Gastroenterology

Gastroenterology

Volume 138, Issue 5, May 2010, Pages 1845-1853.e1
Gastroenterology

Basic—Alimentary Tract
Gastric Bypass Increases Energy Expenditure in Rats

https://doi.org/10.1053/j.gastro.2009.11.012Get rights and content

Background & Aims

Mechanisms underlying weight loss maintenance after gastric bypass are poorly understood. Our aim was to examine the effects of gastric bypass on energy expenditure in rats.

Methods

Thirty diet-induced obese male Wistar rats underwent either gastric bypass (n = 14), sham-operation ad libitum fed (n = 8), or sham-operation body weight-matched (n = 8). Energy expenditure was measured in an open circuit calorimetry system.

Results

Twenty-four-hour energy expenditure was increased after gastric bypass (4.50 ± 0.04 kcal/kg/h) compared with sham-operated, ad libitum fed (4.29 ± 0.08 kcal/kg/h) and sham-operated, body weight-matched controls (3.98 ± 0.10 kcal/kg/h, P < .001). Gastric bypass rats showed higher energy expenditure during the light phase than sham-operated control groups (sham-operated, ad libitum fed: 3.63 ± 0.04 kcal/kg/h vs sham-operated, body weight-matched: 3.42 ± 0.05 kcal/kg/h vs bypass: 4.12 ± 0.03 kcal/kg/h, P < .001). Diet-induced thermogenesis was elevated after gastric bypass compared with sham-operated, body weight-matched controls 3 hours after a test meal (0.41% ± 1.9% vs 10.5% ± 2.0%, respectively, P < .05). The small bowel of gastric bypass rats was 72.1% heavier because of hypertrophy compared with sham-operated, ad libitum fed rats (P < .0001).

Conclusions

Gastric bypass in rats prevented the decrease in energy expenditure after weight loss. Diet-induced thermogenesis was higher after gastric bypass compared with body weight-matched controls. Raised energy expenditure may be a mechanism explaining the physiologic basis of weight loss after gastric bypass.

Section snippets

Animals and Housing

Thirty adult diet-induced obese male Wistar rats weighing 480–500 g were used for energy expenditure experiments, and 16 adult male Wistar rats weighing 330–350 g were used for morphometric gut analysis. All animals were individually housed under artificial 12-hour/12-hour light-dark cycle and at a room temperature of 21°C ± 2°C unless otherwise stated. Water and standard chow were available ad libitum. All experiments were performed under a license issued by the Home Office United Kingdom

Body Weight

Figure 2 shows the body weight changes for both groups. For the energy expenditure experiments (Figure 2A), body weight was significantly lower in gastric bypass rats compared with the sham-operated, ad libitum fed group from day 5 after surgery. On postoperative day 70, the difference in weight was almost 200 g (sham-operated, ad libitum fed: 603.2 ± 6.6 g vs bypass: 414.3 ± 13.8 g, P < .0001). After a short period of postsurgical weight loss, sham-operated, ad libitum fed rats fed constantly

Discussion

Our data in the rat gastric bypass model are consistent with previous findings that gastric bypass surgery is effective to reduce body weight and especially to maintain body weight loss.4, 9, 10, 12, 16 We confirmed that body weight loss after gastric bypass was associated with a significant loss of fat mass and to a lesser degree of nonadipose body mass.26, 27 Food intake was reduced in gastric bypass rats, which may be partly explained by hormonally mediated mechanisms.9, 16, 28 Importantly,

Acknowledgments

The authors thank Dr Jacquelien Hillebrand (ETH Zürich) and Manuela Munz for help in measurement of body composition and Winnie Ho for assistance with the histology.

K.A.S. is an Alberta Heritage Foundation for Medical Research Medical Scientist.

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    Conflicts of interest The authors disclose no conflicts.

    Funding Supported by the Deutsche Forschungsgemeinschaft (DFG; to M.B.); by the Swiss National Research Foundation (to T.L., C.L.); by a Department of Health Clinician scientist award (to S.B. and C.le R.); support from the NIHR Biomedical Research Centre funding scheme to Imperial College London; by the Markin Undergraduate Student Research Program (to M.W.); and from Canadian Institutes of Health Research (to K.A.S.).

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