Comparative Effects of Low-Carbohydrate High-Protein Versus Low-Fat Diets on the Kidney

Allon N. Friedman; Lorraine G. Ogden; Gary D. Foster; Samuel Klein; Richard Stein; Bernard Miller; James O. Hill; Carrie Brill; Brooke Bailer; Diane R. Rosenbaum; Holly R. Wyatt

doi:10.2215/CJN.11741111

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Figure 1.
Flow diagram of participant recruitment.
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Figure 2.
Trends in creatinine clearance. Bars represent 95% confidence interval for means.
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Figure 3.
Trends in urinary calcium excretion. Bars represent 95% confidence interval for means.

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Table 1.

Baseline characteristics

Characteristic	Low-Fat Diet (n=154)	Low-Carbohydrate Diet (n=153)
Age (yr)	44.9±10.2	46.2±9.2
Men, n (%)	49 (31.8)	50 (32.7)
Race, n (%)
white	117 (76.0)	113 (73.9)
African American	33 (21.4)	36 (23.5)
Asian	2 (1.3)	0 (0)
other	2 (1.3)	4 (2.6)
Weight (kg)	103.7±14.4	103.6±15.5
Body mass index (kg/m²)	36.1±3.5	36.1±3.6
Systolic BP (mmHg)	124.6±15.8	124.3±14.1
Diastolic BP (mmHg)	76.0±9.7	73.9±9.4
Serum creatinine (mg/dl)^a	0.9 (0.8, 1.0)	0.8 (0.7,1.0)
Serum cystatin C (mg/L)^a	0.7 (0.6, 0.8)	0.7 (0.6, 0.8)
Serum electrolytes
sodium (mmol/L)	139±2.3	140±2.5
potassium (mmol/L)	4±0.4	4±0.3
chloride (mmol/L)	105±2.6	105±2.1
bicarbonate (mmol/L)	24±2.6	24±2.4
Urea (mg/L)^a	13 (10, 15)	14 (11, 16)
Urine measurements
total volume (ml)	2012±1079	1940±1159
creatinine (mg/24 hr)^a	1630 (1300, 1980)	1585 (1276, 2085)
calcium (mg/24 hr)^a	207 (110, 278)	187 (117, 278)
albumin (mg/24 hr)^a	7 (6, 14)	9 (6, 15)
24-hr creatinine clearance (ml/min)	133±41.8	135±35.3

Data reported as mean ± SD unless otherwise indicated. There were no significant differences between groups for any of the variables.
↵a Data reported as median (25th, 75th percentiles).

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Table 2.

Estimated change from baseline in dietary study groups

Variable	Low-Carbohydrate Diet			Low-Fat Diet
	Study Month			Study Month
	3	12	24	3	12	24
Participants (n)
serum measurements	136	111	74	140	116	83
urine measurements	111	78	56	109	77	66
Weight (kg)	−9.70^a (−10.40 to −9.00)	−11.20 (−12.50 to −9.90)	−6.60 (−8.20 to −4.90)	−8.40 (−9.10 to −7.50)	−10.50 (−12.60 to −9.20)	−7.80 (−9.60 to −6.10)
Serum creatinine (%)^b	−2.40^c (−4.80 to −0.10)	−3.10 (−5.50 to −0.60)	0.10 (−3.10 to 3.40)	1.90 (−0.40 to 4.20)	−0.42 (−2.90 to 2.10)	−1.64 (−4.10 to 0.90)
Serum cystatin C (%)^b	−9.50^d(−11.10 to −7.80)	−4.80 (−6.80 to −2.90)	−1.00 (−3.40 to 1.50)	−1.10 (−2.80 to 0.60)	−3.20 (−4.90 to −1.60)	−0.90 (−2.80 to 1.00)
Serum sodium (mmol/L)	−0.10 (−0.50 to 0.30)	−0.50 (−1.00 to −0.10)	−0.40 (−1.00 to 0.10)	0.40 (−0.00 to 0.80)	−0.30 (−0.70 to 0.20)	0.20 (−0.20 to 0.70)
Serum potassium (mmol/L)	−0.02 (−0.10 to 0.00)	−0.06 (−0.10 to −0.00)	−0.05 (−0.10 to 0.00)	−0.07 (−0.10 to −0.00)	0.003 (−0.10 to 0.10)	−0.03 (−0.10 to 0.10)
Serum chloride (mmol/L)	−0.40 (−0.90 to −0.00)	0.06 (−0.40 to 0.50)	0.06 (−0.50 to 0.60)	0.08 (−0.30 to 0.50)	0.15 (−0.30 to 0.60)	0.19 (−0.30 to 0.70)
Serum bicarbonate (mmol/L)	−0.50 (−0.90 to −0.10)	0.70 (0.30–1.10)	0.50 (−0.10 to 1.00)	−0.20 (−0.60 to 0.20)	0.60 (0.10–1.10)	0.50 (0.00–1.00)
Serum urea nitrogen (%)^b	13.00^d (8.30–17.90)	14.20^c (9.50–19.20)	9.50^a (3.10–16.30)	−1.20 (−5.00 to 2.70)	4.80 (0.20–9.60)	1.20 (−3.70 to 6.30)
Urinary volume (ml/d)	249.00 (79.00–418.00)	487.00^c (296.00–678 .00)	228.00^a (18.00–438.00)	24.00 (−183.00 to 231.00)	49.00 (−124.00 to 222.00)	−40.00 (−205.00 to 125.00)
Urinary creatinine (%)^b	−3.40 (−9.90 to 3.60)	−0.70 (−6.00 to 4.90)	−2.90 (−8.90 to 3.60)	−7.90 (−13.10 to −2.50)	−8.40 (−14.70 to −1.70)	−5.90 (−12.80 to 1.50)
Creatinine clearance (ml/min)	5.20^c (−3.30 to 13.70)	10.10^c (1.50–18.70)	3.70 (−6.70 to 14.10)	−10.60 (−18.30 to −2.90)	−10.70 (−20.00 to −1.30)	−3.50 (−15.10 to 8.10)
Urinary albumin (%)^b	−5.80 (−20.40 to 11.40)	−7.10 (−24.80 to 14.80)	−21.40 (−35.00 to −5.00)	−11.30 (−26.50 to 7.10)	−22.20 (−38.30 to −1.90)	−23.80 (−38.10 to −6.20)
Urinary calcium (%)^b	20.90^d (7.20–36.40)	26.90^c (11.50–44.50)	7.30 (−7.10 to 23.90)	−11.20 (−21.10 to −0.10)	−6.50 (−19.90 to 9.30)	−9.80 (−22.10 to 4.50)

Estimated using a linear mixed-effects model. Data reported as absolute changes from baseline (estimated mean with 95% confidence interval) unless otherwise indicated.
↵a P<0.05 for difference between the two diets at specified time.
↵b Log-transformed for analysis with back-transformed data reported as percentage change (95% confidence interval).
↵c P<0.01 for difference between the two diets at specified time.
↵d P<0.001 for difference between the two diets at specified time.