stool was collected for 72 h before POD 30, 60 and 90 and its
fat content was extracted and measured (76). Fat absorption (%) per day = Fat intake (g) - Stool
fat (g) (44). A PF group of rats was not included at the time of the study, because their
gastrointestinal tract was not surgically altered and was thus anatomically similar to the Obese.
We made the assumption that the absorption would thus be the same, based on supporting
data from our lab, in a different experiment, showing no differences in the disaccharidase
activity in proximal, distal jejunum and ileum in PF rats compared to Obese.
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Metabolically-relevant nutrients and hormones
After decapitation, mixed arterial and venous blood, in none fasted rats, was collected
into EDTA-rinsed tubes. It was centrifuged at 3,000 rpm for 10 min at 4°C for plasma. Samples
were stored for a limited time at –80°C before analysis in duplicate. Plasma glucose, total
cholesterol, triglycerides, and free fatty acids (FFA) were measured by enzymatic colorimetric
kits (WAKO®, Richmond, VA). Plasma polypeptide YY (PYY) (DSL®, Webster, TX), CCK,
ghrelin (Phoenix®, Belmont, CA), insulin (ALPCO®, Windham, NH), leptin (R&D Systems®,
Minneapolis, MN), free triiodotyronine 3 (T3) (Alpha Diagnostic, TX) were measured using
Efferent vagal nerve firing rates of gastric pouch
In a smaller separate set of rats (Obese, n=3 and RYGB, n=4) repeated measurements
of vagal efferent nerve firing rates of the gastric pouch were calculated before and after a
glucose challenge at 90 days. The methodological details of similar studies were previously
described in detail (54). Rats were food deprived for 6 h and anesthetized using intra-peritoneal
injection of urethane (1g/kg BW). The abdomen was opened and using a dissection microscope
the vagal gastric efferent nerve was isolated and divided. The central cut end was placed on a
silver wire recording electrodes to record efferent discharges. 5 % glucose in 5 ml water was
gavaged into the gastric pouch of RYGB rats or the stomach of Obese. The mean number of
vagal efferent firing impulses per 5 seconds was determined in 10 successive 50 second
periods. This measurement was repeated every 30 minutes for 180 to 210 minutes in response
to the 5% glucose solution. These results were compared between the groups after conversion
of raw data to standard pulses by a window discriminator, which separated study generated
discharges from background noise.
Blue native gels electrophoresis of skeletal muscle mitochondrial protein complexes
To determine the relative amounts of mitochondrial respiratory complexes contained
within skeletal muscle (gastrocnemius and soleus) samples at 90 days, frozen tissue (75 mg)
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was homogenized (glass Dounce homogenizer) in 2 ml of extraction buffer (440 mM sucrose,
20 mM MOPS, 1 mM Di-Na+ EDTA, 0.2 mM PMSF, pH7.2 at +40C), and centrifuged at 500 x g
for 2 min. The pellet was discarded, and 1ml of supernatant was centrifuged at 14,000 x g for 10
min. The pellet from this spin (nominal mitochondrial fraction) was resuspended in 200 µl of
buffer (0.75 mM Aminocaproic acid, 50 mM BisTris, 1% (w/v) dodecyl-β-D-maltoside, pH7 at
40C), and was kept on ice for 10min. with occasional mixing. The mixture was then centrifuged
at 14,000 x g for 10 min, and to the supernatant (100 µl) was added 9 µl of Coomassie Blue
suspension (0.5 M Aminocaproic acid, 5% Coomassie Blue) before loading directly onto gel.
Blue-native gel electrophoresis was performed as previously described with minor modifications
(11). Gels were run at a constant 40 V for 1h with Hi-Blue cathode buffer (50 mM Tricine, 15
mM BisTris, 0.02% Coomassie Blue, pH7 at +40C), and then at 20 V overnight with Lo-Blue
cathode buffer (50 mm Tricine, 15 mM BisTris, 0.002% Coomassie Blue, pH7 at + 40C). Gels
were stained in a solution of Coomassie Blue R-250 and G-250 (0.05 w/v each in 10 % acetic
acid and 25% isopropanol, pH 7 at +40C) for 3 hours, and then destained in 10 % acetic acid
+25% isopropanol. The relative amount of mitochondrial respiratory complexes contain within
skeletal muscle samples was assessed by optical densitometry with Scion Image software
(Scion Corp, Frederick, MD).
Short tandem repeats (STRs)
We genotyped 8 short tandem repeats (STRs) that are highly polymorphic between
Sprague-Dawley and other closely-related strains (Wistar, Wistar-Kyoto, Spontaneously
Hypertensive). The STRs were amplified using hepatic DNA from one RYGB-S and three
RYGB-F rats. The hepatic DNA was purified using the MasterPure kit (Epicentre
Biotechnologies, Madison, WI) and PCR was performed to amplify the STR sequences using
primers based on the Rat Genome Database records for specific STR sequences (and provided
by Drs. R. Hoopes and S. Scheinman at SUNY Upstate, NY). The STRs were chosen to
interrogate three different chromosomes (1-3) at approximately every 60 megabases. The 8
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STRs included were: D1RAT196, D1RAT193, D1MIT32, D2RAT6, D2RAT88, D2RAT171,
D3MGH16, and D3MIT13. The PCR products of these reactions were resolved on a 4%
agarose/ethidium bromide stained gel by electrophoresis (80V, 1 hour) and compared to the
SSLP expected size database for different rat strains available on the Rat Genome Database.
Microarray of whole hypothalamus and peripheral fat
To examine the possibility that changes in expression of specific genes and gene groups
might underlie the failure of certain rats to sustain weight loss following RYGB, we performed
gene expression analysis with oligonucleotide microarrays (RAE230 2.0, Affymetrix) on three
groups of male rats: RYGB-S (n=8), RYGB-F (n=3) and PF controls (PF, n=3). For each animal,
total RNA was isolated from homogenates of an entire hypothalamus from one hemisphere and
a sampling of subcutaneous abdominal fat, using the RNeasy kit (Qiagen). We had a large
number of successful animals (RYGB-S rats) with tissue available. Thus, we chose to use a
partial pooling design for establishing the baseline expression values for the RYGB-S rats which
showed the expected outcomes. For RYGB-F and PF groups, the RNA from three individual
animals was used for microarray analysis. For the RYGB-S group, the eight total RNA samples
for each tissue type were divided into three separate pools (each of which contained RNA from
2 or 3 rats) for microarray analysis using an equal quantity of RNA from each animal. In total, 18
GeneChip hybridizations were performed comparing the three treatment groups (RYGB-S,
RYGB-F, PF) and the two tissue types (hypothalamus and fat) using three independent
replicates for each. Amplification and labeling of RNA was performed using the WT-Ovation™
RNA Amplification System (NuGen), and hybridization, washing, staining and scanning of the
GeneChips performed according to standard protocol (GeneChip Expression Analysis Technical
Manual 701021 rev 5, Affymetrix). After scanning, the microarray images were processed using
GeneChip Operating System (GCOS) software to obtain performance metrics, and prepared for
data analysis using the RMA normalization method (36). After obtaining RMA-based estimates
of gene expression levels, individual transcripts in each of the three experimental groups and
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two tissue types were compared using a two-way analysis of variance (2 x 3 ANOVA)
comparing tissue type (hypothalamus or fat) and treatment group (RYGB-S, RYGB-F, PF).
Because our primary aim was on determining possible causes of the failure to sustain weight
loss in the RYGB-F animals, we focused the present analysis on a subset of 667 probes that
were determined to be involved in feeding, digestion, or general carbohydrate, lipid and protein
metabolism using the online NetAffx tool (Affymetrix). A list of these probes is posted at
http://www.upstate.edu/sunymac/Meguid.xls. A table of the genes showing a significant main
effect of treatment in either tissue type (uncorrected p < 0.05) was generated, and post-hoc
analyses (Fisher’ s Protected LSD) were performed to determine the specific comparisons
showing significant effects.
After the operation, time series plots of the daily body weight, food intake and fecal
output was plotted for each individual rat to show changing patterns. To determine the change
or inflection point (change point day) of each daily characteristic during the rapid and gradual
weight loss periods after operation for 90-days, a switching quadratic trend analysis was
performed, to identify the change point day of mean body weight, caloric intake and fecal output
in Obese, RYGB and PF rats. The exact time point was estimated based on the smallest
average error(s) and the highest adjusted R2for each possible time period between t=0 and
t=90. When the switching quadratic trend analysis was applied to the body weight series of each
individual rat and the mean body weight series of each of the study groups, it revealed two
separated RYGB cohorts: RYGB-weight loss (RYGB-S) and RYGB-weight regain (RYGB-F).
Thus further comparisons and analyses were conduct separately with respect to the four
experimental groups: Obese, RYGB-S, RYGB-F and PF. In the RYGB-S, RYGB-F and PF rats
a switching quadratic trend model was used to optimally analyze the data, while a switching
linear trend model fitted the Obese rat data. A linear trend model for change point analysis as
used for mean daily caloric intake and fecal output fitted the postoperative Obese, RYGB-S,
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RYGB-F and PF rat data more optimally. Comparisons of daily body weight, caloric intake, fecal
output, feeding efficiency and organ weight in the four study groups were analyzed using one-
way ANOVA and Tukey’ s pair-wise multiple-comparison test with the join error rate equal to
0.05. To assess the differences in D-xylose and fat absorption between Obese and RYGB rats
and with time one-way ANOVA and Tukey’ s pair-wise multiple-comparison test with the join
error rate equal to 0.05 was done and data are reported as Mean ± S.E.M. Vagal nerve firing
rates of gastric pouch. Differences in efferent firing rates were evaluated using one-way ANOVA
and t-test. Data are reported as Mean ± S.E.M. Microarray data were analyzed by two-way
ANOVA and post-hoc analyses (Fisher’ s Protected LSD) were performed to determine the
specific comparisons showing significant effects. Densitometric data from blue native gels were
analyzed by two-way ANOVA, with p < 0.05 being considered significant.
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Body weight and caloric intake
These inter-related indices are plotted together in Figure 1A and B. The preoperative
body weight of all RYGB rats (n = 12) was 765.76 ± 8.10 g. The switching quadratic trend
analysis of daily body weight showed that after RYGB operation, 4 of the 12 rats, after an initial
period of body weight loss, began to regain weight i.e.: the RYGB operation failed (RYGB-F,
n=4), so that by postoperative day 90 they weighed more (p < 0.001) than the remaining RYGB
rats that successfully continued to lose weight (RYGB-S, n = 8), as shown in Figure 1A.
The change point day, as well as the quantitative changes in mean body weight and
mean daily change in body weight before and after change point day is shown in Table 1. In the
immediate postoperative period the Obese lost 7.0 ± 0.7 % of their initial body weight until
change point day on day 9 (Table 1). With the switch to solid chow, the Obese gained weight
until the end of the study, when they weighed 4.3 ± 3.5 % more than the initial body weight.
After the operation RYGB-S rats also lost weight rapidly (15.4 ± 0.6 % of their initial body
weight) but, despite the switch to chow, continued to lose weight until change point day at day
22 (Table 1) after which body weight loss stabilized, decreasing by 33.5 ± 2.6%, compared to
their starting body weight, on day 90. Initially, the RYGB-F and the PF rats rapidly lost body
weight until change point day at days 24 and 23 , respectively (at which point RYGB-F rats had
lost 10.8 ±1.4 %, while PF rats had lost 7.7 ± 1.5 %). This was followed by a 10.9 ± 2.3 % regain
in body weight for RYGB-F rats and an 8.8 ± 5.0 % in PF rats. By day 90, the RYGB-S rats had
lost a greater percentage of body weight (p < 0.001) vs.RYGB-F rats (14.2 ± 1.1%) and PF rats
(13.4 ± 3.5%). The body weight pattern of RYGB-F and PF rats was similar with no difference in
the percentage of body weight loss (p = 0.997), which however was lower than their initial body
weight by day 90.
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The preoperative caloric intake was 101.4 ± 6.1 Kcal/day. After operation, when rats
were started on a liquid diet, the Obese ate 46.1 ± 4.7 Kcal/d, while RYGB-S rats ate 16.9 ± 2.0
Kcal/d and RYGB-F rats ate 15.9 ± 1.9 (Figure 1B). On day 9 chow was provided and caloric
intake increased in all groups, as shown in Figure 1B. This occurred during the same time that
body weight was decreasing until their respective change point day. As shown in Table 2, the
change point day was on day 25 in Obese; day 34 in RYGB-S, day 30 in RYGB-F and day 34 in
PF rats. After each change point day, caloric intake remained relatively stable until the end of
The quantitative changes in mean caloric intake and in mean daily change in caloric
intake before and after change point day are shown in Table 2. Although caloric intake
increased between day 9 and change point day in all groups, it remained significantly lower in
RYGB-S and in PF rats vs. Obese (p = 0.005, and p = 0.006, respectively). Caloric intake in
RYGB-F rats vs. Obese was lower, but it was not statistically different (p = 0.105, Table2).
Between change point day and day 90 mean caloric intake in RYGB-S rats was lower vs. the
remaining groups (p < 0.001), while in RYGB-F rats it was higher vs. both RYGB-S and PF rats
(p < 0.001), although it was not different vs. Obese (p = 0.920). Caloric intake in the PF rats vs.
Obese was lower (p < 0.001). Throughout the study there were no differences (p > 0.05, Table
2) in the daily mean change in caloric intake among the groups.
Because immediately after operation rats were on a liquid diet, their liquid stools were
not quantified. After the introduction of solid chow, feces became formed and were quantitated
and as shown in Table 3, from day 9 to change point day, there were no differences in the ratio
of fecal weight per one g food intake among groups.
But from change point day to the end of the study, RYGB-S and RYGB-F rats put out
significantly greater amounts of feces vs. both the Obese and PF cohorts in whom
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gastrointestinal tract was intact (p < 0.001). RYGB-S rats had also a greater fecal output than
RYGB-F rats (p < 0.001). No differences were found between PF group and Obese (p = 0.752).
D-xylose and fat absorption
At day 30, D-xylose absorption (Figure 2A) decreased in RYGB-S rats vs. Obese (p =
0.001), while in RYGB-F rats it was similar to Obese (p = 0.725). D-xylose absorption at day 60
and 90 was not significantly different in both RYGB groups vs. Obese (p > 0.05), while there
was no differences between RYGB-S and RYGB-F rats at any time point (p > 0.05).
In contrast, fat absorption (Figure 2B) was significantly lower in both RYGB-S and
RYGB-F rats vs. Obese at POD 30, 60 and 90 (p < 0.001) but no differences were found
between RYGB-S and RYGB-F rats (p > 0.05) at any time point, nor within each group with time
(p > 0.05).
Between days 0 to 8 the food efficiency was negative in all groups (Figure 3A) and in
RYGB-S rats was significantly lower than in Obese (p < 0.001), RYGB-F (p = 0.046) and PF (p
= 0.019) rats. Both RYGB-F (p = 0.022) and PF (p = 0.002) rats had a lower food efficiency than
Obese rats but there were not significant differences between them (p = 0.999). From day 9 to
change point day (Figure 3B) no differences were found among groups (p > 0.05) although
RYGB-S rats had a lower food efficiency compared to the remaining groups, but which was not
statistically different (p > 0.05). From change point day to day 90 (Figure 3C) food efficiency
improved, becoming positive in Obese, RYGB-F and PF rats, while remaining negative and
significantly lower in the RYGB-S rats compared to Obese (p = 0.002), RYGB-F (p = 0.029) and
PF (p = 0.011) rats.
At day 90, in RYGB-S (p < 0.001), RYGB-F (p < 0.001) and PF (p = 0.007) rats total fat
mass (expressed as a percentage of body weight) was lower than in Obese (Table 4). In RYGB-
S rats, total fat weight was also lower than in PF rats (p < 0.001), while there were no
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differences between RYGB-F rats and PF group (p = 0.543). The percentage of fat mass in
RYGB-S was lower than in RYGB-F rats but the difference was not statistically significant (p =
0.110). The reduction in the percentage of fat mass relative to Obese was 71.5 ± 3.4% in
RYGB-S rats, 47.1 ± 11.1% in RYGB-F rats and 27.4 ± 5.5% in PF group.
The percentage of fat free mass (Table 4) was higher in RYGB-S (p < 0.001), RYGB-F
(p < 0.001) and PF (p = 0.007) compared to Obese.. In RYGB-S rats, the percentage of fat free
mass was higher than in PF rats (p < 0.001), while there was no statistical differences between
RYGB-F and PF (p = 0,263) or RYGB-S and RYGB-F (p = 0.110).
At day 90, liver weight, as a percentage of body weight (Table 4), was lower PF rats
compared to Obese (p = 0.016), RYGB-S (p < 0.001) and RYGB-F (p = 0.002). There was no
difference RYGB-S vs. Obese rats (p = 0,423), RYGB-F rats and Obese (p = 0,277) or RYGB-S
vs. RYGB-F (p = 0,877). The pancreas weight, expressed as a percentage of body weight, did
not change with RYGB or caloric restriction (p > 0.05, Table 4). As shown in Table 4, the
percentage of heart weight was higher in RYGB-S rats compared to both Obese (p < 0.001) and
PF rats (p = 0.023). No differences were found among the remaining groups (p < 0.05). The
percentage of the skeletal muscle weight was not different among groups (p < 0.05; Table 4).
Metabolically-relevant nutrients and hormones
Relative to Obese plasma glucose was decreased in RYGB-S and RYGB-F rats (p <
0.001) and PF group (p = 0.010), as shown in Table 4. Plasma glucose was also decreased in
RYGB-S rats vs. PF group (p = 0.042), but was not different between both RYGB groups (p =
0.999) or between RGYB-F and PF rats (p = 0.204).
Total cholesterol was lower in RYGB-S rats vs. Obese (Table 4, p < 0.001) and it was
lower in RYGB-F rats and PF group vs. Obese, but not statistically different. No differences
were found among the remaining groups (p > 0.05). A decrease in plasma triglycerides occurred
in RYGB-S (p = 0.001), RYGB-F rats (p = 0.018) and PF group (p = 0.005) compared to Obese.
Free fatty acid (FFA) concentrations were similar in all groups (p > 0.05).
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