Background
Ingestion of protein concentrates and isolates increases muscle protein synthesis rates, with exercise further augmenting the anabolic response to feeding. However, far less information is available on the muscle protein synthetic response following ingestion of (dairy) wholefoods. Our objective was to assess the impact of ingesting 30g protein provided as quark on in vivo muscle protein synthesis rates at rest and after exercise in both young and older males.

Methods
In this parallel-group intervention trial, fourteen healthy, young (24±5 y; BMI 24.0±3.5 kg/m²) and fifteen healthy, older (73±3 y; BMI 24.2±2.4 kg/m²) males ingested 291g quark (30g protein, 693 kJ) following a single-legged bout of resistance-type exercise on leg press and leg extension machines. Primed, continuous intravenous L-[ring-¹³C₆]-phenylalanine infusions were combined with the collection of blood and muscle tissue samples to assess postabsorptive and 4-h postprandial muscle protein synthesis rates at rest and after exercise. Data represent means±SD; η² was used for effect size.

Results
Plasma leucine and total amino acid concentrations increased following quark ingestion, peaked at t= 1 h in both groups, and returned to postabsorptive concentrations at t= 4 h (both Time: P<0.001; η²>0.8), with no differences between groups (both Time*Group: P>0.1; η²<0.1). Muscle protein synthesis rates increased following quark ingestion at rest in both young (from 0.030±0.011 to 0.051±0.011 %/h) and older males (from 0.036±0.011 to 0.062±0.013 %/h), with a further increase in the exercised leg (to 0.071±0.023 %/h and to 0.078±0.019 %/h, respectively; Condition: P<0.001; η²=0.716), with no differences between groups (Condition*Group: P>0.1; η²=0.011).

Conclusions
Quark ingestion increases muscle protein synthesis rates at rest with a further increase after exercise in both young and older males. The muscle protein synthetic response following fermented dairy ingestion does not differ between healthy, young and older males when ample amounts of protein (30g) are ingested.

This collaboration project is co-funded by FrieslandCampina BV, and the PPP Allowance made available by Health-Holland, Top Sector Life Sciences & Health, to stimulate public-private partnerships.