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Energy expenditure

Bypass patients demonstrate greater energy expenditure

Study underlines the importance of understanding the gastrointestinal mechanism(s) activating energy expenditure

Gastric bypass patients had greater meal induced energy expenditure compared to patients who had vertical banded gastroplasty nine years after the original procedure, according to a study published online in the journal Plus One.

The authors claim that the outcomes from the study show that the unknown gastrointestinal mechanism(s) activating energy expenditure in association with gastric bypass could lead to novel therapeutic targets for obesity treatments or more effective and safer surgical operations to be designed.

“Long-term weight loss maintenance may require significant changes in several physiological mechanisms, which will be important to understand if non-surgical approaches are to mimic the effects of bariatric surgery,” state the authors.


The study, which investigated the alterations in postprandial energy expenditure after gastric bypass and vertical banded gastroplasty in humans, included 14 women from a randomised clinical trial between gastric bypass. Seven of the patients had a bypass and seven vertical banded gastroplasty. After nine years, patients were assessed for body composition and calorie intake. Energy expenditure was measured using indirect calorimetry in a respiratory chamber over 24 hours and focused on the periods surrounding meals and sleep. Blood samples were analysed for postprandial gut hormone responses.

Postoperatively both the gastric bypass and vertical banded gastroplasty groups had lowered their BMI from 42.2 to 30.8 and 43.0 to 35.0, respectively (p<0.001). The pre and postoperative weights did not differ significantly (p=0.74 and p=0.29, respectively).

Gastric bypass patients had higher EE postprandially (p=0.018) and over 24 hours (p=0.048) compared to VBG patients. Postprandial peptide YY and glucagon like peptide 1 levels were higher after gastric bypass (both p<0.001).

The investigators also reported significant differences between groups for fasting serum levels of free fatty acids, low density lipoprotein (LDL), iron, HbA1c, free thyroxin (fT4), thyroid stimulating hormone (TSH) or creatinine. Gastric bypass patients had elevated levels of high density lipoprotein (HDL) compared to VBG patients. Plasma samples analysed for GLP-1 and PYY in relation to a standardised meal showed exaggerated responses only in the gastric bypass group.

Baseline energy expenditure one hour before dinner intake was similar in both groups. However, during two hours after starting to ingest the 600kcal meal the gastric bypass group, as was the change from baseline in energy expenditure. Energy expenditure was measured after all meals but a significant difference between groups was only seen after dinner which was the meal with the greatest energy content.

The mean 24 hours energy expenditure per total tissue mass was significantly higher for the gastric bypass group, compared to the vertical banded gastroplasty group (p=0.048). Ad hoc analysis of 24 hours energy expenditure per lean tissue or adipose tissue mass was not significantly different between the groups (p=0.30 and p=0.12 respectively).

“The data indicate that despite similar weight loss to vertical banded gastroplasty the patients after the gastric bypass had increased energy expenditure in the early postprandial phase, thereby overcoming the general decrease in energy expenditure that usually follows intentional body weight loss,” the authors write.


They conclude that the study indicates that patients treated with gastric bypass had higher early postprandial energy expenditure compared to patients having similar weight loss following a vertical banded gastroplasty.

The postprandial effect partly explains why 24 hour energy expenditure is higher in gastric bypass patients and why this operation is superior to vertical banded gastroplasty regarding long-term weight loss maintenance.

However, the add that the yet to be determined gastrointestinal mechanism(s) activating energy expenditure in association with gastric bypass may offer novel therapeutic targets for obesity treatments or allow for better and safer surgical operations to be designed.

The authors of this study were Malin Werling, Torsten Olbers, Lars Fändriks, Marco Bueter, Hans Lönroth, Kaj Stenlöf and Carel W le Roux

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