When I finished medical school in 1986, restricting protein intake in patients with reduced kidney function was still part of standard practice. This practice, has since been long abandoned (having probably done more harm than good), but notions about higher protein intake somehow being harmful to kidneys lingers on.
Thus, I was interested by a recent study by Pedersen and colleagues from the University of Adelaide, Australia, published in Nutrition, Metabolism and Cardiovascular Disease, which examined the effect of of a high-protein calorie restricted diet on overweight individuals with type 2 diabetes, albuminuria and reduced kidney function (estimated GFR of >40 ml/min/1.73m2).
Subjects were randomised to 12 months of a standard-protein diet (protien:fat:carbohydrate ratio 20:30:50 % of energy) and one where energy from carbohydrates was reduced and replaced by protein (30:30:40 % of energy).
Both groups lost a significant amount of weight over 12 months (6.6 Kg on the standard-protein diet, 9.7 Kg on the high-protein diet).
The diets had no impact on kidney function despite improvements in diabetes control.
Of note, only 45 of the 76 volunteers completed the study – a drop-out rate of over 40%
Overall, the study shows that differences in carb to protein ratios matter neither in terms of weight loss nor in their impact on kidney function.
Perhaps, even more importantly, the study shows that trying to keep people on diets – even in clinical trials – is challenging, with almost half the subjects abandoning their diet within 12 months.
As I have noted before, diets only work when you stick with them. Rather than obsessing about the exact composition of your diet, it may be best to chose the one you like best and can actually stay on.