Metabolic Impact of Dietary Protein Supplementation in Surgical Weight Loss

The goal of this proposal is to study the effect of dietary protein supplementation (PRO-S) during surgical weight loss, on nitrogen balance, energy expenditure, body composition of weight loss, and satiety. The overall goal is to provide evidence-based data on optimal levels of protein supplementation after surgical weight loss by gastric bypass (GBP), a restrictive and malabsorptive procedure, or by vertical sleeve gastrectomy (VSG), a purely restrictive procedure.

We propose a prospective randomized controlled trial (RCT), in which, patients undergoing either GBP or VSG will be allocated to standard PRO-S recommendation ("standard care" according to the American Society for Metabolic and Bariatric Surgery Guidelines) or high supplementation. We will compare 4 groups of subjects:

• Group 1: GBP Standard PRO-S (0.8g protein/kg ideal body weight (IBW)/day
• Group 2: GBP High PRO-S (1.2g protein/ kg ideal body weight (IBW)/ day)
• Group 3: VSG Standard PRO-S (0.8g protein/kg ideal body weight (IBW)/day
• Group 4: VSG High PRO-S (1.2g protein/ kg ideal body weight (IBW)/ day)

AIM#1: Measure total body nitrogen balance (NB) to assess adequacy of levels of protein intake and protein absorption.

AIM#2: Measure the effect PRO-S on lean body mass (LBM), and resting energy expenditure (REE).

AIM#3: Measure the effect of PRO-S on satiety. Hypothesis 3.1: Patients in the High PRO-S group will experience higher levels of perceived satiety compared with patients in the standard PRO-S group.

AIM #4: Study adherence to protein supplementation. Hypothesis : Adherence will be greater in the Standard PRO-S group.

Background and Significance The obesity epidemic has grown rapidly in the United States, and is associated with increased morbidity and mortality rates. Although preventive measures are needed to solve the obesity epidemic in the long-term, bariatric surgery has become a popular and effective treatment of severe obesity. Obesity and its co-morbidities, including type 2 diabetes (T2DM), have a high health care cost2. The cost is even greater for severe obesity (BMI≥40 kg/m2).

Protein (PRO) malnutrition after bariatric surgery (BS) Bariatric surgery (BS) has emerged as the most effective treatment for severe obesity. Gastric bypass surgery (GBP) results in large weight loss with normalization of metabolic functions, including T2DM remission in ~60-80% of cases. Weight loss is very significant (~40-50kg). The rate of weight loss is rapid during the first year after surgery. Surgical weight loss can be associated with vitamin, mineral, and protein deficiencies. PRO malnutrition, remains the most severe nutritional complication associated with malabsorptive surgical procedures. The prevalence of protein malnutrition after malabsorptive BS procedures varies between 3 to 18% and is associated with the length of the bypassed segment. The US recommended dietary allowance (RDA) for protein is ~50 g/d for healthy normal weight adults. Experts and clinicians recommend ~70 g/d of protein during low-calorie diets or 60 g/day (standard) and 120 g/day (high) in the earlier months after BS. However, there is little evidence-based data to support these recommendations. In spite of the absence of level 1 data on types and amount of protein recommendations, the American Society for Metabolic Surgery and BS's website has 14 links for commercial nutrition supplements14. In this study, we aim to study protein absorption and adequacy of protein intake by nitrogen balance in patients following standard and high PRO-S following BS.

Effects of dietary proteins Dietary PRO-S and amino acids (AA) are important modulators of body weight by affecting various determinants of body weight regulation: satiety, thermogenesis, energy efficiency and body composition. During energy restriction, sustaining protein intake at the level of requirement (0.8g protein/kg ideal body weight (IBW)/ day) appears to be sufficient to induce body weight loss while preserving fat free mass (FFM). Protein intake above requirements (1.2g protein/Kg IBW/ day) results in a greater decrease in fat mass and preservation of FFM, but has no effect on body weight loss.

Nitrogen balance (NB) study The NB method is classically used to determine adequate protein intakes and to measure whole body protein balance in response to nutritional interventions. Prolonged negative nitrogen balance should not be sustained for long periods due its negative impact on overall health.

Risk of decreased lean body mass (LBM) and resting energy expenditure (REE) with surgical weight loss BS results in large weight losses (30-50kg), with both fat mass (FML) and LBM losses. Our previous observational studies aiming to evaluate the relationship between protein intake and loss of LBM following BS have shown that protein intake > 60g/ day is associated with better maintenance of LBM after BS. LBM is the main determinant of REE, explaining 75% of the REE variance with REE being the largest component of 24-h energy expenditure (EE). Reduced EE may trigger weight regain in this population. High PRO-S diets may also benefit this population by increasing EE while preventing LBM loss. Increased EE from dietary protein is attributed to an enhanced thermic effect (23-30%) compared to carbohydrates (5-10%) or lipids (2-3%).

Dietary protein intake and satiety High-protein intake increases satiety despite energy restriction. Proposed mechanisms are as follows: a ketogenic state, relatively elevated plasma amino acid (AA) levels, and anorexigenic hormone concentrations feedback on the central nervous system to prolong the duration before one feels hunger for the next meal (satiety) such as, Peptide YY, Glucagon-Like Peptide -1 and cholecystokinin produced in response to peripheral and central detection of amino acid, and decreased levels of the orexigenic hormone ghrelin.

Protein supplementation and adherence Low protein intake after BS has been reported. PRO-S has always been recommended after BS but its feasibility has not been well addressed in any RCT. We will study adherence to PRO-S. Increasing adherence with dietary recommendation is challenging, but may represent a key strategy to improve the clinical nutritional treatment and outcomes after BS.