Category: Kidney disease · Renal nutrition · Sodium
Stage 4–5 CKD and Thai Steamed Mackerel: Hidden Sodium in Salted Fish, Swelling and Fluid in the Lungs, How Much Protein Fits, and Fresh Fish to Choose Instead
AI Overview / Quick Answer (BLUF)
Thai steamed mackerel is cooked in brine. USDA lists 4,450 mg sodium per 100 g salted mackerel versus 90 mg in fresh mackerel, while CKD guidance caps sodium below 2,000 mg a day. Excess salt drives swelling, high blood pressure and lung fluid; fresh fish steamed with herbs is safer.
the KDIGO 2024 CKD guideline,
the KDOQI nutrition guideline,
the review of salt reduction in kidney disease
and background on healthy eating with chronic kidney disease from NIDDK.
Warning signs ·
Sodium in mackerel ·
Salt and swelling ·
Protein and phosphorus ·
Fresh fish and cooking ·
Comparison table ·
FAQ
From a kidney patient group: can stage 4–5 CKD still include steamed mackerel?
One member caring for stage 4–5 kidney disease, not yet on dialysis, asked whether steamed mackerel, a staple side dish at home, is still okay,
and which fish to eat instead if not. Several others in the group asked whether boiling it in fresh water first helps, and which kinds of swelling or breathlessness need urgent care.
The short answer: the main problem with steamed mackerel is the salt, not the fish. Mackerel flesh is good protein, but cooking it in brine makes it high in sodium.
At stages 4–5 the kidneys clear salt and water poorly, so extra salt turns into retained fluid. If pink salt or fish bones are also on your mind, see
Stage 4 CKD, fried tilapia and pink salt.
Warning signs — seek medical care urgently
Direct answer: in stage 4–5 CKD, the fast dangers of salt overload are fluid in the lungs and a hypertensive crisis, while high potassium can come from salt substitutes or potassium-rich foods
(McMahon 2021,
Te Dorsthorst 2019)
Go to hospital now, or call emergency services (1669 in Thailand)
- Breathlessness, unable to lie flat, waking at night to sit up, or coughing pink frothy sputum — possible pulmonary edema
- Blood pressure of 180/120 or higher with severe headache, chest pain, blurred vision, limb weakness or slurred speech
- Palpitations, an irregular pulse, or whole-body muscle weakness — possible high blood potassium
- Confusion, drowsiness, seizures, or vomiting so much you cannot eat
See a doctor within a few days
- Pitting swelling of the legs or ankles, a puffy face in the morning, or gaining several kilograms within a few days
- Home blood pressure of 140/90 or higher on several readings — not an emergency without symptoms, but above target; bring your readings to your doctor
- Clearly less urine, or more foamy urine
- Very painful skin sores that are dusky purple or hard and plaque-like — rare, mostly in people on dialysis; have a doctor check promptly
2. Why salt causes swelling, high blood pressure and fluid in the lungs at stages 4–5
Direct answer: when the kidneys excrete less sodium, the body holds water to dilute the salt, so extracellular fluid expands.
The result is leg swelling, higher blood pressure and, when overload is severe, fluid seeping into the lungs. Randomized trials show that cutting salt in kidney disease lowers both blood pressure and protein leak in the urine
(McMahon 2013,
McMahon 2021)
Salt pulls water with it
A double-blind randomized crossover trial in 20 people with hypertensive stage 3–4 CKD found that during salt restriction, average blood pressure fell by 10/4 mmHg,
extracellular fluid volume fell, and urine protein and albumin fell. The authors noted the effect was larger than in people without kidney disease,
meaning people with CKD are particularly salt sensitive
(McMahon 2013)
The overall picture from 21 studies
A Cochrane systematic review of 21 studies with 1,197 people found that cutting salt by about 4.2 g a day (1,690 mg sodium)
lowered blood pressure by 6.91/3.91 mmHg with high-certainty evidence, and lowered urine albumin by 36% in earlier-stage CKD.
It also found more symptomatic low blood pressure (RR 6.70), so people on several blood pressure medicines should cut salt under their doctor’s follow-up
(McMahon 2021)
A salty diet makes kidney-protecting medicine work less well
An analysis of 500 people with non-diabetic CKD on an ACE inhibitor (ramipril) found that the high-salt group developed kidney failure at 18.2 per 100 patient-years,
compared with 6.1 in the low-salt group, and the medicine’s protein-lowering effect was blunted even though blood pressure was similar. High salt in this study meant more than 14 g of salt a day
(Vegter 2012)
Blood pressure targets, and when it becomes an emergency
KDIGO 2021 proposes a systolic target below 120 mmHg, using standardized office measurement, for most people with CKD not on dialysis, if tolerated.
Each person’s actual target is set by their own doctor
(KDIGO 2021)
An emergency is 180/120 or higher with symptoms such as severe headache, chest pain, blurred vision or breathlessness, or any signs of pulmonary edema regardless of the reading.
Swelling, breathlessness, high blood pressure or less urine: what level are you at?
Analyze your severity level and receive personalized guidance from our Advisory team. This score helps sort kidney-care warning signs into
watch at home, book a doctor, or go to hospital now. It is not a diagnosis and does not replace blood tests; use it together with the warning-sign list above.
3. Protein and phosphorus in fish: how much fits at stages 4–5?
Direct answer: fresh fish is a suitable protein, but the amount matters. KDOQI 2020 recommends 0.55–0.6 g protein per kg body weight per day
for people with stage 3–5 CKD not on dialysis and without diabetes, under a dietitian’s supervision, while KDIGO 2024 suggests 0.8 g/kg/day
(KDOQI 2020,
KDIGO 2024)
Example protein budget for a 60 kg person
At 0.55–0.6 g/kg this is about 33–36 g protein a day; at 0.8 g/kg it is about 48 g a day.
100 g of fresh tilapia has 20.1 g protein, and rice, vegetables and eggs in other meals add protein too, so fish at each meal is usually about 40–60 g.
Each person’s figure depends on stage, diabetes and nutritional status, and should be calculated by a dietitian.
Without diabetes it is 0.55–0.6, or 0.28–0.43 with keto-acid analogues under close monitoring,
and cutting protein too far on your own risks protein-energy wasting. Once dialysis starts, protein needs rise to 1.0–1.2 g/kg/day.
Table: protein targets by situation
Based on KDOQI 2020 and KDIGO 2024; use together with a dietitian.
| Situation | Protein per day | Example, 60 kg | Cautions |
|---|---|---|---|
| CKD 3–5, not on dialysis, no diabetes | 0.55–0.6 g/kg (KDOQI 2020) | 33–36 g | Needs enough energy, 25–35 kcal/kg, so muscle is not broken down |
| CKD 3–5, not on dialysis, with diabetes | 0.6–0.8 g/kg (KDOQI 2020) | 36–48 g | Manage blood sugar at the same time |
| Very low protein with keto-acid analogues | 0.28–0.43 g/kg (KDOQI 2020) | 17–26 g | Only under doctor and dietitian monitoring |
| General guidance, CKD 3–5 (KDIGO 2024) | 0.8 g/kg; keep below 1.3 | 48 g | Frail older adults may need more |
| Hemodialysis or peritoneal dialysis | 1.0–1.2 g/kg (KDOQI 2020) | 60–72 g | Dialysis removes some protein, so intake must rise |
Phosphorus per gram of protein in fish
Fresh mackerel has about 11.7 mg phosphorus per gram of protein and fresh tilapia about 8.5 mg. In people on hemodialysis,
eating at a ratio of 16 mg or more per gram of protein was associated with a 1.99-fold mortality risk
(Noori 2010).
Fresh fish flesh therefore sits in the moderate range. The bigger concerns are processed fish with phosphate additives, which are almost fully absorbed,
and eating soft bones or small whole fish, which add both calcium and phosphorus
(Benini 2011,
Kalantar-Zadeh 2010)
Vascular calcification and calciphylaxis
Blood phosphorus that stays high for months to years is linked to calcium deposits in blood vessels and weaker bones. Calciphylaxis is a rare condition,
mostly in people on dialysis, in which small vessels under the skin calcify and block, causing very painful sores. It is dangerous and has many contributing factors;
it does not come from one meal of mackerel
(Nigwekar 2018)
Phosphorus control is judged from blood-test trends with a nephrologist.
4. Fresh fish and cooking methods to use instead
Direct answer: choose fresh fish, steam or boil it, and use herbs instead of salt and fish sauce.
This keeps the same protein while sodium drops from thousands to tens of milligrams per 100 g
(NIDDK,
KDIGO 2024)
Fresh fish that are easy to find
- Tilapia, red tilapia, snakehead, sea bass: white flesh, low in sodium when fresh; pick cuts without many tiny bones
- Fresh mackerel: buy it before brine cooking and steam it at home, keeping the omega-3 fats without factory salt
- Limit as regular foods: basket-steamed mackerel, salted fish, dried fish, fermented fish, fish balls, imitation crab and canned fish in sauce
Season with herbs instead of salt
Steam or boil fish with galangal, lemongrass, kaffir lime leaves, garlic and black pepper, and squeeze lime at the table for aroma and flavor without added salt.
If you must use fish sauce, measure it by the teaspoon: 1 teaspoon has about 470 mg sodium, and it counts toward the daily total.
People with high blood potassium should ask a dietitian about the amount of herbs and lime juice, even in small quantities.
How much does boiling or soaking in fresh water help?
Rinsing or boiling in fresh water removes some surface salt, but no study has measured how much sodium this removes from Thai steamed mackerel.
Research on desalting salted cod uses cold-water soaking over days, testing up to 72 hours, and warns that soaking above 10 °C risks bacterial growth
(Oliveira 2015).
Boiling it off two or three times in a home kitchen removes an unknown amount of salt, and should not be treated as permission to eat it regularly.
keep the rest of that day’s meals unsalted, and weigh yourself the next morning to see whether swelling has increased.
Salt substitutes and reduced-sodium sauces
A review of 44 reported episodes of diet-induced high potassium found salt substitutes caused 12, with an average potassium level of 8.2 mEq/L
(Te Dorsthorst 2019).
Check labels for potassium chloride and ask your doctor before use.
Steps to switch from steamed mackerel to fresh fish
5. Comparing ways to control salt, fluid and blood pressure at stages 4–5
Direct answer: dietary salt control is the foundation that helps blood pressure medicines and diuretics work better.
Boiling off salt or using salt substitutes are not safe shortcuts
(Vegter 2012,
KDIGO 2021)
Table: diet, medicines and habits for controlling salt and fluid
Medicines are listed by generic name and used only as your own doctor directs.
| Approach | How it helps | Evidence | Cautions |
|---|---|---|---|
| Keep sodium below 2,000 mg a day | Reduces extracellular fluid, blood pressure and protein leak | KDIGO 2024, McMahon 2013, McMahon 2021 | People on several blood pressure medicines may get dizzy from low pressure; monitor readings |
| Fresh fish steamed or boiled with herbs instead of steamed mackerel and salted fish | Same protein, dozens of times less sodium | USDA FDC, NIDDK | Keep within the protein budget; watch soft bones |
| ACE inhibitors or ARBs (e.g. ramipril, losartan) | Lower blood pressure and protein leak, slowing kidney decline | KDIGO 2021, Vegter 2012 (a salty diet blunts the effect) | Check potassium and creatinine as scheduled |
| Loop diuretics (e.g. furosemide) | Remove salt and water, easing swelling and lung fluid | Used at the doctor’s discretion in advanced CKD | Work less well with an ongoing salty diet; watch for dehydration and electrolyte problems |
| Fluid limits as set by your doctor | Reduce overload in people who pass little urine | Adjusted to each person’s urine output | Salty food causes thirst, making fluid limits harder |
| Boiling or soaking steamed mackerel in fresh water | Removes some surface salt | Not measured in Thai steamed mackerel (Oliveira 2015 studied salted cod) | Unknown reduction; only for occasional eating |
| Potassium chloride salt substitutes | Lower sodium in cooking | Te Dorsthorst 2019 (reports of high potassium) | Not for self-use at stages 4–5; risk of dangerous heart rhythms |
Beliefs worth correcting
Steamed mackerel is not fried, so it is not salty
“Steamed” describes how it is cooked, but most basket-steamed mackerel goes through strong brine, so its sodium is clearly higher than fresh fish even without oil.
Boil it off two or three times and you can eat it every day
This removes some salt, but by an unknown amount, and it has not been measured in Thai steamed mackerel. Fresh fish gives clearer control over sodium.
All sea fish are bad for the kidneys
Not true. Fresh mackerel has 90 mg sodium per 100 g, similar to freshwater fish; the problem is salt preservation. Purines matter for people with gout or high uric acid, which is a separate conversation with your doctor.
A reading of 140/90 means go to the emergency room now
That reading is above target and needs a doctor’s appointment, but an emergency is 180/120 or higher with symptoms, or signs of fluid in the lungs.
Low-sodium salt is a safe swap
Many low-sodium salts use potassium instead, which risks high potassium at stages 4–5. Ask your doctor before using one.
The less protein, the slower the kidneys decline
Lowering protein reduces waste products, but if energy and protein fall too low, the body breaks down muscle. Aim for the budget your dietitian calculates.
Frequently Asked Questions (FAQ)
Can people with stage 4–5 CKD eat steamed mackerel?
Not as a regular food. Thai steamed mackerel is cooked in brine. USDA lists salted mackerel at 4,450 mg sodium per 100 g, while fresh mackerel has only 90 mg, and KDIGO 2024 advises people with CKD to keep sodium below 2,000 mg a day. Thai steamed mackerel is likely less salty than dried salted mackerel, but it is still clearly saltier than fresh fish. If you want it occasionally, eat no more than half a small fish, skip extra fish sauce, and make fresh fish your everyday choice.
Why does steamed mackerel carry hidden sodium, and how does it cause swelling?
The hidden sodium comes from the brine used to cook and preserve the fish, not from visible salt crystals. When the kidneys excrete less sodium, the body holds water to dilute it, so extracellular fluid expands, causing leg swelling, weight gain and higher blood pressure. Severe overload pushes fluid into the lungs and causes breathlessness. A trial in stage 3–4 CKD found salt reduction lowered average blood pressure by 10/4 mmHg and reduced extracellular fluid volume.
How much does boiling or soaking in fresh water reduce the salt?
It removes some surface salt, but no study has measured how much sodium it removes from Thai steamed mackerel. Desalting research on salted cod uses cold-water soaking over days, testing up to 72 hours. Boiling it off two or three times in a home kitchen is therefore not permission to eat it regularly; fresh fish gives clearer control over sodium.
Which fresh fish suit stage 4–5 CKD?
Fresh white fish such as tilapia, red tilapia, snakehead and sea bass, or fresh mackerel that has not been brine-cooked, are all low in sodium when fresh. 100 g of fresh tilapia has 52 mg sodium and 20.1 g protein. Steam or boil them with galangal, lemongrass, kaffir lime leaves and garlic, with a squeeze of lime instead of salt and fish sauce. Limit soft bones and processed fish such as fish balls and imitation crab, which often carry salt and phosphate additives.
How much protein should someone with stage 4–5 CKD eat a day?
KDOQI 2020 recommends 0.55–0.6 g per kg body weight per day for people with stage 3–5 CKD not on dialysis and without diabetes, and 0.6–0.8 g for those with diabetes, while KDIGO 2024 suggests 0.8 g/kg/day. A 60 kg person therefore gets about 33–48 g a day, including protein from rice and other foods. Energy must be adequate at 25–35 kcal/kg, and protein needs rise once dialysis starts. A dietitian should calculate each person’s figure.
Can low-sodium salt or salt substitutes be used instead?
Not on your own at stages 4–5. Many salt substitutes use potassium chloride, which damaged kidneys clear poorly. A review of 44 reported episodes of diet-induced high potassium found salt substitutes caused 12. Very high potassium can cause dangerous heart rhythms. The safer route is seasoning with herbs and checking labels for potassium chloride.
Does a blood pressure of 140/90 mean going to the emergency room?
Without symptoms it is not an emergency, but it is above the KDIGO 2021 target, which proposes a systolic pressure below 120 mmHg with standardized measurement for most people with CKD. Log your readings and book a doctor’s appointment. An emergency is 180/120 or higher with severe headache, chest pain, blurred vision, limb weakness, or breathlessness that stops you lying flat.
What kind of swelling or chest tightness needs urgent hospital care?
Go to hospital now or call emergency services (1669 in Thailand) for breathlessness, inability to lie flat, waking at night to sit up, pink frothy sputum, chest pain, palpitations, an irregular pulse, or whole-body muscle weakness. See a doctor within a few days for pitting leg swelling, gaining several kilograms within a few days, or clearly less urine.
Scientific Mechanism
Why stage 4–5 CKD is salt sensitive: as the number of working nephrons falls, the amount of sodium the kidneys can filter out each day falls with it.
Excess sodium stays in the extracellular fluid; the body responds with thirst and water retention, so blood volume and blood pressure rise.
A trial in stage 3–4 CKD found the blood pressure effect of salt reduction was larger than in people with normal kidneys
(McMahon 2013)
Salt and kidney-protecting medicine: ACE inhibitors and ARBs lower pressure inside the kidney’s filtering units, reducing protein leak.
With high salt intake, their protein-lowering effect is blunted and the risk of kidney failure rises, even at similar blood pressure
(Vegter 2012)
From fluid overload to pulmonary edema: as extracellular fluid keeps expanding, pressure in the lung capillaries rises,
fluid seeps into the spaces around the air sacs, and oxygen exchange worsens, causing breathlessness especially when lying flat. This is why it needs urgent treatment.
Potassium from salt substitutes: the kidneys are the main route for potassium excretion. With advanced CKD plus an ACE inhibitor or ARB,
that capacity falls further, so potassium chloride in salt substitutes can raise blood levels enough to disturb the heart’s electrical conduction
(Te Dorsthorst 2019)
Compiled and reviewed by Asst. Prof. Dr. Norawit Raatpiboon
Academic References (E-E-A-T)
- KDIGO CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int 2024 (PMID 38490803)
- Ikizler TA et al. KDOQI Clinical Practice Guideline for Nutrition in CKD: 2020 Update. Am J Kidney Dis 2020 (PMID 32829751)
- Cheung AK et al. Executive summary of the KDIGO 2021 Clinical Practice Guideline for the Management of Blood Pressure in Chronic Kidney Disease. Kidney Int 2021 (PMID 33637203)
- McMahon EJ et al. A randomized trial of dietary sodium restriction in CKD. J Am Soc Nephrol 2013 (PMID 24204003)
- McMahon EJ et al. Altered dietary salt intake for people with chronic kidney disease. Cochrane Database Syst Rev 2021 (PMID 34164803)
- Vegter S et al. Sodium intake, ACE inhibition, and progression to ESRD. J Am Soc Nephrol 2012 (PMID 22135311)
- Te Dorsthorst RPM et al. Review of case reports on hyperkalemia induced by dietary intake: not restricted to chronic kidney disease patients. Eur J Clin Nutr 2019 (PMID 29588531)
- Noori N et al. Association of dietary phosphorus intake and phosphorus to protein ratio with mortality in hemodialysis patients. Clin J Am Soc Nephrol 2010 (PMID 20185606)
- Benini O et al. Extra-phosphate load from food additives in commonly eaten foods: a real and insidious danger for renal patients. J Ren Nutr 2011 (PMID 21055967)
- Kalantar-Zadeh K et al. Understanding sources of dietary phosphorus in the treatment of patients with chronic kidney disease. Clin J Am Soc Nephrol 2010 (PMID 20093346)
- Nigwekar SU et al. Calciphylaxis. N Engl J Med 2018 (PMID 29719190)
- Oliveira H et al. Quality changes during cod (Gadus morhua) desalting at different temperatures. J Sci Food Agric 2015 (PMID 25378287)
- USDA FoodData Central — Fish, mackerel, salted (FDC ID 168149); Fish, mackerel, Atlantic, raw (175119); Fish, tilapia, raw (175176); Sauce, fish, ready-to-serve (174531) · NIDDK — Healthy Eating for Adults with Chronic Kidney Disease
Medical Disclaimer
This article provides general educational information on sodium, protein and fish choices for people with stage 4–5 chronic kidney disease. It is not a diagnosis, a prescription or a personal treatment plan.
Nutrient values come from databases; actual amounts depend on the fish, the brine recipe and the cooking method. Medicines are named by generic name for education only.
Do not start, adjust or stop blood pressure medicines, diuretics or any other medicine without your own doctor. Plan meals with a nephrologist and a dietitian. In an emergency, call your local emergency number (1669 in Thailand).