Digested proteins free#

Our primary end point was postprandial leucine balance. Therefore, the main objective of the present set of studies was to compare postprandial whole body protein kinetics, and mainly protein deposition, after ingestion of various protein meals having identical amino acid composition but differing only by their rate of digestion. This might have influenced the previous results and warranted further examination. However, both the total nitrogen content and the amino acid composition of the whey proteins and of the casein were different. In our previous studies, we closely controlled the leucine contents of the different meals ( 5). The amount of dietary nitrogen also affects postprandial protein anabolism. The amino acid composition of a dietary protein is a major factor affecting its biological value. However, the relative importance of protein digestion rate on protein metabolism requires further investigation. This new concept might represent an original and adjunctive dietary strategy to prevent protein losses in various pathological circumstances ( 16). Taken together, our results suggested that, in young adults, “slow” proteins (e.g., casein) fare better than “fast” proteins (e.g., whey) with respect to postprandial protein gain. Therefore, the postprandial leucine balance, an index of protein deposition, was better with casein than with whey ( 5). Most importantly, postprandial leucine oxidation was significantly higher after ingestion of whey proteins than after ingestion of casein despite identical leucine intakes. Using milk protein fractions intrinsically labeled with l- leucine, we demonstrated that whey proteins are more rapidly digested than native micellar casein. In addition, we have recently suggested the existence of a relationship between the regulation of postprandial protein kinetics and the rate of digestion and absorption of dietary proteins ( 5). Amino acid availability depends directly on both the quantity ( 17, 31) and the quality ( 30, 33) of the dietary source of nitrogen. The main regulators of these metabolic pathways are hormones, primarily insulin ( 10, 15), and substrates, primarily amino acids ( 18, 38, 40). Shifting from the postabsorptive (overnight fasting) to the fed state is characterized by protein deposition, as a result of coordinated changes in protein synthesis, breakdown, and amino acid oxidation ( 4, 17, 19, 28, 31, 33, 40). Protein digestion rate is an independent factor modulating postprandial protein deposition. Postprandial leucine balance over 7 h was higher after the slow than after the fast meals (CAS: 38 ± 13 vs.

After slow meals, these parameters increased moderately but durably. The fast meals induced a strong, rapid, and transient increase of aminoacidemia, leucine flux, and oxidation. Comparisons were made between “fast” (AA, WP) and “slow” (CAS, RPT-WP) meals of identical amino acid composition (AA vs.

Digested proteins free#

Four groups of five or six young men received an l-leucine infusion and one of the following 30-g protein meals: a single meal of slowly digested casein (CAS), a single meal of free amino acid mimicking casein composition (AA), a single meal of rapidly digested whey proteins (WP), or repeated meals of whey proteins (RPT-WP) mimicking slow digestion rate. To evaluate the importance of protein digestion rate on protein deposition, we characterized leucine kinetics after ingestion of “protein” meals of identical amino acid composition and nitrogen contents but of different digestion rates.