Association of postprandial postexercise muscle protein synthesis rates with dietary leucine: A systematic review

Abstract

BackgroundDietary protein ingestion augments post (resistance) exercise muscle protein synthesis (MPS) rates. It is thought that the dose of leucine ingested within the protein (leucine threshold hypothesis) and the subsequent plasma leucine variables (leucine trigger hypothesis; peak magnitude, rate of rise, and total availability) determine the magnitude of the postprandial postexercise MPS response.MethodsA quantitative systematic review was performed extracting data from studies that recruited healthy adults, applied a bout of resistance exercise, ingested a bolus of protein within an hour of exercise, and measured plasma leucine concentrations and MPS rates (delta change from basal).ResultsIngested leucine dose was associated with the magnitude of the MPS response in older, but not younger, adults over acute (0–2 h, r2 = 0.64, p = 0.02) and the entire postprandial (>2 h, r2 = 0.18, p = 0.01) period. However, no single plasma leucine variable possessed substantial predictive capacity over the magnitude of MPS rates in younger or older adults.ConclusionOur data provide support that leucine dose provides predictive capacity over postprandial postexercise MPS responses in older adults. However, no threshold in older adults and no plasma leucine variable was correlated with the magnitude of the postexercise anabolic response.

Ingestion of a variety of non-animal-derived dietary protein sources results in diverse postprandial plasma amino acid responses which differ between young and older adults

“…( 5 , 12 – 15 , 45 ) ). This body of work has shown that various crucial aspects are to be considered, including the (essential) amino acid composition of a protein source ( 3 , 4 ) , the postprandial rise in circulating insulin concentrations ( 46 , 47 ) , as well as the postprandial peak concentration (Tmax), time to reach peak concentration (Cmax) and total availability (iAUC) of circulating EAAs (particularly leucine) once ingested ( 5 , 6 , 45 , 48 ) , though the ultimate anabolic response is complex and driven by the interplay between these factors ( 49 ) . Bearing these variables in mind, such studies have established what constitutes a ‘high-quality’ dietary protein, with obvious examples in work examining milk proteins ( 50 – 52 ), and, more recently, we identified fungal-derived mycoprotein as a similarly high-quality non-animal-derived protein ( 30 – 33 ) .…”

Celebrating a decade of exercise physiology and metabolism research in physiological reports

“…Adaptations to exercise are governed not only by the mode, duration, and intensity of exercise itself but are also heavily influenced by postexercise nutrition (Wilkinson et al., 2023). For example, protein intake following resistance exercise is known to increase muscle protein synthesis.…”

Reconsidering the pre-eminence of dietary leucine and plasma leucinemia for predicting the stimulation of postprandial muscle protein synthesis rates

“…Although this requirement likely fulfills substrate requirements, it may not be optimal for signaling purposes, and the per meal “signaling requirement” is often proposed to be 2–3 g of ingested leucine (∼35 mg/kg body mass), implying this latter role may be more limited from a dietary intake perspective. Although the quantity of leucine ingested as a “signal” strongly predicts the appearance in plasma [ 43 ], it is unclear to what extent it predicts a rise in extra/intra (myo)cellular leucine, and it should also be considered that most studies do not allow the disentanglement of leucine’s signaling role from leucine-independent signaling pathways involved in translation initiation.…”

“…Given the interpretative difficulties contained within single studies discussed above, 2 recent systematic reviews have attempted to amalgamate decades of data to evaluate the extent to which ingested leucine dictates MPS [ 43 , 58 ]. Zaromskyte et al.…”

“…Worthy of note, however, is their approach revealed only around half of the studies included were supportive of the hypothesis, and its utility was restricted primarily to older adults (mostly postexercize) and only to the ingestion of isolated protein sources [ 58 ]. Intrigued by these findings, we recently conducted a quantitative systematic review [ 43 ]. This allowed us to report direct correlations between the key variables, which we interpreted as the distinct predictive capacities of the leucine trigger hypothesis on postprandial (and postexercize) MPS rates (notwithstanding the possibility of reverse causation).…”