Essential Amino Acid Supplementation Enhances Post-prandial Amino Acid Availability Following a Standard-protein Breakfast in Older Adults: a Randomised Crossover Trial

Sarcopenia refers to a skeletal muscle disorder via loss of muscle strength, mass and function that naturally progresses with age. More recently however, the phenomenon of acute sarcopenia (AS) has been suggested which refers to sarcopenia that occurs within a period of six months. This rapid deterioration of muscle, which typically occurs as a result of an illness or stressor, significantly increases the risk of hospital admission, loss of independence, and mortality making it an important target for future research.

Poor nutrition and specifically inadequate energy and dietary protein intakes are contributors to the development of both sarcopenia and AS. Therefore, addressing energy and protein deficiencies have been proposed in review papers as a means to prevent and/or better manage sarcopenia and AS. This is not something that has been explicitly investigated within this specific clinical population to date. Nutritional interventions which are focused on addressing total energy and protein deficiencies will optimise skeletal muscle adaptations via essential amino acids, particularly Leucine, found in protein acting as an important anabolic stimulus for the mammalian target of rapamycin (mTOR). Therefore, this type of management strategy should be able to attenuate the muscle wasting and exacerbated life outcomes (mortality, loss of independence, frailty) that occurs in AS and among other serious health conditions.

Older populations require approximately 30-40g of protein per meal ( ̴0.45 g/kg/BM/Day), with particular importance of leucine, in order to achieve recent recommended daily amounts of 1.2-1.6g/kg/BM/day but this is difficult to achieve in the older population which naturally suffers from a reduced appetite and increased perception of fullness. Breakfast and lunch commonly suffer from the greatest deficiency in protein intake and Ispoglou et al. have developed effective ways in which to increase dietary protein intake without affecting hunger.

The gels which Ispoglou et al. have developed contain 7.5g of essential amino acids (EAAs) per sachet of 65 ml volume each, the equivalent found in 15g of high-quality protein (3g of leucine), and the addition of one of these gels alongside a meal could potentially assist older adults to reach optimal protein requirements on a per meal and daily basis. Previously, supplementation with EAAs has shown to be effective in increasing functional performance and lean tissue mass, while it has been proposed as a potential nutritional therapy for addressing sarcopenia. These EAA gels also do not affect appetite in older adults and have been shown to be an effective means for enhancing both protein and energy intake in older adults.

Supplementation with such gels, as we have shown, can increase plasma concentrations of essential amino acids (AAs), such as leucine, which in turn can act as anabolic stimuli and enhance muscle protein synthesis and potentially prevent or minimise muscle wasting. Plasma concentrations of amino acids, in particular leucine, drives muscle protein synthesis however an excessive concentration of leucine can increase oxidation rates of other essential amino acids, in particular L-isoleucine and L-valine, meaning there is lower plasma availability for muscle protein synthesis. Thus, it is important to identify which AA ratio can maximise the potential for muscle protein synthesis rather than increase oxidation of AAs and limit muscle protein synthesis.