4. Discussion
bloating, nausea, gastrointestinal symptoms, flatulence, diarrhea, shakes, constipation, TAA
We evaluated, in a double-blind, cross-over intervention trial, the postprandial AA uptake of protein from BRP and compared this response to PP and the benchmark protein WP. Differences in postprandial plasma TAA kinetics were observed between BRP, PP, and WP, with WP giving the highest response, followed by the two other protein sources. When looking at postprandial plasma TEAA confidence intervals, the response after BRP shake consumption was slightly lower when compared to PP. The time to reach the maximum values was similar between the three protein sources. Seven out of nine EAA showed higher postprandial responses after WP shake consumption when compared to BRP. BRP shake consumption did result in a higher uptake of the Phe when compared to WP. When comparing individual EAA responses between BRP and PP, we observed higher responses in methionine (Met) and tryptophane (TRP) and lower responses in lysine (Lys), histidine (His), and isoleucine (Ile) after BRP shake consumption when compared to PP. The estimated TAA uptake of BRP, as determined by comparing the calculated iAUC, is 69% compared to the benchmark WP. The EAA uptake of BRP is somewhat lower, with an estimated relative uptake of 58% compared to WP. Plant proteins exhibit reduced digestibility due to the presence of indigestible fractions within their sequence as well as the presence of anti-nutritional factors [Previously, we conducted a comparable study on postprandial AA uptake investigating Lemna protein concentrate. In that publication, we also reported an overview of the available literature data on iAUC values of EAA uptake from other protein sources in a human cross-over design with whey protein as the benchmark [Statistically significant differences were not observed when examining the iAUC of the TAA for the two plant proteins investigated in this study. We did, however, observe a slightly greater overall response in TEAA following the consumption of the PP shake compared to the BRP shake. Even though the iAUC of TEAA for BRP was approximately 82% in comparison to PP, certain individual EAA clearly exhibited higher responses for BRP. Furthermore, no significant differences in the peak heights of TAA and TEAA were observed between BRP and PP. BRP has been shown to have substantially higher solubility in comparison to pea protein, with on average 102% (expressed as total protein percentage remaining in a 1% solution) and 22%, respectively, making BRP nearly five times more soluble than PP [Next to the lower overall uptake rates of plant proteins, the absorption speed of plant proteins may also be delayed. For instance, higher time-2-max values of the TAA and TEAA responses were observed in a previous study with corn protein isolate (manuscript in preparation) and Lemna protein concentrate [This study provides valuable insights into the potential absorption rates of individual EAA. When a particular EAA is limited in availability in the diet, the synthesis of protein is hampered [Since whey is considered a protein source with an optimal EAA composition and easy to digest [Uptake scores of individual EAA of BRP, estimated by comparing the iAUC, were in a higher (Met, Trp), similar (Val, Thr, Phe, Leu), or lower (Lys, His, Ile) range compared to PP. The higher postprandial uptake levels of Met and lower levels of Lys after consumption of the BRP shake were expected. This is because the AA composition of pea, in general, is characterized by a limited content of Met [Despite the significantly higher Glu content in BRP compared to PP and WP, as well as in relation to other AA, there was no significant difference observed in the postprandial iAUC of Glu among the three protein shakes. Additionally, the iAUC of Glu in relation to its presence in the product was generally low compared to other AA. One plausible explanation for the low concentration of Glu in the bloodstream is the high energy demand of the small intestine epithelium, particularly in the postprandial state. Consequently, Glu is either directly utilized or taken up from the bloodstream for extensive oxidation within the cells of the small intestine epithelium [In the current study, participants assessed their general health and reported their experiences of bloating, nausea, occurrence of belching, flatulence, diarrhea, and constipation using an online questionnaire after each test day. The occurrence of these gastrointestinal symptoms was minimal and did not significantly differ among the three protein shakes. This indicates that the consumption of 20 g BRP per day was well-tolerated. Despite having an equivalent carbohydrate composition, differences were observed in the postprandial insulin and glucose responses among the protein shakes. Consumption of the BRP shake, although not significant, led to a reduced peak in insulin levels, while the peak in glucose levels was comparable to that of the PP shake. This may be partly explained by differences in the type of carbohydrates, as WP and PP contained added maltodextrin to match the higher carbohydrate content of BRP. The breakdown of proteins into AA triggers an insulin response, and indeed, a rapid surge in insulin was observed shortly after protein ingestion. The purpose of this insulin surge is to facilitate the transportation of AA into the muscles, thereby stimulating muscle protein synthesis [The evaluation of protein digestibility and nutritional characteristics of emerging sustainable protein sources poses challenges, particularly when avoiding animal experiments. The gold standard methodologies for assessing digestibility, namely the protein digestibility-corrected AA score, PDCAAS, and the more recent digestible indispensable AA score, DIAAS [