Effect of High-Protein Diet on the Glomerular Filtration Rate in the Adult and the Elderly

A high-protein meal causes an increase in the glomerular filtration rate (GFR) and can be used to assess renal functional reserve. Renal function can be affected by aging. This study was aimed at assessing GFR and renal functional reserve in healthy elderly Thais in comparison with young adults. Twenty elderly subjects aged 60-80 years, and 20 young subjects aged 20-30 years, were recruited ; each group included 10 males and 10 females. A 24 hour urine specimen was collected from each subject. Venous blood was drawn to measure serum creatinine concentration. Creatinine clearance, which represented GFR, was calculated. Each subject consumed a meal containing 1.5 grams of protein per kg BW. Urine and blood specimens were collected at 30, 60, 90, 120, 180 and 240 minutes after the meal for GFR assessment. The results showed that the elderly had a lower GFR compared with the young (70.8 ± 14.5 vs 85.6 ± 16.2 ml/min/1.73 m2). A high-protein meal caused an increase in GFR of 155 ± 63 per cent in the young and 88 ± 49 per cent in the aged. In conclusion, healthy elderly subjects showed a lower GFR and less renal functional reserve compared with young adults