Abstract
Dietary protein digestion and amino acid absorption kinetics determine the post-prandial muscle protein synthetic response. Body position may affect gastrointestinal function and modulate the post-prandial rise in plasma amino acid availability. We aimed to assess the impact of body position on gastric emptying rate and the post-prandial rise in plasma amino acid concentrations following ingestion of a single, meal-like amount of protein. In a randomized, cross-over design, eight healthy males (25 ± 2 years, 23.9 ± 0.8 kg·m−2) ingested 22 g protein and 1.5 g paracetamol (acetaminophen) in an upright seated position (control) and in a −20° head-down tilted position (inversion). Blood samples were collected during a 240-min post-prandial period and analyzed for paracetamol and plasma amino acid concentrations to assess gastric emptying rate and post-prandial amino acid availability, respectively. Peak plasma leucine concentrations were lower in the inversion compared with the control treatment (177 ± 15 vs. 236 ± 15 mmol·L−1, p < 0.05), which was accompanied by a lower plasma essential amino acid (EAA) response over 240 min (31,956 ± 6441 vs. 50,351 ± 4015 AU; p < 0.05). Peak plasma paracetamol concentrations were lower in the inversion vs. control treatment (5.8 ± 1.1 vs. 10.0 ± 0.6 mg·L−1, p < 0.05). Gastric emptying rate and post-prandial plasma amino acid availability are significantly decreased after protein ingestion in a head-down tilted position. Therefore, upright body positioning should be considered when aiming to augment post-prandial muscle protein accretion in both health and disease.
Highlights
Ingestion of dietary protein increases muscle protein synthesis rates [1–5]. This increase in muscle protein synthesis has been attributed to the post-prandial rise in circulating amino acid concentrations, with leucine being of particular relevance [6–9]
Differences in the anabolic properties of various proteins have been attributed to their specific protein digestion and amino acid absorption kinetics [21], as well as their amino acid composition [22]
Previous work from our group [16] as well as others [3,23–29] has shown that the ingestion of more rapidly digestible protein, such as whey, results in a greater post-prandial rise in circulating amino acid concentrations, thereby further increasing whole body and/or muscle protein synthesis rates when compared with the ingestion of a more slowly digestible protein, such as intact casein
Summary
Ingestion of dietary protein increases muscle protein synthesis rates [1–5]. This increase in muscle protein synthesis has been attributed to the post-prandial rise in circulating (essential) amino acid concentrations, with leucine being of particular relevance [6–9]. Differences in the anabolic properties of various proteins have been attributed to their specific protein digestion and amino acid absorption kinetics [21], as well as their amino acid composition [22]. Previous work from our group [16] as well as others [3,23–29] has shown that the ingestion of more rapidly digestible protein, such as whey, results in a greater post-prandial rise in circulating amino acid concentrations, thereby further increasing whole body and/or muscle protein synthesis rates when compared with the ingestion of a more slowly digestible protein, such as intact casein. Whey and casein do differ in their protein digestion and absorption kinetics, and in their amino acid composition, with whey containing more leucine [11,24,27]
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