Effect of Gastric By‐pass on Dietary Protein Bioavailability and Protein Anabolism in Rats

Abstract

IntroductionBariatric surgery is an efficient treatment of massive obesity but it can trigger nutritional deficiencies, especially regarding vitamins and proteins. Protein wasting may be observed although there are large prevalence variations in the literature. Additionally to a low protein intake, protein malabsorption logically appears as a risk factor of protein wasting. However, there is little data on protein digestion after bariatric surgery. Our study aimed to assess the effect of gastric‐bypass (RYGB) on dietary protein bioavailability and protein status in rats.MethodsRats were fed for 3 months an obesogenic diet. Eighteen rats underwent RYGB surgery (survival: n=9) and 10 Sham (survival: n=10) served as control that were pair‐fed. For 15 d post‐surgery, dietary intake, weight and body composition were measured. After 15 d, rats were given a test meal containing 15N labeled proteins. They were sacrificed 6 h after the meal and dietary proteins were quantified in gastrointestinal segments (stomach, duodenum, jejunum, ileum, caecum and colon) by elemental analyzer coupled to isotope ratio mass spectrometer. Small intestine morphology was studied by histology. The protein Fractional Synthesis Rate (FSR) was measured in the liver, kidney, muscle and skin using a 13C valine flooding dose before sacrifice. Results (means ± SEM) were analyzed using a t test (P<0.05).ResultsCompared to baseline, RYGB decreased dietary intake by 49%. Despite pair‐feeding, weight loss was higher in RYGB than in Sham (14±2 % vs 7±0.8 %, P= 0.002), as well as fat mass loss (33±5 % vs 20±1 %, P=0.03). Lean mass loss was 7±1.5 %. in both groups. Six hours after the meal test, there was more dietary nitrogen in the caecum of Sham than RYGB but no difference was detected in other intestinal segments. Real protein digestibility was lower in Sham than RYGB (93.1±0.6 % vs 95.2±0.7%, P=0.03). Histology revealed a hypertrophy of jejunum mucosa in RYGB. The FSR of kidney protein was strongly decreased (P<0.001) in RYGB (72.2±3.2 %/j) compared to sham (98.4±3.3 %/j). Protein anabolism was similar between groups in other tissues.ConclusionWe showed that dietary protein bioavailability was paradoxically improved in RYGB, an effect that can be attributed to the jejunum mucosa hypertrophy. We also revealed that RYGB markedly lowered protein anabolism in the kidney. It will be interesting to identify which protein are involved in this effect.