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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Nutrient Ingestion, Protein Intake, and Sex, but Not Age, Affect the Albumin Synthesis Rate in Humans^1–3,

⁴ Department of Foods and Nutrition, Purdue University, West Lafayette, IN 47906; ⁵ Department of Mathematics, Brigham Young University-Idaho, Rexburg, ID 83460; and ⁶ Department of Internal Medicine, Washington University, St. Louis, MO 63110

^* To whom correspondence should be addressed. E-mail: campbellw{at}purdue.edu.

The aim of this study was to assess the effects of nutrient ingestion, dietary protein intake, age, and sex on the fractional synthesis rate (FSR) of albumin. Thirty-six healthy free-living individuals (8 females and 10 males aged 21–43 y and 9 females and 9 males aged 63–79 y) completed three 18-d periods of controlled feeding with protein intakes of 125% (P125, 1.00 g protein · kg^–1 · d^–1), 94% (P94, 0.75 g protein · kg^–1 · d^–1), and 63% (P63, 0.50 g protein · kg^–1 · d^–1) of the recommended dietary allowance. On d 12 of each trial, postabsorptive (PA) serum albumin concentration was determined and PA and postprandial (PP) albumin FSR were estimated from the rate of L-[1-¹³C] leucine incorporation into plasma albumin during an 8-h infusion. There were no age-related differences in PA and PP albumin FSR. Albumin FSR was higher PP than PA (P < 0.0001), and the increase in albumin FSR from PA to PP was smaller as dietary protein intake decreased from P125 to P94 and P63 (P < 0.05). Independent of protein intake, males had a higher albumin FSR (P < 0.05) and a greater increase in albumin FSR with feeding (P < 0.05). There was no age or dietary protein effect on serum albumin concentrations, but males had higher albumin concentrations than females (P < 0.0001). These results show that older persons are responsive to nutrient ingestion and dietary protein-related changes in albumin FSR. The greater albumin synthesis rate in males might contribute to a higher albumin concentration set point.