Protein Intake in CKD: The Everlasting Dilemma

To recommend or not to recommend? This is the question that many clinicians ask themselves when considering low protein diets for people living with chronic kidney disease (CKD). Historically, reducing protein intake was the only tool to reduce the production of uremic toxins, which could alleviate symptoms of kidney failure. A low protein diet may indeed help in controlling several metabolic derangements due to uremia; decreasing phosphate intake; reducing acidosis; helping to manage bone disease; and decreasing inflammation, protein carbamylation, endothelial dysfunction, and cardiovascular damage. Conversely, a high protein diet increases the glomerular filtration rate, and, over time, in a diseased kidney, glomerular hyperfiltration may induce further damage on the remnant nephrons (1).

The literature lists several low protein diet options, conventionally divided into “moderately restricted” (i.e., with a protein intake of 0.6 g/kg per day). These include traditional diets, based on the quantity and on the distribution of food; vegan-vegetarian or plant-based, plant-dominant diets; and very low protein (0.3–0.4 g/kg per day) diets, using protein-free foods and mixtures of essential amino acids and ketoacids (2). However, because most Western diets have a higher protein content compared with the recommended daily allowances of 0.8 g/kg per day for the general population, as recommended by the World Health Organization and other organizations, normalization of dietary protein intake should usually be a first step, and sometimes the best option, to reduce protein intake against a high background (3).

Furthermore, the quantity of proteins is not everything. The focus is progressively shifting from quantity to quality of proteins. A diet supplying higher vegetable content and minimally processed foods offers several health benefits, including, in the overall population, a decrease in the incidence of renal dysfunction and, in patients with CKD, possibly a lower progression of kidney function impairment (4, 5).

The Modification of Diet in Renal Disease study (6) was a turning point in the implementation of low protein diets. This large randomized clinical trial showed no benefit from dietary protein restriction in the primary analysis but suggested an advantage in the per-protocol analysis, thus highlighting the importance of compliance or adherence to low protein intake (6). Later, further randomized controlled trials have shown beneficial effects of restricted protein intake, so that the Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines on kidney nutrition strongly recommended, in patients with CKD who are nondiabetic, protein restriction (0.3–0.6 g/kg per day) for CKD stages 3–5 with a high grade of evidence (7) (Figure). Conversely, the recent Kidney Disease: Improving Global Outcomes (KDIGO) guidelines about CKD management suggest normalization of protein intake (0.8 g/kg per day) but leave the door open for further restriction in selected cases (8).

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The protein intake balance in people living with CKD

Citation: Kidney News 16, 6

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Randomized trials are probably not the best way to convince clinical nephrologists of the benefits of different diets because the selected populations enrolled usually differ from those encountered in their daily practice. Adherence may be difficult, and there is still fear of promoting malnutrition or protein energy wasting by restricting protein intake.

We are the offspring of the so-called “nutrition transition,” leading to low consumption of natural, homemade meals and low intake of fruits, vegetables, legumes, beans, nuts, and whole grains. In this context, helping patients achieve a healthy diet, rich in plant-based sources and limited in ultraprocessed food, is probably the first step to undertake. Thus, the new challenge on protein intake in patients with CKD should probably start from selecting better-quality protein sources and high-fiber meals and teaching healthy cooking to achieve a better quality of diet (9, 10).

Attention to “quality first” should not divert attention from quantity. A low protein diet may slow CKD progression and delay or reduce dialysis needs by stabilizing the metabolic balance with lower drug burden. This should be kept in mind, particularly in the more advanced CKD stages. In any case, it is important to stress that protein selection and restriction are only a part, even if probably the most CKD specific, of the nutritional management in patients with CKD (11).

Precision medicine and nutrition precision focus on personalized approaches for a patient-centered management. These are not just words. Dietary recommendations should be based on individual habits, preferences, needs, and disease characteristics. Furthermore, as we seek sustainable nephrology and nutritional practices, we may also remind ourselves that “what is good for the patient is probably also good for the planet” (12).