The effect of high protein diets on weight loss and lean muscle mass in patients awaiting bariatric surgery: A pilot study

Abstract

Background: Obesity is a global epidemic associated with many adverse health outcomes such as type 2 diabetes, cancer and heart disease. New Zealand contributes to the obesity statistics with almost two thirds of the population now classified as overweight or obese. Many treatment options for obesity are now available including diet modification, exercise regimens, pharmacological treatments and bariatric surgery. A component of bariatric surgery programmes is to engage in diet and exercise lifestyle changes. A marker of this is weight loss. It is unknown which diet composition is the most effective for weight loss and muscle mass retention in this population. Aim: A randomised controlled pilot trial to investigate the effects of a high versus a low protein diet for weight loss in 24 obese adults awaiting bariatric surgery. The primary outcomes of this study were excess percentage weight loss, percentage weight loss and total body muscle mass after following a prescribed diet. The secondary outcome of the study was to investigate the adherence to each diet regimen. Methods: Obese (BMI >30kg/m2) individuals awaiting bariatric surgery completed an eight-week low calorie diet. The low calorie diet consisted of 1200kcal/day for females and 1500kcal/day for males. Patients were randomly prescribed either a high protein diet (30% intake protein) or a low protein diet (15% intake protein). Body composition, circumference measurements and 24-hour urine samples were completed at baseline and eight weeks. A food diary was completed at four weeks to assess energy intake, macronutrient composition and adherence. Participants completed a survey after the eight-week point to assess reasons for non-completion or dropout. Results: Of the 24 individuals that were randomised, 14 individuals completed the 8-week measurements. No significant difference in weight loss was seen between the diet groups (p=0.289). Muscle mass retention and body fat loss appeared greater in the high protein group compared to the low protein group however this was not statistically different between groups (p=0.314, p=0.379). The low protein group had significantly greater decreases in the neck and hip circumference than those on the high protein diet (p=0.03, p=0.02 respectively). Food diaries showed trends that adherence was low and energy intake was lower on the high protein diet however did not differ significantly from low protein diet group (p=0.178). The average difference between protein groups was 7.2g. Urine samples showed trends towards greater increases in urea, creatinine, and albumin to creatinine ratio in the low protein groups (p=0.413, p=0.06, p=0.03). Conclusions: The results of this study show there was no greater effect of a high protein diet compared to a low protein diet on short-term weight loss in obese participants. Adherence to the given energy restriction was low. Positive trends were evident, yet due to a small sample size there was little statistical significance in the results. Future research should be conducted with a larger population to investigate whether results would show which diet composition is more effective for weight loss and beneficial for body composition. Keywords: protein, diet, bariatric, obese, low calorie diet, weight loss, muscle mass