Soy-based renoprotection

Table 5 Single meal intervention studies of soy protein and kidney function

Ref.	Study design	Kidney Function	Subjects/group	Amount of soy protein used	Control/comparator protein	Duration of intervention	Outcomes	Notes
Bilo et al[122]	Single meal intervention study (crossover)	Normal healthy subjects	6 normal subjects; 5 M, 1 F	Studies in normal subjects only: 80 g soy protein in single oral administration	Studies in normal subjects only: 80 g lactoprotein or beef protein or 36 g amino acids	Normal subjects: 8 individual renal function tests run on separate days	Soy protein ingestion induced significantly lower rises in GFR and ERPF compared to beef protein but not compared to lactoprotein or 36 g amino acid ingestion	Subjects with chronic renal insufficiency (PKD, NS, or MGP) were studied in a separate series of experiments in this publication, but were not used to evaluate soy protein
Buzio et al[127]	Single meal intervention study (crossover)	Normal healthy subjects	7 (gender not specified)	80 g (0.9-1.3 g.kg BW)	80 g red meat or 80 g dairy (cheese)	Single meal interventions conducted 1 wk apart	CrCl and urinary protein were not different between protein loads	Publication describes 2 separate experiments; soy protein effects on renal function only assessed in second experimental protocol
							UAp was significantly lower after soy protein meal versus red meat or cheese meals (P < 0.01) (samples taken 4 h post-meal)
							Water excretion rate was higher after soy protein load versus meat (P < 0.05) or cheese (P < 0.01)
							Serum total protein was lower after soy protein load compared to meat (P < 0.01) or cheese (P < 0.01) loads
Deibert et al[126]	Single meal intervention study (crossover)	Normal healthy and metabolic syndrome subjects; all with normal kidney function	10 subjects per group (All males)	1st intervention: 1 g/kg/BW soy protein: Milk protein (83% soy protein);	N/A	Single meal intervention in normal healthy subjects; 2 meal interventions in subjects with metabolic syndrome (1 wk apart)	Patients with metabolic syndrome had significantly elevated baseline GFR and ERPF compared to healthy subjects (P = 0.02)	0.3 g/kg/BW is amount of protein used in meal replacement therapy
				2nd intervention same protein source at 0.3 g/kg BW			After ingestion of 1 g/kg/BW protein, GFR and ERPF increased in both groups however the subjects with metabolic syndrome had significantly higher increases in GFR (P < 0.002) and ERPF (P < 0.02) compared to normal subjects; no significant effect of ingestion of 0.3 g/kg per BW protein on renal parameters in subjects with metabolic syndrome
Howe et al[118]	Single meal intervention study (Latin square crossover)	Healthy PM women	8 F subjects	45 g soy protein	0 g protein, 45 g beef or dairy protein (cottage cheese)	Single meal intervention; 6 meal interventions (1 wk apart)	Urinary Ca excretion was significantly greater after 45 g protein meal for all proteins compared to basal (0 g protein) meal (P < 0.05)
							% Ca resorbed by the kidney was significantly reduced after the dairy and soy protein meals (P < 0.05)
							Serum ionized Ca was unaffected, however, serum P was significantly lowered by all protein meals (P < 0.05) compared to 0 g protein meal
							Soy protein meal significantly reduced calcitonin versus baseline (P < 0.05) however, all protein means tended to lower calcitonin compared to baseline
							Dairy protein significantly increased PTH (P < 0.05) compared to baseline, however all protein meals tended to elevate PTH compared to baseline
							Serum insulin was significantly increased by all protein meals (over time) compared 0 g protein meal (P < 0.05)
Kontessis et al[70]	Single meal intervention study (crossover)	Normal healthy subjects	7 M subjects	80 g soy protein	80 g lean beef	2 separate single meal interventions	GFR and ERPF increased significantly after acute beef protein load (P < 0.005 compared to baseline) but did not increase with soy protein load	Amount of soy protein in vegetable protein diet in the reported chronic study was not specified so is therefore not summarized
							Renal vascular resistance fell significantly after beef load (P < 0.05) but was unchanged after soy protein load; plasma 6-keto-PGF1α rose significantly after meat load (P < 0.05) but not after soy protein load
							Fractional albumin and IgG clearance rose after beef load (P < 0.05 and P < 0.001, respectively) but did not change significantly after soy protein load; plasma protein concentrations were not different between different protein loads; UAp was not different between groups
							Plasma glucagon increase was higher after meat load (P < 0.05) compared to soy protein load; no differences were seen between proteins on plasma insulin or growth hormone
Nakamura et al[123]	Single meal intervention study (crossover)	Healthy and T2D subjects (T2D divided into 3 groups based on AER: Group A ≤ 20 μg/min (Normal); B = 20-200 μg/min; C ≥ 200 μg/min	11 healthy subjects (8M, 3F); 20 T2D patients (10 M, 10 F)	1g/kg soy protein (as bean curd)	1 g/kg tuna fish protein	Meals fed on separate days	In healthy subjects, eGFR increased (P < 0.01) after tuna meal but no significant difference after soybean curd meal
							In Grp A, eGFR increased with tuna meal (P < 0.01) but not after soybean curd
							In Group B there was no difference in GFR with either protein
							In group C, GFR sig decreased after tuna meal (P < 0.05) but not with soy protein
							No changes in AER with any protein in any group
Nakamura et al[124]	Single meal intervention study (crossover)	Healthy and T2D subjects	10 healthy subjects and 6 T2D subjects	0.7 g/kg soy protein (as bean curd)	0.7 g/kg tuna fish protein or egg white protein or dairy protein (cheese)	Meals fed on separate days	eGFR was only significantly increased after ingestion of tuna fish protein (P < 0.001) and not after consumption of soy, egg white or dairy proteins
Orita et al[125]	Single meal intervention study (crossover)	Healthy subjects	6 male subjects	86.9 g soy protein	86.9 g beef protein or fasting (0 g protein)	Meals fed 1 wk apart	Inulin clearance (GFR) was significantly increased over baseline at 2 h post beef or soy protein compared to fasting (P < 0.005 and P < 0.05, respectively)	First study to show an increase in GFR after a soy protein load in healthy subjects
							Creatinine clearance (GFR) was significantly increased by both beef and soy proteins at 2 and 3 h post-ingestion compared to fasting (P < 0.01)
							Plasma glucagon was significantly increased at 1 to 3 h post-ingestion by both beef and soy protein compared to fasting (P < 0.01)

AER: Albumin excretion rate; BW: Body weight; Ca: Calcium; CrCl: Creatinine clearance; ERPF: Effective renal plasma flow; eGFR: Estimated glomerular filtration rate; F: Female; GFR: Glomerular filtration rate; M: Male; MGP: Membranous glomerulopathy; NS: Nephrosclerosis; P: Phosphorus; PKD: Polycystic kidney disease; PM: Postmenopausal; PTH: Parathyroid hormone; T1D: Type 1 diabetes; T2D: Type 2 diabetes; UAp: Urinary urea appearance rate.