Effect of increased protein intake on renal acid load and renal hemodynamic responses

Abstract

Increased protein intake versus maltodextrin intake for 4 weeks lowers blood pressure. Concerns exist that high-protein diets reduce renal function. Effects of acute and 4-week protein intake versus maltodextrin intake on renal acid load, glomerular filtration rate and related parameters were compared in this study. Seventy-nine overweight individuals with untreated elevated blood pressure and normal kidney function were randomized to consume a mix of protein isolates (60 g/day) or maltodextrin (60 g/day) for 4 weeks in energy balance. Twenty-four-hour urinary potential renal acid load (uPRAL) was compared between groups. A subgroup (maltodextrin N = 27, protein mix N = 25) participated in extra test days investigating fasting levels and postprandial effects of meals supplemented with a moderate protein- or maltodextrin-load on glomerular filtration rate, effective renal plasma flow, plasma renin, aldosterone, pH, and bicarbonate. uPRAL was significantly higher in the protein group after 4 weeks (P ≤ 0.001). Postprandial filtration fraction decreased further after the protein-supplemented breakfast than after the maltodextrin-supplemented breakfast after 4 weeks of supplementation (P ≤ 0.001). Fasting and postprandial levels of glomerular filtration rate, effective renal plasma flow, renin, aldosterone, angiotensin-converting enzyme, pH and bicarbonate did not differ between groups. In conclusion, 4 weeks on an increased protein diet (25% of energy intake) increased renal acid load, but did not affect renal function. Postprandial changes, except for filtration fraction, also did not differ between groups. These data suggest that a moderate increase in protein intake by consumption of a protein mix for 4 weeks causes no (undesirable) effects on kidney function in overweight and obese individuals with normal kidney function.

Keywords: Acid load; carbohydrate; glomerular filtration rate; kidney; protein.

Figure 1

Mean (±SEM) of 4‐h postprandial responses of renal function to breakfasts supplemented with protein or maltodextrin on day 1 of supplementation (left) and after 4 weeks of supplementation (right). Panels are ERPF (A, B), GFR (C, D), FF (E, F), and RVR (G, H). On day 1 ERPF, GFR and FF n = 25 maltodextrin group, n = 25 protein group; RVR n = 24 maltodextrin group, n = 24 protein group. After 4 weeks ERPF, GFR, FF, and RVR n = 26 maltodextrin group, n = 24 protein group. *P < 0.05 for the difference between maltodextrin group (black) and protein group (white) over the whole 4‐h period according to the mixed model. ERPF, effective renal plasma flow; FF, filtration fraction; GFR, glomerular filtration rate; RVR, renal vascular resistance.

Figure 2

Mean (±SEM) of 12 h postprandial responses of renin‐angiotensin‐aldosterone system to meals supplemented with protein or maltodextrin on day 1 of supplementation (left) and after 4 weeks of supplementation (right). Panels are renin (A, B) and aldosterone (C, D). On day 1 renin n = 25 maltodextrin group, n = 25 protein group; aldosterone n = 27 maltodextrin group, n = 25 protein group. After 4 weeks renin and aldosterone n = 27 maltodextrin group, n = 25 protein group. Vertical lines indicate breakfast, lunch, and dinner. *P < 0.05 for the difference between maltodextrin group (black) and protein group (white) over the whole 12‐h period according to the mixed model.

Figure 3

Mean (±SEM) of 12 h postprandial responses of blood pH and bicarbonate to meals supplemented with protein or maltodextrin on day 1 of supplementation (left) and after 4 weeks of supplementation (right). Panels are pH (A, B) and bicarbonate (C, D). On day 1 and after 4 weeks pH and bicarbonate n = 26 maltodextrin group, n = 25 protein group. Vertical lines indicate breakfast, lunch, and dinner. Postprandial responses did not differ between the maltodextrin group (black) and protein group (white) according to the mixed model.

Figure 4

Mean (±SEM) of 24‐h uPRAL (panel A) and ammonium excretion (panel B) at baseline and after 4 weeks of supplementation in the protein group (white) and maltodextrin group (black). For uPRAL: baseline n = 41 maltodextrin group, n = 35 protein group. After 4 weeks n = 38 maltodextrin group, n = 35 protein group. For ammonium: baseline n = 43 maltodextrin group, n = 35 protein group. After 4 weeks n = 39 maltodextrin group, n = 35 protein group. Between‐group differences on day 0 were tested with an independent samples t‐test. Between‐group differences after 4 weeks were tested with ANCOVA correcting for the fasting value on day 0. uPRAL, urinary potential renal acid load.