In the elderly, meat protein assimilation from rare meat is lower than that from meat that is well done

Background: Meat cooking conditions in in vitro and in vivo models have been shown to influence the rate of protein digestion, which is known to affect postprandial protein metabolism in the elderly. Objective: The present study was conducted to demonstrate the effect of cooking conditions on meat protein assimilation in the elderly. We used a single-meal protocol to assess the meat protein absorption rate and estimate postprandial meat protein utilization in elderly subjects. Design: The study recruited 10 elderly volunteers aged 70–82 y. Each received, on 2 separate occasions, a test meal exclusively composed of intrinsically ¹⁵N-labeled bovine meat (30 g protein), cooked at 55°C for 5 min [rare meat (RM)] or at 90°C for 30 min [fully cooked meat (FCM)], and minced. Whole-body fluxes of leucine, before and after the meal, were determined with the use of a [1-¹³C]leucine intravenous infusion. Meat protein absorption was recorded with the use of ¹⁵N enrichment of amino acids. Results: Postprandial time course observations showed a lower concentration in the plasma of indispensable amino acids (P < 0.01), a lower entry rate of meat leucine in the plasma (P < 0.01), and a lower contribution of meat nitrogen to plasma amino acid nitrogen (P < 0.001), evidencing lower peripheral bioavailability of meat amino acids with RM than with FCM. This was associated with decreased postprandial whole-body protein synthesis with RM than with FCM (40% compared with 56% of leucine intake, respectively; P < 0.01). Conclusions: Whereas meat cooking conditions have little effect on postprandial protein utilization in young adults, the present work showed that the bioavailability and assimilation of meat amino acids in the elderly is lower when meat is poorly cooked. In view to preventing sarcopenia, elderly subjects should be advised to favor the consumption of well-cooked meat. This trial was registered at clinicaltrials.gov as NCT02157805.