Diet and fluids on dialysis, with tropical food in mind

Two things to know before anything else

First: there is no single kidney diet. The 2020 KDOQI nutrition guideline explicitly moved potassium and phosphorus advice towards individualisation rather than blanket restriction. The right diet depends on your modality, your remaining kidney function, your blood results, your other conditions and what you actually eat. If you have been handed a generic list of banned foods and nothing else, you have been short-changed.

Second, and more important: malnutrition kills more people on dialysis than a high-potassium meal does. Protein-energy wasting is common in dialysis and it is strongly linked to poor outcomes. Restricting food is not automatically the safer choice. A diet so frightening that you stop eating properly is a dangerous diet, whatever it says about bananas.

So the goal here is not fear. It is a small number of levers that actually matter, pulled in the right order, with a renal dietitian who knows your numbers.

Salt: the lever almost nobody is told about first

If you take one thing from this page, take this. The usual advice for fluid overload is "drink less". It is nearly useless advice, because it asks you to fight thirst with willpower, three times a day, forever.

The chain actually works like this:

Salt makes you thirsty. Thirst makes you drink. Drinking makes you gain fluid between sessions. That gain sets how fast the machine has to pull fluid off. And a fast pull is what causes cramps, blood pressure crashes, and hours of feeling wiped out afterwards.

So the most practical fluid advice is not "drink less". It is "eat less salt, and you will want to drink less". NIDDK puts it plainly: too much sodium makes you thirsty, which makes you drink more liquid.

KDOQI recommends less than 2,300 mg of sodium a day (roughly under 5 to 6 g of salt) across the stages of kidney disease. Most of that does not come from the salt cellar. It comes from processed and takeaway food, bread, cured and processed meats, stock cubes, sauces, crisps and salted snacks.

Fluid

We will not give you a number, and you should be wary of any website that does. Your fluid allowance depends on how much urine you still pass, on your treatment, on your dry weight, and on the climate you live in. It belongs to your unit.

What we can tell you is how they tend to think about it. A rule of thumb used by many UK units for people on haemodialysis is roughly 500 mL a day plus however much urine you passed in the last 24 hours. That is a rule of thumb, not a prescription, and allowances differ by unit, by residual function, by dialysis schedule and by climate. Yours may be quite different, and yours is the one that counts.

Two things people consistently get wrong:

• Fluid is not only drinks. Soup, gravy, sauces, ice, jelly, ice cream, yoghurt and juicy fruit all count. NIDDK also names melon, grapes, apples, oranges, tomatoes, lettuce and celery as high-water foods. In a resort, the iced drinks, the sorbet and the fruit platter are exactly the trap.
• Your remaining urine is precious. As it declines, the allowance tightens. It is one of the strongest practical arguments for peritoneal dialysis and for protecting whatever function you have left.

Things units genuinely teach, which help: measure the day's allowance into a jug in the morning and drink only from it, use small cups, suck ice chips (and count them), freeze grapes, use sugar-free gum or hard sweets, rinse your mouth without swallowing, treat a dry mouth properly, take tablets with meals rather than with extra drinks, and keep blood sugar controlled if you are diabetic, because high glucose makes you thirsty.

Protein: the counterintuitive one

This one catches people out badly, and it is worth being clear about, because getting it wrong makes you ill.

Before dialysis, protein is often restricted. Once dialysis starts, it goes up, roughly doubling. Dialysis removes amino acids, and peritoneal dialysis removes protein directly into the dialysis fluid. People who carry their careful pre-dialysis low-protein habits into dialysis become malnourished, and malnutrition is far more dangerous than the phosphate that comes with the protein.

The KDOQI 2020 recommendations, so you can see the shape of it: for people with kidney disease not yet on dialysis, roughly 0.55 to 0.60 g of protein per kg of ideal body weight per day (a little higher with diabetes); for people on maintenance haemodialysis or peritoneal dialysis, roughly 1.0 to 1.2 g per kg per day. Your dietitian works out what that means in food for you. It is not a number to apply to yourself from a website.

Potassium: respect it, but do not let it starve you

Potassium sits in a narrow safe window. Too high can disturb the rhythm of the heart, and NIDDK does not soften it: eating too much potassium can be dangerous to your heart and may even cause death. Too low is also dangerous.

Then come the nuances, and they matter enormously.

• KDOQI 2020 sets no universal milligram limit. It recommends that potassium intake be individualised to keep the level in your blood in range. Most people have been handed a photocopied list. That is not what the guideline says.
• Your modality changes everything. People on haemodialysis, especially across the long weekend gap, are the ones genuinely at risk of a high level. People on peritoneal dialysis often run low, and may be told to eat more potassium, not less.
• The evidence for blanket restriction is weaker than you have been led to believe. Cutting out fruit and vegetables wholesale can damage the diet as a whole, and the evidence that it prevents high-potassium events is thinner than clinicians often assume. That is exactly why the guideline shifted to individualisation.

Foods commonly limited when levels run high on haemodialysis: potatoes, bananas, oranges and orange juice, tomatoes and tomato products, avocado, dried fruit, nuts, beans and pulses, chocolate, coffee in quantity, milk in quantity, and potassium-based salt substitutes. NIDDK advises that people on haemodialysis usually have only about half a cup of milk a day, mainly because of the phosphorus.

Cooking changes the numbers. Boiling vegetables and starchy staples in a large volume of water and throwing the water away leaches potassium out of them. This is standard renal dietetic teaching, and it applies directly to breadfruit and cassava. We are not going to publish a percentage, because we could not verify one for these particular foods, and a made-up number would be worse than none. Ask your dietitian how far to rely on it.

The local food: what is actually on the table in Seychelles

Generic renal diet sheets are written for temperate countries. They warn you about potatoes and bananas and say nothing at all about breadfruit, cassava or coconut, which is not very useful if that is what you eat. The Ministry of Health's 2023 survey found that rice and fish are eaten on most days by many people in Seychelles, often more than once a day.

These are verified values from the USDA food composition database, per 100 g. They are here so that you can have an informed conversation with your dietitian, not so that you can write your own diet.

Local foods that are high in potassium

Local fruit that is lower in potassium

Fish

Fish is excellent protein, and protein is something you need more of on dialysis, not less. NIDDK recommends high-quality protein (meat, poultry, fish, eggs) for people on haemodialysis because it produces less waste for the same nourishment.

But fish is not free of potassium or phosphorus, and it is worth knowing the numbers rather than guessing. Fresh yellowfin tuna, raw, contains about 441 mg of potassium and 278 mg of phosphorus per 100 g. Cooked (by dry heat), the same fish concentrates to about 527 mg of potassium and 333 mg of phosphorus per 100 g, because water has been driven off.

The message is not "avoid fish". It is: fish is a good choice, and portion size still matters. That is a conversation with a dietitian who can look at your blood results, not a rule anyone can write for you here.

Phosphate: where the real win is

High phosphate pulls calcium out of your bones, and phosphate combined with calcium deposits in places it should not, including blood vessels, the heart, the lungs and the eyes. Over years, the National Kidney Foundation is clear, this raises the risk of heart attack and stroke. It also drives the itching that so many people on dialysis describe. Normal serum phosphorus is around 2.5 to 4.5 mg/dL; UK units typically quote a target range of about 0.8 to 1.5 mmol/L for people on dialysis, and local targets vary.

Now the single most useful fact about phosphate, and it is not the one on the leaflet: not all phosphate is equal.

• Phosphate additives are almost completely absorbed. The National Kidney Foundation states it flatly: phosphorus from food additives is completely absorbed. These are in processed food, in enhanced meats, in dark colas, in processed cheese, in convenience food.
• Natural phosphorus from animal foods is absorbed fairly well.
• Phosphorus from plants is absorbed poorly, because much of it is bound up as phytate. The phosphate in beans, nuts and grains largely passes through you.

The practical conclusion is a relief for most people: cutting processed food with phosphate additives is far higher yield than cutting lentils. Read the ingredients, and look for anything containing "PHOS".

How the diet differs by treatment

What to actually do

• Ask for a renal dietitian. Not a general dietitian, and not a leaflet. A renal dietitian is a standard part of the kidney team, and they are the single most under-used person in it.
• Take your real food diary, not a tidied-up version of it. They have seen everything, and they cannot help with a diary that is a work of fiction.
• Take your blood results. The diet follows the numbers, and the numbers change.
• Attack salt first, because it is the lever that moves fluid, blood pressure, cramps and how you feel after a session, all at once.
• Attack phosphate additives second, because it is the highest-yield change with the smallest cost to your diet.
• Do not start supplements, herbal remedies or a "kidney cleanse". Many are dangerous in kidney failure, particularly anything with potassium, phosphate, magnesium, or high-dose vitamin A or C.