Martial Dangin

The rate of protein digestion affects protein gain differently during aging in humans

In young men ingesting protein meals, slowly digested proteins (caseins: CAS) induce a higher protein gain than those that are rapidly digested (whey proteins: WP). Our aim was to assess whether or not this is true in elderly men receiving mixed meals. The effects of meals containing either CAS or two different amounts of WP (WP‐iN: isonitrogenous with CAS, or WP‐iL: providing the same amount of leucine as CAS) on protein metabolism (assessed by combining oral and intravenous leucine tracers) were compared in nine healthy, elderly (mean ±s.e.m. age 72 ± 1 years) and six young men (24 ± 1 years). In both age groups, WP‐iL and WP‐iN were digested faster than CAS (P < 0.001, ANOVA). Proteolysis was inhibited similarly whatever the meal and age groups (P= NS). Protein synthesis was higher with WP‐iN than with CAS or WP‐iL (P < 0.01), irrespective of age (P= NS). An age‐related effect (P < 0.05) was found with postprandial leucine balance. Leucine balance was higher with CAS than with WP‐iL (P < 0.01) in young men, but not in elderly subjects (P= NS). In isonitrogenous conditions, leucine balance was higher with WP‐iN than with CAS (P < 0.001) in both age groups, but the magnitude of the differences was higher in the elderly men (P= 0.05). In conclusion, during aging, protein gain was greater with WP (rapidly digested protein), and lower with CAS (slowly digested protein). This suggests that a ‘fast’ protein might be more beneficial than a ‘slow’ one to limit protein losses during aging.

Rapid and accurate13CO2isotopic measurement in whole blood: comparison with expired gas

Determination of 13CO2 enrichment on the CO2 released from blood by acid has been used in situations in which breath sampling is difficult. This method can be improved by measuring this enrichment on the CO2 spontaneously released from blood. Therefore, simultaneous comparisons of 13CO2 content between breath and arterialized blood added with or without acid were performed in 51 samples from human studies, using the statistical method of Bland and Altman (J. M. Bland and D. G. Altman. Lancet 1: 307-310, 1986). Strong relationships exist between the methods (r > 0.99) expressed in atom percent excess (APE). Compared with breath, the acid method overestimates the 13CO2 enrichment (0.318 +/- 0.632 APE x 1,000, P < 0.001). The acid-free method shows similar enrichments to breath (0. 003 +/- 0.522 APE x 1,000, P = 0.97) with good precision and degree of agreement (95% confidence interval 0.15 APE x 1,000). The analysis can be performed up to 5 days after sampling with a good reproducibility. In conclusion, measuring 13CO2 enrichments on the CO2 spontaneously released from blood is feasible, gives identical results to the breath method, and lessens operator manipulations. It allows study of situations in which the breath sampling method is not feasible.Determination of13CO2enrichment on the CO2 released from blood by acid has been used in situations in which breath sampling is difficult. This method can be improved by measuring this enrichment on the CO2 spontaneously released from blood. Therefore, simultaneous comparisons of13CO2content between breath and arterialized blood added with or without acid were performed in 51 samples from human studies, using the statistical method of Bland and Altman (J. M. Bland and D. G. Altman. Lancet 1: 307-310, 1986). Strong relationships exist between the methods ( r > 0.99) expressed in atom percent excess (APE). Compared with breath, the acid method overestimates the13CO2enrichment (0.318 ± 0.632 APE × 1,000, P < 0.001). The acid-free method shows similar enrichments to breath (0.003 ± 0.522 APE × 1,000, P = 0.97) with good precision and degree of agreement (95% confidence interval 0.15 APE × 1,000). The analysis can be performed up to 5 days after sampling with a good reproducibility. In conclusion, measuring13CO2enrichments on the CO2spontaneously released from blood is feasible, gives identical results to the breath method, and lessens operator manipulations. It allows study of situations in which the breath sampling method is not feasible.