Dietary management of pediatric patients with kidney disease: recommendations by The Korean Society of Pediatric Nephrology and The Korean Society of Clinical Nutrition

Dietary alternatives for insufficient caloric intake

When eating regular meals proves difficult, alternative foods with equivalent calories (kcal) can be selected as substitutes (Fig. 1) [4,5]. To increase the energy intake, jam can be added to bread or crackers, while honey or rice syrup can be added to rice cakes. Even with the same ingredients, energy intake can be enhanced by stir-frying or deep-frying them or making them into pancakes. Additionally, adding sesame oil or perilla oil during the preparation of porridges or side dishes, as well as using olive oil or oriental dressing on salads, can also help boost energy intake.

Figure 1.

Examples of foods with 100 kcal.

Enteral formulas

In patients with kidney disease who require restrictions on protein, potassium, and phosphorus, a specialized enteral formula can be utilized. For infants, increasing the infant formula concentration by reducing the amount of water added can be used to increase its energy content; however, this method may also increase the protein, sodium, potassium, and phosphorus levels in the formula. Therefore, infant formula concentration should not be altered arbitrarily. Instead, energy modules, such as glucose polymers or fat emulsions specifically designed for caloric and nutritional supplementation, can be added to the formula [1–3]. For instance, infants fed formula eight times per day at 100 mL per feeding have a total daily energy of approximately 560 kcal. By supplementing each 100 mL of formula with 3 g of an energy-dense additive (e.g., high-calorie powder), the total energy intake can be increased to approximately 650 to 700 kcal per day, representing a 15% to 20% increase in caloric density [4].

Dietary sources of protein (Table 1)

Table 1.

Major dietary protein sources according to exchange unit [5]

Proteins can be classified into animal-based and plant-based sources [4]. Animal-based protein sources mainly include meats, fish, shellfish, eggs, and milk. Except for milk, animal-derived foods typically contain 8 g of protein per food exchange unit (a standardized measurement system that allows for interchanging foods within the same food group while ensuring equivalent nutritional value). Plant-based proteins include grains, vegetables, legumes (e.g., tofu), and soy milk. Among the sources of plant proteins, legumes have the highest protein content, providing 8 g per exchange unit [5]. Grains and vegetables each provide approximately 2 g of protein per exchange unit, whereas soy milk contains 6 g of protein per exchange unit, which is equivalent to cow’s milk [5].

Protein intake in pediatric patients with nephrotic syndrome

Guidelines recommend that pediatric patients with nephrotic syndrome maintain a protein intake similar to that for healthy children of the same age, without increasing or restricting protein intake even during steroid treatment or proteinuria (Table 2) [6,7]. Historically, high-protein diets had been found to compensate for protein losses in nephrotic syndrome; however, such diets did not improve serum albumin levels and instead accelerated renal damage due to protein overload. Conversely, studies involving low-protein diets in patients with CKD demonstrated that such a diet slowed the decline in renal function but promoted nutritional deficiencies due to inadequate protein intake [8–11]. According to the 2021 KDIGO (Kidney Disease: Improving Global Outcomes) guidelines, protein restriction is recommended for patients with decreased kidney function and proteinuria, although its safety has not been conclusively established in pediatric populations due to concerns about the risk of malnutrition [12]. An exception to this recommendation, however, is patients with congenital nephrotic syndrome who may benefit from high-calorie, high-protein diets.

Table 2.

Recommended protein intake for healthy children and pediatric patients with nephrotic syndrome [6,7]

Protein intake in pediatric patients with chronic kidney disease

To ensure normal growth and adequate nutritional status of pediatric patients with CKD, their protein intake should be carefully planned. Given that strict restriction of protein intake does not necessarily improve preservation of kidney function, guidelines recommend that pediatric patients with CKD consume the same amount of protein as their healthy peers (Supplementary Table 2, available online). However, healthy children and adolescents typically consume more than twice the recommended protein intake. Therefore, CKD patients need to strictly adhere to nutritional guidelines rather than trying to match the high-protein consumption of their peers.

Restricting protein intake often inadvertently reduces the overall caloric and nutrient consumption. Thus, significant protein restriction is not generally recommended for patients with stage 1 to 2 CKD. For those with CKD stage 3 or higher, guidelines recommended a protein intake that closely aligns with age-specific nutritional requirements (Table 3) [1,2,6,7,13].

Table 3.

Recommended protein intake for pediatric patients with CKD [6,7]

Suggested daily meat consumption

A serving of meat weighing approximately 40 g, around the size of a ping-pong ball, contains approximately 8 g of protein [4,5]. For example, the daily recommended protein intake for a 10-year-old boy is approximately 50 g. If the daily protein requirement were to be met exclusively through meat, approximately 250 g (approximately six ping-pong ball-sized portions) would be required (Table 1). However, actual meals typically include rice and vegetables alongside meat. Considering that one bowl of rice contains around 6 g of protein, along with vegetable side dishes, a total of around 20 to 25 g of protein can be consumed daily through these foods. Therefore, an additional 3 to 4 ping-pong ball-sized servings of meat would suffice to meet the protein requirement.

Uric acid-containing foods

Fig. 2 lists the dietary sources of uric acid classified according to purine content [4].

Figure 2.

Classification of foods according to purine content (per 100 g) [4]

Factors elevating uric acid levels

Foods containing sodium

Sodium is abundantly present in condiments or seasonings, pickled foods, processed foods, instant foods, and fast foods. Table 4 lists the primary dietary sources of sodium among Koreans. Accordingly, condiments make up a significant proportion of the daily sodium intake, accounting for approximately 46% [20]. Therefore, pediatric and adolescent patients with CKD should make concerted efforts to reduce their consumption of sodium-rich condiments and limit the frequency of dining out and consumption of processed foods.

Table 4.

Ranking of foods according to sodium content [21]

Recommended daily sodium intake for a 7-year-old child

Given that 1 g of salt contains approximately 400 mg of sodium and that the recommended daily sodium intake for a 7-year-old child is 1,900 mg (Supplementary Table 3, available online), such a child is able to safely consume approximately 5 g of salt per day (1,900 mg divided by 400 mg/g). Typically, around 1 to 2 g of salt is consumed naturally through unprocessed foods, allowing an additional 3 to 4 g of salt to be consumed through condiments or seasonings, which equates to roughly 1 g of salt from the condiments per meal. The amount of condiments containing 1 g of salt is illustrated in Fig. 3 [26].

Figure 3.

Amount of condiments containing 1 g of salt (400 mg of sodium) [26].

Spoon used is 1 tablespoon.

Methods for reducing sodium intake when cooking at home

Patients should also avoid salted foods, processed foods, fast foods, dried fish, and chemically enhanced seasonings, which have high-sodium content [26]. Clear soups or rice water soups (Nurungji-guk) are preferable to stew, given their lower sodium content. Vinegar, lemon juice, wasabi, chili powder, pepper, green onions, onions, garlic, ginger, herbs, perilla oil, or sesame oil can be used to enhance flavor while reducing sodium. Additionally, serving sauces for dipping separately rather than seasoning soups and side dishes directly, preparing only one side dish with adequate seasoning while leaving others unseasoned, or using low-sodium condiments can further reduce sodium intake [27,28].

Methods for reducing sodium intake when dining out

Processed foods often contain high amounts of sodium for preservation purposes; therefore, caution should be exercised when consuming bread, snacks, convenience store meals, frozen foods, and instant foods [26]. When eating school meals or dining out, only consume half portions of high-sodium foods, such as braised or pickled dishes and soups. Moreover, individuals can ask the sauce to be served separately and use minimal amounts for dipping. Consumption of pickles, ketchup, cheese, bacon, and processed meats should also be minimized [26–28].

Dietary sources of calcium and phosphorus

Calcium-rich foods include milk, dairy products, anchovies, oysters, dried seaweed, cheese, and tofu. According to the 2018 Korean National Health and Nutrition Examination Survey [29], Koreans consume an average of 128.1 mg of calcium per day through milk and dairy, accounting for 29.4% of the daily calcium intake. Milk and dairy products, including manufactured infant formulas, are especially important calcium sources for infants and children.

Although phosphorus is found in almost all animal and plant foods, it is particularly abundant in protein-rich foods, such as fish, meat, eggs, dairy products, grains, and nuts. The major dietary phosphorus sources among Koreans [29,30] include rice and animal-based foods, such as pork (lean meat), chicken, anchovies, milk, and eggs. For infants and children, milk and dairy products serve as more significant sources of phosphorus than do rice and meat.

Food additives and supplements

Phosphorus can be consumed through natural foods, as well as food additives and supplements in various forms. Food additives have been widely used in food processing; thus, frequent consumption of processed foods increases the intake of food additives [31]. These additives, which are mostly inorganic phosphates, are more readily absorbed than is phosphorus naturally present in foods. Additionally, phosphates are added to various medications (e.g., antacids and antihypertensive drugs) to aid dispersion and absorption [32,33]. Therefore, assessment of phosphorus intake should consider the consumption of carbonated beverages, processed foods, and medications containing inorganic phosphates.

In Korea, 27 types of phosphates, including potassium phosphate, calcium phosphate, and sodium phosphate, have been approved for use as food additives in food production [34]. Phosphates function as acidity regulators, emulsifiers, nutrient enhancers, leavening agents, and preservatives. In Korea, phosphates are most commonly used in bakery products, processed foods, and complex seasonings. Although Koreans primarily consume phosphorus from natural agricultural and animal products [21], the growing trend of processed food consumption among adolescents may increase phosphate intake from food additives.

Calcium and phosphorus intake in pediatric patients with chronic kidney disease

Regular monitoring of calcium and phosphorus intake, including intake from food additives, processed foods, and calcium-containing medications (e.g., calcium-based phosphate binders), is crucial for pediatric patients with CKD. Calcium intake should align with the recommended daily allowance for age (Supplementary Table 4, available online) and should ideally not exceed twice this amount. Phosphorus intake should also adhere to age-specific recommendations (Supplementary Table 5, available online) while still ensuring adequate nutritional intake. However, given the high phosphorus content in dairy products, fish, and meat, strict adherence to the recommended levels can be challenging, often necessitating the use of phosphate binders to manage phosphorus effectively.

Meal planning for phosphorus control

Meal planning should prioritize foods low in phosphorus (Table 5) [4]. Given that phosphorus from animal-based foods is absorbed more efficiently than that from plant-based foods, animal proteins should be evenly distributed across meals rather than consumed excessively at one time [32]. Considering that phosphorus is water-soluble, boiling foods in plenty of water can be used to reduce their phosphorus content [31,35,36]. After boiling, the cooking water is discarded as it contains high levels of phosphorus. Boiling reduces phosphorus content in vegetables, legumes, and meats by approximately 51%, 48%, and 38%, respectively [4]. Boiling food for over 30 minutes using a pressure cooker is more effective than using a regular pot. If processed foods are desired, they should be cut into small pieces, boiled, and then drained before consumption. Always check the labels on processed foods to identify phosphorus additives (e.g., phosphate compounds) and manage intake carefully.

Table 5.

Foods rich in phosphorus [4]

Calcium-rich beverages as alternatives to milk

Breastfeeding is primarily recommended even for infants with CKD [35]. However, if breastfeeding is not possible and manufactured infant formulas are selected, studies recommend using standard formulas suitable for the infant’s age and weight. As infant formulas advance in stages, their protein and mineral contents increase slightly despite having similar caloric content. Thus, if an infant consumes adequate amounts of formula, maintaining a lower-stage formula might be beneficial to prevent excessive intake of proteins and minerals [4]. Specifically, infants older than 6 months who primarily rely on formula due to difficulties transitioning to complementary foods may consume excessive amounts of minerals when consuming large amounts of advanced-stage formula. The use of formulas low in phosphorus can be considered after consultation with healthcare providers. Table 6 compares the nutritional contents of breast milk and infant formulas [37].

Table 6.

Nutritional contents of breast milk and infant formulas [37]

Dietary sources of potassium and food additives

Table 7 lists dietary sources of potassium. Additionally, potassium intake can be influenced by potassium salts used as food additives in various processed foods. Thus, individuals needing potassium-restricted diets should carefully check the food ingredient label for potassium additives. In Korea, potassium salts approved for use as food additives [34] have been primarily used as acidity regulators, flavor enhancers, nutrient enhancers, coloring agents, sweeteners, emulsifiers, thickeners, stabilizers, flour treatment agents, bleaching agents, preservatives, and leavening agents. Consuming a higher proportion of processed or instant foods can increase potassium intake compared to consuming fresh foods. Patients with hyperkalemia should therefore evaluate nondietary factors causing potassium imbalance (e.g., adjustments to dialysis prescriptions, medication review) before modifying dietary intake.

Meal planning for hyperkalemia management

When consuming a regular diet, processed foods containing potassium additives should be avoided. If hyperkalemia persists, the intake of high-potassium foods should be reduced, and cooking methods that lower the potassium content should be adopted [4]. If dietary adjustments fail to control potassium levels, oral potassium binders may be necessary [38].

Regarding vegetable intake, not all raw vegetables must be blanched. Instead, select low-potassium options and avoid high-potassium varieties. Vegetables can be peeled, removed of their stems, sliced thinly or diced, and then soaked in water (10 times the volume of the vegetables) for at least 2 hours before rinsing and cooking [4,38]. Blanch vegetables in water five times their volume, boil thoroughly, and rinse afterward [4,38].

When consuming fruits, the skin should be peeled off before eating. Be cautious with dried fruits, which typically have at least twice the potassium content of fresh fruits [4]. Canned fruits generally have lower potassium content and can be consumed safely in moderation, but excessive syrup intake should be limited [4].