Bariatric surgery may induce protein malabsorption, although data are scarce. This study aims at evaluating dietary protein bioavailability after different bariatric surgeries in rats. Diet-induced obese Wistar rats were operated for vertical sleeve gastrectomy (VSG) or Roux-en-Y gastric bypass (RYGB). The control group was composed of pair-fed, sham-operated rats (Sham). Two weeks after surgery, rats were fed a 15N protein meal. Protein bioavailability was assessed by determination of 15N recovery in the gastrointestinal tract and organs 6 h after the meal. Fractional protein synthesis rate (FSR) was assessed using a flooding dose of 13C valine. Weight loss was the highest in RYGB rats and the lowest in Sham rats. Surprisingly, RYGB (95.6 ± 0.7%) improved protein digestibility ( P = 0.045) compared with Sham (93.5 ± 0.5%) and VSG (93.8 ± 0.6%). In contrast, 15N retained in the liver ( P = 0.001) and plasma protein ( P = 0.037) was lower than in Sham, with a similar trend in muscle ( P = 0.052). FSR was little altered by bariatric surgery, except for a decrease in the kidney of RYGB ( P = 0.02). The 15N distribution along the small intestinal tissue suggests that dietary nitrogen was considerably retained in the remodeled mucosa of RYGB compared with Sham. This study revealed that in contrast to VSG, RYGB slightly improved protein digestibility but altered peripheral protein bioavailability. This effect may be ascribed to a higher uptake of dietary amino acids by the remodeled intestine. NEW & NOTEWORTHY Using a sensitive 15N meal test, we found that gastric bypass slightly improved protein digestibility compared with sleeve gastrectomy or control but, in contrast, lowered protein retention in the liver and muscles. This paradox can be due to a higher uptake of dietary nitrogen by the intestinal mucosa that was hypertrophied. This study provides new insight on the digestive and metabolic fate of dietary protein in different models of bariatric surgery in rats.

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Background In the context of developing plant protein sources for humans, sunflower is a good candidate in its form as an oilseed coproduct. Objectives We aimed to compare the real digestibility in rats of a sunflower isolate to that of goat whey protein. We also studied the efficiency of 15N and 2H intrinsic labeling in this assessment. Methods Sunflower seeds and goat milk were labeled with 15N and 2H. Male Wistar rats (10 wk old) were fed a meal containing 12% of either sunflower isolate (n = 8) or whey (n = 8). Six hours after meal ingestion, protein and amino acid digestibility were assessed by measuring nitrogen, hydrogen, and amino acids in the digesta, as well as isotope enrichments in the bulk and individual amino acids. The differences between groups and isotopes were respectively tested with an unpaired and a paired t test. Results Protein isolate purity was 87% for whey and 94% for sunflower. 2H and 15N enrichments were, respectively, 0.12 atom % (AP) and 1.06 AP in sunflower isolate and 0.18 AP and 0.95 AP in whey. Fecal 15N protein digestibility was 97.2 ± 0.2% for whey and 95.1 ± 0.5% for sunflower isolate. The use of 2H resulted in a lower digestibility estimate than 15N for whey (96.9 ± 0.2%, P < 0.05) and sunflower (94.2 ± 0.5%, P < 0.01). For both isotopes, protein digestibility was about 2% higher for whey than for sunflower isolate. Mean 15N amino acid caecal digestibility was 97.5 ± 0.2% for whey and 96.3 ± 0.2% for sunflower isolate. The values obtained with 15N and 2H resulted in significant differences ranging from −0.1% to 3.5%. The DIAAS was >1.0 for whey and 0.84 for sunflower (lysine). Conclusions The protein and amino acid digestibility of sunflower isolate was high but its DIAAS reflected a moderate lysine imbalance. Despite slight differences with 15N, deuterium produced comparable results, making it suitable for in vivo digestion studies.

Background Sunflower is a promising protein source but data on amino acid (AA) digestibility are lacking in humans. Classically, the determination of AA digestibility requires ileal digesta sampling. The dual isotope method is minimally invasive but has not been compared to the conventional approach. Objective This study aimed to determine the true ileal digestibility of sunflower AAs in healthy volunteers who ate biscuits containing 15N protein isolate, in comparison with the dual isotope method. Methods Twelve healthy volunteers (men and women, 40.4±10.5 years old, BMI 23.7±2.9 kg/m2) were equipped with a naso-ileal tube. They consumed for 4h nine repeated meals comprising 15N-sunflower protein biscuits together with 13C-AAs, carried either in chocolate (SUN+C, n = 7) or apple puree (SUN+P, n = 5). Ileal digesta and blood were sampled throughout 8h after ingestion of the first meal. The 15N and 13C AA enrichments were measured in digesta to determine ileal digestibility directly, and in plasma to determine lysine and threonine digestibility using the dual isotope method. Differences between methods and between vector groups were analyzed using paired and unpaired t-tests, respectively. Results Ileal digestibility of sunflower indispensable AAs (IAA) was 89±5.3%, threonine and lysine having the lowest digestibility. In the SUN+C meal, IAA digestibility was 3% below that of SUN+P (P < 0.05). Mean free 13C-AA ileal digestibility was 98.1±0.9%. No matter which matrix was used to carry 13C-AAs, plasma 15N and 13C-AA kinetics displayed a 1h offset. Digestibility obtained with the dual isotope method (70.4±6.0% for threonine and 75.9±22.3% for lysine) was below the target values. Conclusions The ileal digestibility of IAAs from a sunflower isolate incorporated in a biscuit was close to 90% in healthy adults. Under our experimental conditions, the dual isotope method provided lower values than the usual method. Further protocol developments are needed to validate the equivalence between both methods. Clinical Trial Registry The clinical trial was registered at www.clinicaltrials.gov database (NCT04024605).

Objectives In order to establish DIAAS in humans, the FAO recommended to develop a new method to measure indispensable amino acid (IAA) digestibility. This method uses two isotopic labeling, one for the protein to test and one for a reference protein. Spirulina was chosen as the 13C reference protein due to its commercial availability and affordability. However, the real digestibility of spirulina protein has not been measured in vivo. This work aims to assess the digestibility of spirulina and its repeatability in different meal tests in rats. Methods 23 Wistar male rats were fed a test meal containing 0.5 g of 15 N protein from either spirulina (n = 7), sunflower n = 8) or goat milk isolate (n = 8) and 10 mg of 13C labeled spirulina. Rats were euthanized 6 h after the meal and their digestive luminal contents (stomach, small intestine, ileum, caecum, colon) were collected. Protein digestibility was determined for the test and the reference proteins by measuring 15 N and 13C enrichments in the digesta by EA-IRMS. Caecal IAA digestibility of 13C spirulina was determined by measuring the quantity of AA in the caecum by UPLC and the 13C enrichment in AA by GC-C-IRMS. Group effects were tested using one way ANOVA and differences between groups using Bonferroni test. Results Six hours after ingestion, most of the dietary 15 N and 13C were found in the caecum and colon. But there at least twice more 15 N nitrogen in the caecum and colon in the spirulina group than in the two other groups. Therefore, spirulina protein digestibility (86.0 ± 0.7%) was lower (P < 0.001) than sunflower (95.1 ± 0.5%) and goat milk digestibility (97.2 ± 0.2%). 13C spirulina digestibility tended to be different (P = 0.06) when mixed to spirulina (90.6 ± 0.6%), sunflower (88.8 ± 0.5%) or goat milk (89.0 ± 0.5%) isolates. The caecal IAA digestibility of 13C spirulina was lower in the spirulina group than in sunflower and goat milk groups for every IAA tested, and the mean was 91.6 ± 0.2% for sunflower, 91.4 ± 0.4% for goat milk and 85.4 ± 0.6% for spirulina. Conclusions Spirulina protein is of lower digestibility than other animal or plant proteins. Protein and amino digestibility of a tracer dose of 13C spirulina appears to vary depending on the protein component of the meal. These results question the use of spirulina as a reference protein for the dual isotope method. Funding Sources French Research National Agency (ANR), SOFIPROTEOL. Supporting Tables, Images and/or Graphs

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AbstractIntroduction:Sunflower protein is not used in human nutrition despite a relatively good amino acid composition. However, the bioavailability of sunflower isolate has never been measured in Humans. The goal of this work was to determine ileal digestibility of protein and amino acids from a sunflower isolate in healthy volunteers and to challenge newly developed dual isotope method.Materials and methods:Eight healthy volunteers were equipped with a naso-ileal tube. They received during four hours twelve doses of biscuits containing, in total, 25 g of 15N sunflower protein isolate together with 400 mg of a mixture of free 13C amino acids incorporated in chocolates. Polyethylene glycol was perfused as non-absorbable marker and ileal contents were collected during 8 hours after ingestion of the first meal. Real ileal digestibility was measured by assessing nitrogen and carbon content as well as 15N and 13C enrichments by EA-IRMS. Amino acid digestibility was determined by measuring 15N and 13C enrichments by GC-C-IRMS and quantity of amino acids by UPLC. Blood was collected for 8 h to determine 15N and 13C enrichments by GC-C-IRMS.Results:The ileal nitrogen flow was 2.7 ± 0.5 mL/min (mean ± SD). In average, 53.1 ± 12.0 mmol of exogenous nitrogen was recovered during the eight hours of experiment, resulting in an ileal digestibility of sunflower isolate was 85.6 ± 2.6 % of nitrogen ingested. 13C amino acids were also recovered at the ileal level. The mixture of free 13C revealed an ileal digestibility of 94.9 ± 0.9 %. Ileal indispensable amino acids digestibility and DIAAS are in progress.Discussion:Ileal digestibility of sunflower isolate incorporated in toasted biscuits was lower than the value found or a raw isolate in a rat model (94.5%). The study revealed that 5 % of free amino acids were not absorbed in the ileum. Amino acid digestibility will complete the study to evaluate the DIAAS of sunflower isolate and to compare values obtained with the standard method and with the dual isotope method.