Abstract
Industrial heat treatment of milk results in protein glycation. A high protein glycation level has been suggested to compromise the post-prandial rise in plasma amino acid availability following protein ingestion. In the present study, we assessed the impact of glycation level of milk protein on post-prandial plasma amino acid responses in humans. Fifteen healthy, young men (age 26 (SEM 1) years, BMI 24 (SEM 1) kg/m2) participated in this randomised cross-over study and ingested milk protein powder with protein glycation levels of 3, 20 and 50 % blocked lysine. On each trial day, arterialised blood samples were collected at regular intervals during a 6-h post-prandial period to assess plasma amino acid concentrations using ultra-performance liquid chromatography. Plasma essential amino acid (EAA) concentrations increased following milk protein ingestion, with the 20 and 50 % glycated milk proteins showing lower overall EAA responses compared with the 3 % glycated milk protein (161 (SEM 7) and 142 (SEM 7) v. 178 (SEM 9) mmol/l × 6 h, respectively; P ≤ 0·011). The lower post-prandial plasma amino acid responses were fully attributed to an attenuated post-prandial rise in circulating plasma lysine concentrations. Plasma lysine responses (incremental AUC) following ingestion of the 20 and 50 % glycated milk proteins were 35 (SEM 4) and 92 (SEM 2) % lower compared with the 3 % glycated milk protein (21·3 (SEM 1·4) and 2·8 (SEM 0·7) v. 33·3 (SEM 1·7) mmol/l × 6 h, respectively; P < 0·001). Milk protein glycation lowers post-prandial plasma lysine availability in humans. The lower post-prandial availability of lysine following ingestion of proteins with a high glycation level may compromise the anabolic properties of a protein source.
Highlights
Ingestion of dietary protein directly stimulates muscle protein synthesis rates[1,2,3]
The integrated plasma lysine responses were significantly different between treatments (P < 0·001), with the Incremental AUC (iAUC) following ingestion of the 20 and 50 % GLYC being 35 (SEM 4) % and 92 (SEM 2) % lower when compared with the 3 % GLYC (21·3 (SEM 1·4) and 2·8 (SEM 0·7) v. 33·3 (SEM 1·7) mmol/l × 6 h, respectively; P < 0·001; Fig. 4(b))
Ingestion of milk protein powder with a moderate (20 %) to high (50 %) glycation level resulted in an attenuated rise in plasma essential amino acid (EAA) concentrations when compared with the ingestion of milk protein with a low (3 %) glycation level
Summary
Ingestion of dietary protein directly stimulates muscle protein synthesis rates[1,2,3] This anabolic response is regulated at various levels, starting from protein digestion, the absorption of free amino acids in the gastrointestinal tract, their partial release into the systemic circulation, the uptake of amino acids in skeletal muscle tissue, changes in intramyocellular signalling and eventually incorporation of amino acids into muscle proteins, that is, muscle protein synthesis[4,5]. There are currently no data available on whether the level of protein glycation modulates the post-prandial plasma amino acid response in humans
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