Comparative effects of low-carbohydrate high-protein versus low-fat diets on the kidney.
OBJECTIVE
Concerns exist about deleterious renal effects of low-carbohydrate high-protein weight loss diets. This issue was addressed in a secondary analysis of a parallel randomized, controlled long-term trial.


METHODS
Between 2003 and 2007, 307 obese adults without serious medical illnesses at three United States academic centers were randomly assigned to a low-carbohydrate high-protein or a low-fat weight-loss diet for 24 months. Main outcomes included renal filtration (GFR) indices (serum creatinine, cystatin C, creatinine clearance); 24-hour urinary volume; albumin; calcium excretion; and serum solutes at 3, 12, and 24 months.


RESULTS
Compared with the low-fat diet, low-carbohydrate high-protein consumption was associated with minor reductions in serum creatinine (relative difference, -4.2%) and cystatin C (-8.4%) at 3 months and relative increases in creatinine clearance at 3 (15.8 ml/min) and 12 (20.8 ml/min) months; serum urea at 3 (14.4%), 12 (9.0%), and 24 (8.2%) months; and 24-hour urinary volume at 12 (438 ml) and 24 (268 ml) months. Urinary calcium excretion increased at 3 (36.1%) and 12 (35.7%) months without changes in bone density or clinical presentations of new kidney stones.


CONCLUSIONS
In healthy obese individuals, a low-carbohydrate high-protein weight-loss diet over 2 years was not associated with noticeably harmful effects on GFR, albuminuria, or fluid and electrolyte balance compared with a low-fat diet. Further follow-up is needed to determine even longer-term effects on kidney function.
Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA. allfried@iupui.edu
Allon N
AN
Friedman
Lorraine G
LG
Ogden
Gary D
GD
Foster
Samuel
S
Klein
Richard
R
Stein
Bernard
B
Miller
James O
JO
Hill
Carrie
C
Brill
Brooke
B
Bailer
Diane R
DR
Rosenbaum
Holly R
HR
Wyatt
D000328:Adult; D050528:Diet, Carbohydrate-Restricted; D018752:Diet, Fat-Restricted; D004044:Dietary Proteins / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D007668:Kidney / Q000502:physiology*; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000178:diet therapy*
D004044:Dietary Proteins