Re-evaluation of the Muscle-full Effect During Continuously Elevated Amino Acid Availability in Healthy Young Males

Re-evaluation of the Muscle-full Effect During Continuously Elevated Amino Acid Availability in Healthy Young Males

Muscle tissue consists of proteins. These proteins are built up of a collection of smaller building blocks: amino acids. When protein is consumed, it gets digested and absorbed into the blood. The body can use these amino acids, by taking them up from thecirculation. By consuming sufficient protein through our diet, we ensure that the body is provided with enough amino acids to enable muscle protein building. Sufficient muscle protein synthesis is important for maintaining muscle function and strength.

Previous research has shown that when 20 to 25g of protein is eaten, muscle protein synthesis is maximized. It is therefore recommended to eat 20g of protein per meal. However, it is currently unclear what happens to muscle protein synthesis rates if multiple meals are eaten. When multiple meals are consumed, amino acids appear in the circulation for prolonged period of time.

Theoretically, when there are a high amino acid concentrations in the blood, muscle protein synthesis rates will increase. Contrary to this theory, a study more than 20 years ago showed otherwise. It was observed that muscle protein synthesis rates are only elevated for2 hours afterwhich they decrease again. This phenomenon was referred to as the "muscle-full" effect. Because this phenomenon is in contrast with more previous studies, the objective is to replicate that study. This is important so that nutritional advice for healthy, but also clinical populations in the future can be improved.

Inclusion Criteria:

• Male sex
• Aged between 18 - 35 years
• Healthy (assessed based on routine medical questionnaire)
• BMI between 18.5 - 30 kg/m2

Exclusion Criteria:

A potential subject who meets any of the following criteria will be excluded from participation in this study:

• Smoking
• Involved in progressive exercise training
• A history of neuromuscular problems
• Use of anticoagulants
• Recent (<12 months) participation in amino acid tracer (L-[ring-13C6] phenylalanineand L-[3,5-2H2]-tyrosine) studies
• Use of medication known to affect (muscle) protein metabolism (e.g. corticosteroids, non-steroidal anti-inflammatory drugs, acne medication)
• Phenylketonuria
• Diagnosed with or history of liver damage
• Diagnosed with or history of severe kidney damage and/or malfunction
• Diagnosed with inability to break down amino acids