Low-Carb Diets Do Not Damage the Kidneys

Low-carbohydrate, high-protein weight loss diets do not cause noticeably harmful effects to patients' kidney function or their fluid and electrolyte balance, according to a new study.

Researchers at the Indiana University School of Medicine (Indianapolis, USA) compared the effects of a low-carbohydrate, high-protein diet in 307 obese individuals without kidney disease between 2003 and 2007. The patients were randomly assigned to a low-carbohydrate high-protein or a low-fat weight-loss diet for 24 months. The main outcomes included renal filtration (GFR) indices (including serum creatinine, cystatin C, creatinine clearance); 24-hour urinary volume; albumin; calcium excretion; and serum solutes at 3, 12, and 24 months.

The results showed that compared with the low-fat diet, low-carbohydrate high-protein consumption was associated with minor reductions in serum creatinine and cystatin C at 3 months, and relative increases in creatinine clearance at 3 and 12 months; serum urea at three 12, and 24 months; and 24-hour urinary volume at 12 and 24 months. Urinary calcium excretion increased at 3 and 12 months, without changes in bone density or clinical presentations of new kidney stones. The study was published ahead of print on May 31, 2012, in the Clinical Journal of the American Society of Nephrology (CJASN).

“In healthy obese individuals, a low-carbohydrate high-protein weight-loss diet over two years was not associated with noticeably harmful effects on GFR, albuminuria, or fluid and electrolyte balance compared with a low-fat diet,” concluded lead author Allon Friedman, MD, and colleagues. “These results are relevant to the millions of healthy obese adults who use dieting as a weight loss strategy.”

Low-carbohydrate, high-protein diets, such as the Atkins diet, Protein Power, The Zone, and others eliminate, or at least severely restrict, refined carbohydrates, such as white bread, white rice, white pasta, most crackers, tonic, sweets, jams and jellies, which all give a sugar jolt. By reducing these types of carbohydrates, the blood sugar and insulin levels can be better controlled. Concerns about low-carbohydrate/high-protein diets are that they are high in protein (making kidney stress more likely, especially for those prone to kidney problems); very low in carbohydrates (causing ketosis and bad breath); high in saturated fat (leading to increased cholesterol and risk of coronary heart disease); and contain less plant proteins, fiber, and fresh fruit (leading to constipation and diminished cancer prevention).

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Indiana University School of Medicine