Failure of preoperative resting energy expenditure in predicting weight loss after gastroplasty

Surgical weight loss: impact on energy expenditure

Diet-induced weight loss is often limited in its magnitude and often of short duration, followed by weight regain. On the contrary, bariatric surgery now commonly used in the treatment of severe obesity favors large and sustained weight loss, with resolution or improvement of most obesity-associated comorbidities. The mechanisms of sustained weight loss are not well understood. Whether changes in the various components of energy expenditure favor weight maintenance after bariatric surgery is unclear. While the impact of diet-induced weight loss on energy expenditure has been widely studied and reviewed, the impact of bariatric surgery on total energy expenditure, resting energy expenditure, and diet-induced thermogenesis remains unclear. Here, we review data on energy expenditure after bariatric surgery from animal and human studies. Bariatric surgery results in decreased total energy expenditure, mainly due to reduced resting energy expenditure and explained by a decreased in both fat-free mass and fat mass. Limited data suggest increased diet-induced thermogenesis after gastric bypass, a surgery that results in gut anatomical changes and modified the digestion processes. Physical activity and sustained intakes of dietary protein may be the best strategies available to increase non-resting and then total energy expenditure, as well as to prevent the decline in lean mass and resting energy expenditure.

Accuracy of prediction equations for calculating resting energy expenditure in morbidly obese patients

INTRODUCTION

The accuracy of prediction equations for estimating resting energy expenditure (REE) in morbidly obese patients is unclear. The aim of this study was to compare the REE measured using bedside indirect calorimetry with commonly used prediction equations.

METHODS

A total of 31 morbidly obese patients were studied. Pre-operative REE was measured with indirect calorimetry and compared with estimated REE using the Harris-Benedict and Schofield equations. All patients subsequently underwent a Roux-en-Y gastric bypass and measurements were repeated at six weeks and three months following surgery.

RESULTS

The mean age of the patients was 47 years. The mean pre-operative body mass index was 46 kg/m(2). The mean REE measured using indirect calorimetry was 1,980 kcal/day. The estimated REE using the Harris-Benedict and Schofield formulae was 2,195 and 2,129 kcal/day respectively. The equations overestimated REE by 10% and 7%. Body weight and body mass index reduced significantly following Roux-en-Y gastric bypass. There was no significant change in measured REE over the three-month period. After weight loss the difference between the estimated and measured REE reduced to 1-3%.

CONCLUSIONS

Prediction equations overestimate REE in morbidly obese patients. Their accuracy improved after surgery induced weight loss, confirming their validity for the normal weight population. Indirect calorimetry should be used in morbid obesity.

Resting energy expenditure and fuel metabolism following laparoscopic adjustable gastric banding in severely obese women: relationships with excess weight lost

BACKGROUND

Although adjustable gastric banding is increasingly proposed for massively obese patients, little is known about the modifications of resting metabolic rate and substrate oxidation or about metabolic determinants of weight loss following this type of bariatric surgery.

OBJECTIVES

To evaluate the relationships between excess weight loss, resting metabolic rate (RMR) and substrate oxidation, and to identify metabolic predictive factors of weight loss after adjustable gastric banding.

SUBJECTS

Seventy-three obese nondiabetic women aged 39.1+/-10.4 years (18.4-64.8).

DESIGN

Resting metabolic rate and substrate oxidation (indirect calorimetry), body composition (bio-impedance), lipid profile and insulin sensitivity indexes were assessed before and after (13.3+/-6.0 months, range 6.0-31.1) adjustable gastric banding. Patients were classified according to postsurgery time: group A (6-12 months, n=39); group B (12-18 months, n=21); group C (>18 months, n=13). Metabolic parameters associated with the percentage of excess weight lost (EWL) 1 year after surgery were analyzed in univariate and multivariate regressions.

RESULTS

Mean weight loss was 26.2+/-11.4 kg. Mean fat mass loss was 17.3+/-8.1 kg. All biological parameters associated with excess weight improved after surgery. Excess weight lost at 1 year was 45.9+/-17.1% in group A, 47.4+/-17.1% in group B and 51.4+/-18.5% in group C (P=NS). Resting metabolic rate/fat-free mass (FFM) slightly decreased (28.9+/-3.26 vs 30.3+/-2.8, P<0.00001) and RMR/body weight slightly increased (18.5+/-2.8 vs 17.3+/-1.9, P<0.00001) after surgery. Respiratory quotient (0.81+/-0.06 vs 0.82+/-0.05) and FFM-adjusted lipid oxidation (1.10+/-0.41 vs 1.05+/-0.33 mg/min/kg FFM) were not significantly modified after surgery. In multiple linear regression analysis, difference in RMR/body weight, difference in energy sparing, baseline BMI and postsurgery time, were significantly and independently correlated with EWL (total R2=72.5%).

CONCLUSIONS

Adjustable gastric banding promotes gradual but sustained weight loss and is associated with long-term conservation of lipid oxidation and energy expenditure. The individual variability in energy sparing mechanisms predicts weight loss during the first year after surgery.

Alteration of the counterregulatory responses to insulin-induced hypoglycemia and of cognitive function after massive weight reduction in severely obese subjects

The autonomic nervous system (ANS) and hypothalamic-pituitary-adrenal (HPA) axis are reported as activated in excess in the morbidly obese state and, therefore, changes after weight loss can be anticipated. The aim of this study was to investigate the impact of a massive (approximately 30%) weight reduction on the activation of the HPA axis and the ANS following bariatric surgery. Eight (7 women, 1 man) severely obese (125+/-12 kg; body mass index [BMI], 45+/-4 kg/m2) nondiabetic subjects, underwent a 3-hour hyperinsulinemic (1,034 pmol/kg/h) glucose clamp study at hypoglycemia of arterial B-glucose concentration of 3.4 mmol/L. Cognitive function was evaluated by a visuospatial computerized problem-solving test, the Perceptual Maze Test (PMT). The mean weight loss was 40+/-9 kg approximately 12 months postsurgery when their weight was stabilized (85+/-6 kg; BMI, 31+/-3 kg/m2), and insulin sensitivity improved to an average increase of 376%+/-250% (P<.01) of initial value. Before weight reduction, all patients demonstrated brisk peak responses in glucagon, epinephrine, pancreatic polypeptide (PP), norepinephrine, and cortisol, indicative of preserved or exaggerated activation of ANS and HPA axis. In the reduced-obese state, all these responses were attenuated and most markedly so for glucagon, which was totally abolished. In contrast, the growth hormone (GH) response was increased after weight reduction. The cognitive function was clearly modified by weight reduction both during normoglycemia and hypoglycemia and was changed preferentially to a speed-preferring strategy in the reduced-obese state compared with a more accuracy preferred problem-solving process of PMT test presurgery. These results demonstrate a reduction of the glucose counterregulatory hormonal responses, increased insulin sensitivity, and perturbed cognitive function after massive weight reduction. It may be speculated on if the increased insulin sensitivity and reduced counterregulation to hypoglycemia could predispose to low plasma glucose concentrations.

Long-term changes in energy expenditure and body composition after massive weight loss induced by gastric bypass surgery

BACKGROUND

Little is known about the determinants of individual variability in body weight and fat loss after gastric bypass surgery or about the effects of massive weight loss induced by this surgery on energy requirements.

OBJECTIVES

The objectives were to determine changes in energy expenditure and body composition with weight loss induced by gastric bypass surgery and to identify presurgery predictors of weight loss.

DESIGN

Thirty extremely obese women and men with a mean (+/- SD) age of 39.0 +/- 9.6 y and a body mass index (BMI; in kg/m(2)) of 50.1 +/- 9.3 were tested longitudinally under weight-stable conditions before surgery and after weight loss and stabilization (14 +/- 2 mo). Total energy expenditure (TEE), resting energy expenditure (REE), body composition, and fasting leptin were measured.

RESULTS

Subjects lost 53.2 +/- 22.2 kg body weight and had significant decreases in REE (-2.4 +/- 1.0 MJ/d; P < 0.001) and TEE (-3.6 +/- 2.5 MJ/d; P < 0.001). Changes in REE were predicted by changes in fat-free mass and fat mass. The average physical activity level (TEE/REE) was 1.61 at both baseline and follow-up (P = 0.98). Weight loss was predicted by baseline fat mass and BMI but not by any energy expenditure variable or leptin. Measured REE at follow-up was not significantly different from predicted REE.

CONCLUSIONS

TEE and REE decreased by 25% on average after massive weight loss induced by gastric bypass surgery. REE changes were predicted by loss of body tissue; thus, there was no significant long-term change in energy efficiency that would independently promote weight regain.