While most of us are aware of calcium and its vital role in our bone health, fewer perhaps are aware that phosphate also plays an equally important role.
Phosphate is an essential mineral which has multiple roles in the human body. It’s involved in the production of energy and plays a role in the normal function of our nerves and muscles. It maintains blood pH and forms a key part of our bones and teeth. In fact, 85% of all phosphate is found in our bones, and together with calcium, it forms a strong framework to give bones structure and strength.
Just as it is with calcium, the phosphate content of our body is regulated. When we need more, the gut is signalled to increase absorption, the kidneys will excrete less, and our bones can release more. Also like calcium, this regulation is in part the job of parathyroid hormone. If the phosphate level of the blood becomes too high, parathyroid hormone acts on the kidneys to cause more to be excreted.
In hypoparathyroidism, when parathyroid hormone levels are low or non-existent, the kidneys lose their signal to excrete phosphate in the urine and blood levels can rise. Prolonged high phosphate levels (hyperphosphataemia) can lead to calcifications in the kidneys, reducing their function and resulting in kidney disease.
Sources of phosphate
Phosphate is an abundant mineral found in most foods. It occurs in particularly high amounts in dairy products, meats, and vegetables.
The phosphate found naturally in foods is called organic phosphate. In meat and dairy products, the organic phosphate is in a soluble form and so has a high bioavailability, approximately 60-70% of what we eat is absorbed. While the variety found in plant foods is insoluble and has a much lower bioavailability, typically less than 50%. In plants, phosphates are bound to phytates, and since we lack the enzyme phytase which is necessary to break the bond between phosphate and phytate, less phosphate is absorbed in our small intestine and is instead excreted in our faeces.
Phosphates can also exist in an in-organic form, and these are the variety which are frequently added to foods as additives and preservatives. These phosphates are highly bioavailable with almost 100% being absorbed in the small intestine. Phosphate is usually added to fast foods, ready to eat meals, canned and bottled drinks, preserved meats and most other processed foods.
How much phosphate should we be consuming?
In the UK the adult daily requirement for phosphate is 550mg/day, however our daily consumption far exceeds this at approximately 1300mg/day, more than twice the recommended daily allowance. Unfortunately, guidelines on phosphate consumption specifically for hypoparathyroidism are vague, ranging from no specific advice to simply suggesting a lower intake. Since phosphate is such an abundant mineral, avoiding it all together is very difficult and usually unnecessary.
Unless you have been advised by your health professional to significantly lower your phosphate intake, the general recommendation in hypoparathyroidism is to be aware of the phosphate content of your diet and aim to reduce your intake where possible.
Much of the phosphate found in our diet comes from added phosphates. Up to 50% of our daily phosphate intake is estimated to come from the consumption of processed foods, fast foods and take-aways. The simplest way to reduce our phosphate intake is therefore, to cut back on foods to which phosphates have been added. As previously mentioned, this variety of phosphate is easily absorbed and can readily elevate blood phosphate levels. Checking the ingredient labels of processed foods and drinks can help you identify if they contain any phosphate additives.
It is important to be aware that some nutritional supplements also contain added phosphate. Dicalcium phosphate (E341) for example, is frequently used in the manufacturing of tablets as a flow agent, it stops powdered products from lumping together during processing. Some of the supplements that we use in the treatment of hypoparathyroidism, such as magnesium and Vitamin D, can contain added phosphate and so it is important to check labels and where possible, purchase products with no added phosphate.
The following table gives examples of the types of phosphates which may be added to foods and examples of the foods they might be found in.
Table 1. Phosphate additives and where to find them:
| E number | Additive name | Food examples |
| E338 | Phosphoric acid | Beer, processed meats eg. sausages, sweets, cakes, chocolates, Cola and other fizzy drinks, jams, vegetable fats and oils |
| E339 | Sodium phosphates (mono, di and tri) | Frozen seafood and processed meat eg. ham, hot dogs and salami |
| E340 | Potassium phosphates (mono, di and tri) | Frozen meals eg. fish fingers, canned foods eg. soup and vegetables |
| E341 | Calcium phosphates (mono, di and tri) | Self-raising flour, cake and pancake mixes, powdered milk drinks e.g hot chocolate, instant pasta/noodles, microwave rice and sauces |
| E343 | Magnesium phosphate (mono and di) | Salt substitute, prepared mustard |
| E442 | Ammonium phosphate | Baked goods, puddings, baking powder, frozen desserts, margarine, whipped toppings and yeast foods |
| E450 | Di-phosphates | Cakes, instant mashed potatoes and cheese |
| E451 | Tri-phosphates | Fish fingers, cheese spread |
| E452 | Poly-phosphates | Dried foods and desserts, cheese spread |
| E1410 | Monostarch phosphate | Ice cream, pizza, battered fish, salad dressings |
| E1412 | Distarch phosphate | Bread, cereal bars, breakfast cereals |
| E1413 | Phosphated distarch phosphate | Cheeses |
| E1414 | Acetylated distarch phosphate | Gravies and sauces |
Ref: FAO/WHO Food Standards, 2023
For those with hypoparathyroidism, being aware and reducing where possible, our intake of high phosphate foods can also be useful. Foods such as meat, fish, pulses, nuts, and dairy foods all contain phosphate, however these are also important sources of protein and other nutrients and so should not be eliminated but either reduced or substituted for lower phosphate alternatives.
The following table lists some very high phosphate foods and lower phosphate alternatives.
Table 2. Very high phosphate foods
| Food category | High phosphate | Lower phosphate alternative |
| Breads and cereals | All bran, branflakes, museli, instant oats Wholemeal bread | Cornflakes, Weetabix and whole oat porridge English muffins, croissant and bagels White bread, flat breads, tortillas, pita bread and sourdough bread
|
| Puddings | Instant milk desserts and coconut milk desserts Ice cream | Fruit with cream Fromage frais (120g) |
| Meat | Organ meats eg. liver, heart, brain Game meats Pre-cooked packaged ham and deli meats Highly processed meats eg. hot dogs, bacon and sausage | Fresh chicken, turkey, beef, lamb, pork, veal, homemade burger patties and meatballs |
| Fish | Shellfish, crab, oysters Oily fish with edible bones eg. sardines, pilchards and whitebait | Plain fresh fish eg. haddock, cod, salmon, trout. Tinned fish eg. salmon and tuna |
| Dairy products | Processed cheese eg. triangles, slices and spreads Milk Evaporated and condensed milk Custard Yoghurt | Hard cheese (limit to 30g/day) Cream cheese, cottage cheese and ricotta Rice milk and almond milk Milk – limited to 300mls/day |
| Beverages | Beer/ale Cocoa, milk-based drinks, chocolate drinks and malted milk drinks Carbonated drinks especially dark colas | Coffee, tea, juice, lemonade, fizzy orange drinks, ginger beer, sparkling water |
| Other foods | Chocolate and cocoa and foods containing them eg. cake, muffins, biscuits, toffee and fudge Marmite and bovril Cake mixes Nuts and foods containing them eg. muesli, cereal bars, peanut butter, satay sauces. Seeds Oven baked chips Eggs Hummus | Homemade cakes, shortbread, plain biscuits Fruit, rice cakes, unsalted pretzels and unsalted popcorn, Jam and honey Bread sticks, wheat based crisps and crackers Home-made potato chips |
Ref: National Kidney Foundation, 2022 and Oxford University Hospitals NHS Foundation Trust, 2019
General guidance
In addition to reducing our overall intake of added phosphates and high phosphate foods, there is some specific advice with regards to dairy foods and meat when it comes to kidney health.
Dairy
Dairy foods are excellent sources of calcium, however, they are also very high in phosphate. While there is currently no specific dairy allowance for persons with hypoparathyroidism, to keep phosphate intake low, it may be advisable to follow the guidelines which are given to those requiring a renal diet due to chronic kidney disease (CKD).
The recommendation for those following a renal diet is that milk and milk products e.g soya milks, yoghurts, fromage frais, ice cream and cheese, are limited to 3 serves per day.
The following table gives examples of a single serving on a renal diet.
Table 3: Dairy serving sizes
| Serving size | Food |
| 100ml | Cows milk (full cream, semi skimmed, skimmed or UHT), Soya milk (fortified) |
| 200ml | Rice, Oat or Soya milk (unfortified) |
| 15g | Hard cheese eg. cheddar, edam, red leicester |
| 7g | Parmesan cheese |
| 30g | Brie, feta, mozzarella, and stilton cheese |
| 60g | Cottage or ricotta cheese |
| 100g | Fromage frais |
| 125g | Soya yoghurt |
| 2 scoops (120g) | Ice cream |
| 75ml | Custard |
| 75g | Yoghurt |
Ref: Royal Devon and Exeter NHs Foundation Trust, 2022
Meat
While meat products provide an excellent source of protein, a diet high in meat can also add a substantial amount of phosphate. Aim to keep your serving sizes between 90-120grams (cooked weight), which equates to around the size of the palm of your hand.
Non-meat sources of protein such as beans, lentils and tofu also contain phosphate, however the phosphate in these plant sources has a much lower bioavailability. To help lower your overall phosphate intake, try substituting animal protein for plant protein several times per week.
On occasions where your meal is particularly meat heavy, a calcium carbonate supplement can act as a phosphate blocker. Taking a supplement with your meal will result in less phosphate being absorbed at that meal, the calcium carbonate will bind with some of the phosphate and then pass through the gut and be excreted via faeces.
By Tania Gelmetti
Jan 2023