Calcium
Calcium is necessary for bone mineralization and to prevent fractures [
56]; therefore, a low dietary calcium intake is of concern. Conversely, a high calcium intake may lead to vascular calcification, progressive vessel stiffness and left ventricular failure [
57‐
61]. Calcium intake in the infant is unlikely to be excessive or deficient if nutritional requirements are met from breastmilk, IF, and some contribution from solid foods. Calcium intake should provide at least 100% of the SDI (Table
7) but be no more than twice the SDI. In special circumstances, such as for infants with mineral-depleted bone, a higher calcium intake of > 200% SDI may be needed to replenish bone calcium stores and is likely to require calcium supplementation in addition to dietary calcium. In the case of persistent hypocalcemia or a high parathyroid hormone level, calcium intake should be increased above 200% SDI for a short period under close medical supervision [
54]. Additional calcium can be provided through calcium supplementation and high calcium dialysate. The use of calcium-rich foods, such as dairy products (cheese, yogurt, fromage frais) which infants are most willing to eat, may need to be limited as these will also increase dietary phosphate intake. Absorption of calcium requires adequate vitamin D and often requires supplementation (usually both native and active forms) [
30,
31]. It should be noted that frequent vomiting may lead to metabolic alkalosis, which in turn might affect the interpretation of serum calcium levels—ionized calcium levels must be measured so that hypocalcemia can be detected and managed appropriately.
Table 7
Suggested dietary intake (SDI) for calcium and phosphate
0 to < 4 months | 220 | 120 |
4 to < 12 months | 330–540 | 275–420 |
In the case of persistent mild to moderate hypercalcemia, management is mainly medical: reducing or stopping calcium supplements, calcium-based phosphate binders, and native and active vitamin D, and using lower calcium dialysate. A temporary reduction of dietary calcium may also be necessary. If hypercalcemia is severe and persists, a nutritionally complete specialized low calcium formula may fully or partially replace IF or breastmilk (mothers should be supported to express and safely store their breastmilk until it can be fed to their infant). In addition to dairy products, other calcium-rich foods may need to be restricted: green-leafy vegetables, beans, ground nuts and nut butters, and calcium-fortified foods. Using deionized or distilled water to reconstitute formula also reduces calcium intake. Regular assessment of dietary calcium is required, especially when calcium intake is reduced below the SDI.
Phosphate
Table
7 shows the SDI for phosphate. Serum phosphate is likely to be within the normal range if the infant is fed breastmilk or whey-dominant IF. However, phosphate retention begins early in the course of CKD, and if there is either persistent hyperphosphatemia or persistent hyperparathyroidism in the presence of normal calcium levels, dietary phosphate should not exceed the SDI for young infants, and intake should be reduced to the lower end of the SDI range for infants older than 6 months [
54]. The introduction of complementary solid foods that are easy to swallow, particularly soft dairy foods and eggs, increases phosphate intake. Whole grain cereals, although higher in phosphate than refined varieties, need not be restricted as the inclusion of fiber in the diet is beneficial. Foods with a suitably lower phosphate content are shown in Table
8. Processed foods containing phosphate additives should be avoided as they are a source of highly bioavailable inorganic phosphate, which is almost completely absorbed [
62].
Table 8
Controlling phosphate and potassium intakes
Continue beyond 1 year | Breastmilk, whey-dominant infant formula | Milk | Breastmilk, whey-dominant infant formula | Continue beyond 1 year |
Portion size may need to be controlled | Cottage, cream, ricotta cheese; paneer | Cheese, yogurt | Any type | Portion size may need to be controlled |
| Baby cereals; rice, pasta, noodles, couscous, millet, bulgur wheat, semolina, tapioca; bread, chapattis; potatoes | Starchy foods | Baby cereals; rice, pasta, noodles, couscous, millet, bulgur wheat, semolina, tapioca; bread, chapattis High K: potatoes—cut into small pieces and double boil, discard cooking water | |
Portion size may need to be controlled | Fresh, unprocessed, any type | Meat, chicken, fish | Fresh, unprocessed, any type | Portion size may need to be controlled |
| Egg white | Eggs | Whole egg | |
| Any type, e.g., lentils, split peas, chickpeas; black eye, broad, butter, cannellini, red kidney beans; tofu; houmous | Pulses, legumes | Lentils, split peas, chickpeas; cannellini, red kidney beans; tofu; houmous High K: black eye, broad, butter beans | Portion size may need to be controlled |
Portion size may need to be controlled | Any type, e.g., almonds, hazelnuts, peanuts, walnuts; pumpkin, sesame, sunflower seeds; tahini paste | Nuts and seeds (ground, pastes, butters) | Almonds, hazelnuts, peanuts, walnuts; sesame and sunflower seeds; tahini paste High K: pumpkin seeds | Portion size may need to be controlled |
| Any type, e.g., avocado, broccoli, brussels sprouts, butternut squash, cabbage, carrot, cauliflower, courgette, okra, plantain, pumpkin, swede, sweet potato, tomato, yam | Vegetables | Broccoli, butternut squash, cabbage, carrot, cauliflower, courgette, pumpkin, swede High K: avocado, brussels sprouts, okra, plantain, sweet potato, tomato, yam | Portion size may need to be controlled |
| Any type, e.g., apple, apricot, banana, blueberries, lychees, mango, melon, orange, papaya, pear, pineapple, raspberries, strawberries | Fruit | Apple, blueberries, lychees, pear, pineapple, raspberries High K: apricot, banana, mango, melon, orange, papaya, strawberries | Portion size may need to be controlled |
Avoid | Phosphate additives—bioavailability up to 100% | Food additives | Potassium additives—bioavailability 90–100% | Avoid |
Although breastmilk and whey-dominant IF are naturally low in phosphate (15 mg/100 mL and average 30 mg/100 mL, respectively), a specialized renal-specific low potassium infant formula, that also has a lower phosphate content, may be given so that dietary restrictions can be liberalized, allowing a greater variety of food choices, which may encourage more normal development and behaviors around food. Table
9 shows the composition of a typical renal-specific formula and how to adapt a whey-based IF to reduce phosphate content. Diluting the IF needs to be done with extreme caution as this also reduces the energy, protein, vitamin, and mineral content of the formula. Energy and protein modules must be added, together with a suitable vitamin and mineral preparation, to restore the full composition and maintain nutritional adequacy.
Table 9
Specialized and adapted infant formulas per 100 mL
Typical whey-dominant infant formula |
3 scoops powder (13 g) per 100 mL | 66 | 1.3 | 7.2 | 3.6 | 17 | 68 | 51 | 25 |
Typical low calcium infant formula |
13 g powder per 100 mL | 66 | 1.9 | 7.0 | 3.4 | 29 | 84 | < 7 | 46 |
Typical renal-specific low potassium infant formula |
13 g powder per 100 mL | 65 | 1.0 | 8.2 | 3.1 | 31 | 14 | 16 | 12 |
Diluted whey-dominant infant formula providing less calcium, phosphate and potassium |
2 scoops powder (9 g) | 47 | 0.9 | 5.0 | 2.5 | 12 | 47 | 35 | 17 |
0.5 g protein powder | 2 | 0.5 | 0 | 0 | 0* | 0* | 0* | 0* |
2.5 mL fat emulsion | 11 | 0 | 0 | 1.3 | 0 | 0 | 7 | 0 |
2 g glucose polymer | 8 | 0 | 2.0 | 0 | 0 | 0 | 0 | 0 |
Per 100 mL | 68 | 1.4 | 7.0 | 3.8 | 12 | 47 | 42 | 17 |
Renal-specific low potassium infant formulas should not be used as the sole source of nutrition as their low potassium content may cause a precipitous fall in serum potassium. Finally, phosphate binders may be required with more advanced CKD and the development of hyperphosphatemia (added to bottle feeds and moist foods), as any dietary restriction may have a negative impact on an existing reluctance to eat and further decrease intake of solids.
In the case of hypophosphatemia, dietary phosphate should be increased so as to achieve age-appropriate serum phosphate levels. The easiest way to do this is to offer more milk- and egg-based foods; phosphate supplements may be necessary if this approach is not tolerated or does not correct the hypophosphatemia.
Potassium
Infants are at risk for developing hyperkalemia in association with moderate to severe CKD. Whereas a reduced potassium intake is usually indicated, hyperkalemia can result from catabolism when there is deficient energy intake [
9]. This can be resolved by the addition of energy modules to the infant’s usual formula or EBM (Table
5). There are no data to suggest potassium requirements for children with CKD. Extrapolating from adult data, KDOQI recommends an initial target potassium intake of 1–3 mmol/kg/day for infants to maintain a normal serum concentration [
25]; however, the PRNT recommends that dietary potassium intake is only adjusted if the serum potassium level is outside the normal range: 3.5–5.0 mmol/L in infants, and 3.5–5.5 mmol/L in neonates, based on serial measurements [
55].
Before adjusting the diet, the many non-dietary causes of hyperkalemia, such as pseudohyperkalemia, medications that affect serum potassium (e.g., some laxatives, angiotensin-converting enzyme inhibitors, renin–angiotensin–aldosterone system inhibitors, and beta-blockers), metabolic acidosis, constipation, and the dialysis prescription, should be addressed [
55]. Severe, life-threatening hyperkalemia requires rapid medical intervention with discontinuation of all sources of potassium from medications, parenteral fluids, formulas, and food.
Serum potassium is likely to be within the normal range in the infant with mild to moderate CKD if fed breastmilk or whey-dominant IF. However, if there are persistent episodes of hyperkalemia, reduced intake of potassium can be achieved by gradually replacing some of the breastmilk or IF with a specialized renal-specific low potassium IF (Table
9). Serum potassium levels need to be regularly checked to ensure they are maintained in the normal range. Attention also needs to be paid to the changes in nutrient profile, as there is often decreased calcium and phosphate content and, for some products, an increased sodium content due to the renal-specific formula. If a renal-specific low potassium IF is not available, a whey-based IF can be adapted to reduce its potassium content (Table
9). As described above, diluting an IF needs to be done with great caution as this also reduces the energy, protein, vitamin, and mineral content. If EBM is diluted, it too must have nutritional adequacy restored by the addition of energy and protein modules and an appropriate vitamin and mineral supplement given. There is no evidence that reducing maternal dietary potassium has any impact on the potassium content of breastmilk. Generally, a renal-specific low potassium IF should only be used as the sole source of nutrition in the short term (hours rather than days) as the low potassium content may cause a rapid fall in serum potassium. If used solely in the initial treatment of moderate to severe hyperkalemia, whey-dominant IF or breastmilk should be introduced as soon as serum potassium levels allow. Some infants may benefit from the extended use of a renal-specific formula; however, caution is advised as in addition to a decreased potassium intake, there will be decreased calcium and phosphate intakes and, with some formulas, an increased sodium intake. An adult renal-specific low potassium formula can also be used in infants to reduce serum potassium [
63], but the nutritional profile needs to be carefully checked for its suitability.
An alternative therapeutic approach to address hyperkalemia is with the use of a potassium-binding resin (sodium polystyrene sulfonate or calcium polystyrene sulfonate). The resin is added to the liquid feed with active mixing, followed by at least 30 min for the resin to settle, and decanting the liquid feed once the gel has formed. Studies have shown a variable reduction in serum potassium levels in infants fed breastmilk and IF using this approach, but there are also other effects: an increase in serum iron, sodium, sulfur, and pH and a decrease in calcium, copper, manganese, phosphate, and zinc [
64‐
72]. Pre-treatment of IF with these resins has also resulted in hypokalemia, hypernatremia, and hypocalcemia [
64]. It is advisable to monitor electrolytes and micronutrients that may be altered by these potassium binders, but they are rarely used for long-term management as they carry a high risk of causing severe constipation and even bowel necrosis. More recently, pre-treatment with patiromer (a calcium-based cation exchange polymer) has been found to decrease the potassium content of IF, with an increase in calcium, magnesium, sodium, and phosphate [
73].
Dietary potassium intake increases with the introduction of solid foods, the first foods often being vegetables, potatoes, and fruits, which have a high potassium content that may potentially aggravate hyperkalemia. The routine omission of vegetables and fruits from the diet based simply on their potassium content should be discouraged, considering that the bioavailability of potassium in unprocessed plant foods is no more than 60% [
74]. These foods also offer other nutritional benefits such as vitamins, minerals, and fiber. For adults, Kidney Disease Improving Global Outcomes (KDIGO) suggests an overall healthy dietary pattern promoting low potassium plant-based foods, especially vegetables [
75]. It has also been suggested that it may be beneficial to choose foods with a low potassium to fiber ratio to enable a higher fiber intake to be maintained while lowering dietary potassium [
76]. There is no reason why infants should not benefit from a diet rich in fruits, vegetables, and whole grains.
Fruits and vegetables with a lower potassium content can be offered (Table
8), along with advice on portion size of other high nutritional value foods with a high potassium content: meat, poultry, fish, eggs, pulses (peas, beans, lentils) and cereals (grains). The potassium content of refined cereals is lower than whole grain varieties, but the bioavailability of potassium may be higher; they are also lower in other essential nutrients and fiber, so they may not be the preferred choice. Families may find it helpful to have lists of foods with low, moderate, and high potassium content with a daily allowance of each category. However, it is not usually necessary to offer this as the infant’s appetite is generally low and the small amounts of foods taken are of no concern.
Cooking methods can reduce the high potassium content of potatoes and other tuberous roots and legumes; cooking in ample water reduces potassium content by 35–80% while soaking raw food has very little effect [
70,
77‐
88]. Cutting potatoes into small pieces and then double-cooking (bringing the water to a boil and then replacing it with fresh water) reduces the potassium content further [
81,
82]. Microwave cooking reduces the potassium content of foods, but to a lesser extent than boiling [
87]. Sous-vide cooking [
89] and frying [
85] increase potassium content of foods. Caregivers should be advised about these cooking methods by a dietitian, as boiling also reduces the amounts of other minerals and water-soluble vitamins.
Once the infant is taking a mixed diet, the use of renal-specific low potassium IF instead of whey-dominant IF allows for the inclusion and greater variety of high potassium foods. Processed foods containing potassium additives should be avoided as they provide an unnecessary source of potassium with high (90–100%) bioavailability [
90,
91].
In the case of hypokalemia, the initial approach is to address any medical causes, such as excessive dialysate potassium losses, medications (potassium binding resins, diuretics), gastrointestinal losses (vomiting, diarrhea), or metabolic alkalosis. Severe, life-threatening hypokalemia requires prompt medical intervention, usually with intravenous potassium infusion. If there is persistent hypokalemia, dietary potassium intake should be increased by including higher potassium-containing foods. If a low potassium IF formula is being used, this should be changed to a whey-dominant IF in a stepwise fashion.