Story
Potassium & Sodium
Last updated
In one pass Potassium stays inside the cell; sodium stays outside. Not this — Even drinking water makes you fat — Water has zero calories and cannot become fat. A 1-2 kg daily swing is water: glycogen holds 3-4 times its weight in water (Olsson & Saltin 1970), plus sodium retention and hormones. Watch the 2-week trend.
Educational content, not medical advice — consult a clinician.
Story path
Chapter 1
Potassium inside, sodium outside
Potassium stays inside the cell; sodium stays outside. That inside-outside concentration gap is the electricity nerves and muscles use to fire and contract.
The gap is held by an energy-burning protein in the cell membrane that keeps pushing sodium out and pulling potassium in: the sodium-potassium pump (Na⁺/K⁺ ATPase). Every cell has one. Without it, nerves cannot fire and muscles cannot contract.
Potassium and sodium both carry one positive charge; they are not a positive-and-negative pair. Their roles differ by location: potassium sits mostly inside the cell, sodium mostly outside, and the two opposing concentration gaps together make up the electrical system. Drinking lots of plain water after heavy sweating dilutes blood sodium; severe diarrhea drains potassium. When the gradient slips, nerve conduction, muscle contraction, and heart rhythm are all affected. If, during or after long exercise, headache and nausea are joined by confusion or seizures, blood sodium may have been diluted to a dangerous level: get emergency care right away (see Ions in exercise).
One level deeper: the concentrations on each side of the membrane, how much resting energy the pump burns, and why a heart drug acts on it.
The gap is held by an energy-burning protein in the cell membrane that keeps pushing sodium out and pulling potassium in: the sodium-potassium pump (Na⁺/K⁺ ATPase). Every cell has one. Without it, nerves cannot fire and muscles cannot contract.
Potassium and sodium both carry one positive charge; they are not a positive-and-negative pair. Their roles differ by location: potassium sits mostly inside the cell, sodium mostly outside, and the two opposing concentration gaps together make up the electrical system. Drinking lots of plain water after heavy sweating dilutes blood sodium; severe diarrhea drains potassium. When the gradient slips, nerve conduction, muscle contraction, and heart rhythm are all affected. If, during or after long exercise, headache and nausea are joined by confusion or seizures, blood sodium may have been diluted to a dangerous level: get emergency care right away (see Ions in exercise).
One level deeper: the concentrations on each side of the membrane, how much resting energy the pump burns, and why a heart drug acts on it.
Numbers · How big the gap is and what it costs
In numbers: potassium inside the cell is high (~140 mmol/L), and sodium outside the cell is high (~140 mmol/L), a mirror-image pair.The sodium-potassium pump (Na⁺/K⁺ ATPase) runs thousands of times a second on every cell. Each turn spends 1 , pushing 3 Na⁺ out and 2 K⁺ in. Added up across the whole body, the pump uses 20–30% of resting energy.
What it produces is a voltage across the cell membrane, called the resting membrane potential: about -70 mV (negative inside, positive outside), the standby state of nerves and muscles. A single nerve firing is called an action potential. Sodium channels open, Na⁺ rushes in, the membrane potential flips to +30 mV, and the signal travels on. Right after, potassium channels open, K⁺ rushes out, the membrane potential returns to baseline, and the cell is ready to fire again.
Mechanism · Why a heart drug targets this pump
The sodium-potassium pump is also an important drug target. The classic heart drugs called cardiac glycosides (such as digoxin and digitalis) work by partly inhibiting it. With the pump partly held back, sodium rises slightly inside heart-muscle cells. The sodium-calcium exchanger (Na⁺/Ca²⁺ exchanger), which uses the sodium gradient to move calcium out, then removes less calcium or even runs in reverse. More Ca²⁺ stays inside the cell, and the heart muscle contracts more strongly. Clinically, it is used to treat heart failure.Its therapeutic window is very narrow, meaning the effective dose and the toxic dose sit close together. Too much easily triggers arrhythmia, and toxicity is amplified when potassium is low or calcium is high (low potassium makes digoxin bind the pump more tightly). That is why ICU patients and people with heart failure on digoxin need close monitoring of blood potassium. Over-diuresis that drains potassium, combined with digoxin, is a classic dangerous pairing that can kill.
A toxicology note: plants such as Adonis (pheasant's eye), oleander, lily of the valley, and squill also contain cardiac glycoside compounds. If these materials are mistakenly used as folk "heat-clearing, detoxifying" herbal medicine, they can be fatal.
iom-2005-electrolytes
Chapter 2
BP: more than salt
More sodium raises blood volume and strengthens calcium signaling in the smooth muscle of blood vessels, so blood pressure rises. More potassium makes the kidneys pass more sodium into the urine (natriuresis), prompts the vessel lining (endothelium) to release nitric oxide, and relaxes the smooth muscle, so blood pressure falls. The two pull in opposite directions and set the result together.
So high blood pressure is not simply eating too much salt. In population studies, the sodium-to-potassium ratio tracks blood pressure more closely than sodium alone; this is an observed association. Modern diets have turned that ratio upside down: whole foods are high in potassium and low in sodium, while processed foods are high in sodium and low in potassium. And some people are especially sensitive to sodium.
One level deeper: who is sensitive to sodium, the grams guidelines give, what long-term follow-up found, and how many millimeters of mercury a produce-rich, low-sodium eating pattern (DASH) can take off blood pressure.
So high blood pressure is not simply eating too much salt. In population studies, the sodium-to-potassium ratio tracks blood pressure more closely than sodium alone; this is an observed association. Modern diets have turned that ratio upside down: whole foods are high in potassium and low in sodium, while processed foods are high in sodium and low in potassium. And some people are especially sensitive to sodium.
One level deeper: who is sensitive to sodium, the grams guidelines give, what long-term follow-up found, and how many millimeters of mercury a produce-rich, low-sodium eating pattern (DASH) can take off blood pressure.
Numbers · Who is salt-sensitive, what guidelines say
Some people are especially sensitive to sodium, called salt-sensitive: their blood pressure falls unusually far when they cut sodium. They are more common among people with high blood pressure, older adults, Black people, and people with diabetes or chronic kidney disease (); how large a share of the population they make up varies widely, because studies measure it differently. There is one pooled figure for the average effect of cutting salt: He 2013 combined 34 randomized trials (3,230 people), and eating about 4.4 g less salt a day lowered systolic blood pressure (SBP, the higher number in a reading) by about 5.4 mmHg on average in people with high blood pressure and by about 2.4 mmHg in people with normal blood pressure.WHO (2012) recommends that healthy adults keep sodium under 2 g a day (equal to 5 g of salt), while actual average intake worldwide is about 4.3 g of sodium a day (about 11 g of salt). US data from the National Health and Nutrition Examination Survey (NHANES) put average potassium intake at about 2.6 g a day: below the adequate intake () for men of 3.4 g, and roughly level with the AI for women of 2.6 g. Modern Western diets have a sodium-to-potassium ratio of about 2:1, while estimates of Paleolithic diets put it near 1:5, roughly a tenfold reversal.
Participants in TOHP (a set of hypertension-prevention trials) were later followed for 25 years, and that follow-up was an observational analysis: people who ate more sodium had more cardiovascular events, in a roughly straight-line relationship, and people who ate more potassium had fewer. This is an association and cannot prove cause on its own, but it points the same way as the ratio above: what matters is the whole diet, not any single mineral.
who-2012-sodiumhe-2013-bmj-salt-reduction
Evidence · DASH and other lifestyle changes
DASH (Dietary Approaches to Stop Hypertension) comes from an NIH-funded (RCT) published in 1997.It differs from a typical American diet in a few places: 8–10 servings of fruit and vegetables a day (versus about 4 in a typical diet); clearly more whole grains, low-fat dairy, legumes, and nuts; and clearly less red meat, sugary food, and sodium. The trial menu raised potassium to 4.7 g a day, with magnesium at 500 mg a day and calcium at 1240 mg a day. Those are the design amounts of the trial diet, not a target for everyone.
The effect shows within 4 weeks. In people with hypertension, systolic pressure fell by 11.4 mmHg on average and diastolic pressure by 5.5 mmHg, comparable to the usual drop from a single blood-pressure drug. A separate trial, DASH-Sodium (Sacks 2001), cut sodium further on the DASH diet: going from about 3.5 g to about 2.3 g a day lowered systolic pressure by only 1.3 mmHg more, and going on down to about 1.2 g lowered it by another 1.7 mmHg. In people with normal blood pressure the effect was much smaller (systolic about -3.5 mmHg).
Here are the common lifestyle measures for hypertension, with each one's rough effect on systolic pressure. They are listed roughly from largest to smallest; weight loss is counted per kilogram, so the more you lose, the larger the drop, and it does not slot neatly into the order:
1. DASH diet (about -11 mmHg)
2. Regular aerobic exercise (150 min/week, about -5 to -8 mmHg)
3. Cutting sodium (about -4 to -6 mmHg)
4. Raising potassium (about -4 to -5 mmHg)
5. Limiting alcohol (about -3 mmHg)
6. Losing weight (for people with overweight, body mass index > 25: about 1 mmHg for every 1 kg lost)
These figures come from different studies and compare only roughly. The measures are not mutually exclusive; done together, their effects partly add up, but not as a simple sum. A combined drop of 15–25 mmHg in systolic pressure when all of them are in place is a rough estimate. For some people with early hypertension, that may be enough to put off medication for now; whether to take medication is for a doctor to decide, based on overall risk.
Translated into Chinese eating, DASH roughly means fewer pickled vegetables and salt-cured fish; more leafy greens, soy foods, and fruit; whole grains in place of some white rice; less meat; and less sugar. There is no need to copy American ingredients: getting the proportions right is what counts.
appel-1997-nejm-dashsacks-2001-dash-sodium
Chapter 3
Processed food flips the balance
Whole foods mostly run high in potassium and low in sodium; ultra-processed foods mostly run the other way. That reversal is one of the main ways modern diets push blood pressure up.
Potassium comes into a meal inside intact plant cells; sodium is added by industry as a tool for flavor, preservation, and texture. So within a single meal, both ends of the scale get twisted the wrong way.
In practice: use less salt when cooking, skip salty soups, and eat less processed meat and more beans, tubers, and leafy greens. That is easier to act on than counting milligrams. Gram for gram, potato with its skin and avocado both carry more potassium than banana (see Potato · see Avocado).
One level deeper: potassium and sodium across food groups, where sodium hides, the large trial of replacing part of the salt with potassium chloride, and why banana is not the potassium champion.
Potassium comes into a meal inside intact plant cells; sodium is added by industry as a tool for flavor, preservation, and texture. So within a single meal, both ends of the scale get twisted the wrong way.
In practice: use less salt when cooking, skip salty soups, and eat less processed meat and more beans, tubers, and leafy greens. That is easier to act on than counting milligrams. Gram for gram, potato with its skin and avocado both carry more potassium than banana (see Potato · see Avocado).
One level deeper: potassium and sodium across food groups, where sodium hides, the large trial of replacing part of the salt with potassium chloride, and why banana is not the potassium champion.
Numbers · Food potassium, hidden sodium, salt swaps
Some high-potassium, low-sodium foods (mg per 100g, with the potassium-to-sodium ratio), approximately:White beans, sweet potato, potato (with skin): potassium ~500, sodium ~10, ratio 50:1Spinach, Swiss chard: potassium ~550, sodium ~80, ratio 7:1Avocado: potassium ~485, sodium ~7, ratio 70:1Yogurt (unsalted): potassium ~230, sodium ~50, ratio 4.5:1Banana: potassium ~360, sodium ~1, ratio 360:1Coconut water: potassium ~250, sodium ~105, ratio 2.4:1
Some typical high-sodium, low-potassium foods:
Instant noodles (one packet): sodium ~2000, potassium ~100, ratio 0.05:1; compared with the whole foods above, the ratio is reversed more than 100-foldCured meat, bacon, ham: sodium ~1500, potassium ~200Potato chips: sodium ~500, potassium ~1100. Potato is naturally high in potassium, so potassium still exceeds sodium; the problem is that the sodium is dozens of times higher than in fresh potato, almost all of it salt added in processingSoy sauce, 1 tablespoon (15 ml): sodium ~900, almost no potassiumPizza, fast food: sodium ~700–1500 per serving
Hidden sources of sodium are often underestimated: bread and breakfast cereals (salted during manufacture, and the single largest source of sodium in the American diet), processed meat and cheese, canned soup, sauces and salad dressings, and restaurant food (even dishes that do not taste salty can contain 1–2 g of sodium).
One more public-health tool worth knowing is salt substitute, in which potassium chloride (KCl) replaces part of the sodium chloride (NaCl). SSaSS (2021) was a cluster- in rural China (20,995 people, mostly middle-aged and older adults who had had a stroke, mean follow-up 4.74 years). In the villages assigned to the substitute, strokes and cardiovascular events were both less frequent. It is one of the few "salt swap" interventions backed by a large RCT. Salt substitute contains potassium, so people with chronic kidney disease or on potassium-sparing drugs should read Supplement caution before using it.
neal-2021-nejm-china-salt
Myth · Is banana the best potassium source?
"Banana is the best food for potassium" is a very common misconception. Line up the actual potassium content of common foods (mg per 100g):White beans (cooked) ~561 mgSpinach (cooked) ~558 mgSweet potato, cooked with skin ~475 mgSalmon ~490 mgAvocado ~485 mgWhite mushrooms ~396 mgYogurt (fat-free) ~234 mgBanana ~358 mg, actually mid-table rather than the champion
The current US adequate intake () for potassium is 3400 mg a day for men and 2600 mg a day for women, and bananas alone clearly fall short: one banana provides about 422 mg, far from the target. Eat varied food instead, such as oats, milk, and a banana at breakfast, bean soup at lunch, and roasted sweet potato, salmon, and salad at dinner, and going over the AI in a day is not hard.
Some high-potassium foods are surprising. Dried foods such as dried mushrooms and sun-dried tomatoes are concentrated sources. One medium potato has about 600–900 mg of potassium, more than a banana and up to about twice as much. Kelp and nori are high in potassium too, but their iodine is also extremely high, so they should not be eaten in large amounts. Coconut water, weight for weight, actually has less potassium than banana.
In practice: do not treat banana as your only potassium source. It is convenient, but not the first choice. Varied whole foods plus less processed food usually reach the potassium AI on their own. If you really need more potassium, food comes before supplements; the risks of supplements are covered in Supplement caution.
Chapter 4
Ions in exercise
Every muscle contraction during exercise swaps sodium and potassium, and the harder the effort, the faster the turnover. But sweat carries away mostly sodium; only a little potassium is lost.
So sodium is what needs replacing. For short sessions, water is enough; only long, heavy-sweating efforts call for extra salt. Drinking plain water on a schedule is more dangerous than drinking to thirst: diluted blood sodium is exactly the kind of low sodium commonly seen in marathon emergency care. Potassium rarely needs special replacement: glycogen breakdown during exercise releases potassium from inside cells, and everyday food usually covers the rest.
One level deeper: how much sodium sweat contains, how to replace it by session length, and how to prevent and treat the low blood sodium that comes from drinking too much.
So sodium is what needs replacing. For short sessions, water is enough; only long, heavy-sweating efforts call for extra salt. Drinking plain water on a schedule is more dangerous than drinking to thirst: diluted blood sodium is exactly the kind of low sodium commonly seen in marathon emergency care. Potassium rarely needs special replacement: glycogen breakdown during exercise releases potassium from inside cells, and everyday food usually covers the rest.
One level deeper: how much sodium sweat contains, how to replace it by session length, and how to prevent and treat the low blood sodium that comes from drinking too much.
Numbers · How much sodium sweat takes, when to add it
During hard exercise, the activity of the sodium-potassium pump (Na⁺/K⁺ ATPase) can reach 20 times its resting level.Sweat is mostly sodium and chloride. Its sodium concentration varies widely (~300–1200 mg/L) with the person, their training adaptation, and how much salt they usually eat. Its potassium concentration is low (~150 mg/L), and the total is small; chloride follows sodium; magnesium and calcium are only traces. Applied to one session: an hour of hard training with 1–2 L of sweat loses roughly 600–2400 mg of sodium and 150–300 mg of potassium. Sodium losses far exceed potassium losses, so sodium, not potassium, is what needs replacing.
Whether to replace electrolytes can be tiered by session length. Under 60 minutes, water is enough. For 60–90 minutes at moderate intensity, water plus some electrolytes will do, especially in the heat. For more than 90 minutes with heavy sweating (a marathon, long-distance cycling, hot yoga), you can add some sodium to your drinks. But keep one thing straight: the main cause of dilutional hyponatremia is drinking more than you sweat. Large amounts of plain water dilute blood sodium; severe cases bring seizures and loss of consciousness, and they are common in mass-marathon emergency care. Extra sodium cannot offset overdrinking; the real prevention is drinking to thirst, not on a schedule.
As for electrolyte drinks: most sports drinks carry about 200–500 mg/L of sodium, lower than sweat itself, which makes them essentially an industrial version of water with a little salt and sugar. If you want more sodium on long efforts, choose a higher-sodium drink or salt tablets, but only on the condition that you do not overdrink.
Red flag · Low blood sodium from overdrinking
Drinking so much during exercise that blood sodium is diluted is called exercise-associated hyponatremia (EAH). It is one of the most common medical emergencies in modern marathons and long-distance sport.The mechanism: long exercise, large amounts of plain water or low-sodium sports drink, and sodium lost in sweat together dilute blood sodium (< 135 mmol/L). In severe cases (< 125 mmol/L) the brain swells, called cerebral edema, as brain cells take on water; signs are headache, nausea, seizures, and altered consciousness, and it can be fatal. Almond 2005 took blood from 488 runners at the finish of the 2002 Boston Marathon: 13% had blood sodium ≤ 135 mmol/L, and 0.6% were at ≤ 120, a dangerous level. On multivariate analysis the independent associations were weight gain during the race (drinking more than was sweated out), a finishing time over 4 hours (a slower pace and longer time to drink) and a body mass index that was too high or too low; women were affected more often on simple comparison, but once these factors were accounted for, sex, whether people drank water or sports drinks, and use of painkillers were no longer independently associated. Slogans like "drink lots to stay hydrated" that encourage overdrinking are themselves one of the direct causes.
During or after a race, if headache and nausea are joined by confusion or seizures, get medical help immediately, at the course medical tent or an emergency department.
The 2015 international consensus led by Hew-Butler (the statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference) puts prevention on drinking rate: do not drink faster than you sweat (sweat rates vary widely between people and with the weather), and drinking when thirsty is safer than drinking on a schedule. On sodium, a common practice is to drink sodium-containing drinks or lightly salted water during long events with heavy sweating; sports drinks vary widely in sodium, and some carry little. As above, though, extra sodium does not replace drinking less.
Emergency care follows a few clinical rules. With mild symptoms and a clear mind, fluids are restricted and the person is observed while blood sodium recovers on its own. Severe cases (seizures, altered consciousness) are time-critical and need intravenous hypertonic saline (3% NaCl), not slow correction. Low-sodium IV fluids (for example D5W, a glucose drip) must never be given; they make the condition worse.
For recreational runners, on race day drinking enough is safer than drinking a lot: drink when thirsty, not on a schedule.
hew-butler-2015-eahalmond-2005-nejm-eah
Chapter 5
Supplement caution
With healthy kidneys, surplus potassium is excreted; potassium from food leaves by that route and almost never pushes blood potassium too high. High blood potassium (hyperkalemia) comes from potassium pills, potassium-retaining drugs, or kidney disease blocking that exit.
The highest risk is chronic kidney disease combined with ACE inhibitors or sartan-type blood-pressure drugs, or with diuretics such as spironolactone that make the kidney hold on to potassium. Salt substitutes containing potassium chloride need care in this group too.
Sodium has limits on its side as well: for healthy adults the target is still the upper limit in current guidelines, but there is no need to fear salt so much that you use none at all. An observational study (PURE) found higher risk among people eating very little sodium; that finding is still contested and is no reason to eat more salt. The strict sodium restriction that conditions such as heart failure and ascites from cirrhosis need should be done under a doctor's guidance.
For the great majority of people, the right move is more potassium from produce, legumes, and tubers, and less sodium from processed food. One level deeper: what blood potassium level is dangerous, who must not supplement potassium on their own, and whether lower sodium is always better.
The highest risk is chronic kidney disease combined with ACE inhibitors or sartan-type blood-pressure drugs, or with diuretics such as spironolactone that make the kidney hold on to potassium. Salt substitutes containing potassium chloride need care in this group too.
Sodium has limits on its side as well: for healthy adults the target is still the upper limit in current guidelines, but there is no need to fear salt so much that you use none at all. An observational study (PURE) found higher risk among people eating very little sodium; that finding is still contested and is no reason to eat more salt. The strict sodium restriction that conditions such as heart failure and ascites from cirrhosis need should be done under a doctor's guidance.
For the great majority of people, the right move is more potassium from produce, legumes, and tubers, and less sodium from processed food. One level deeper: what blood potassium level is dangerous, who must not supplement potassium on their own, and whether lower sodium is always better.
Clinical · Hyperkalemia thresholds, who must not self-dose
The core risk is hyperkalemia, blood potassium that is too high: above 5.5 mmol/L it can trigger arrhythmia, and above 7.0 mmol/L it can cause ventricular fibrillation or cardiac arrest outright; mortality under emergency treatment is high.These groups are at especially high risk if they supplement potassium on their own:
Chronic kidney disease ( stages 3–5), with reduced potassium excretionPeople on ACE inhibitors (ACEI), sartan-type drugs (), or sacubitril/valsartan for blood pressure or heart failure, drugs that themselves reduce potassium excretion by the kidneyPeople on potassium-sparing diuretics (spironolactone, amiloride), which directly make the kidney keep potassiumLong-term use of non-steroidal anti-inflammatory drugs (), which reduce blood flow to the kidneyDiabetic kidney disease, or blood glucose that stays poorly controlledAdrenal insufficiency (Addison's disease), with too little aldosteroneRhabdomyolysis (large-scale muscle breakdown) or severe tissue injury, which releases large amounts of potassium from inside cells
These people are better off not supplementing potassium on their own and should be careful with salt substitutes containing potassium chloride. Before eating large amounts of high-potassium food, they should also check their kidney function and medication list, and talk to a doctor when needed.
In practice: most people should get more potassium from food (produce, legumes, tubers) while cutting sodium (less processed food, fewer salty seasonings). People on medication or with kidney disease should ask their doctor before changing their diet and should not supplement potassium on their own. Athletes and people in high-sweat jobs should focus on replacing sodium, not potassium.
Evidence · Is lower sodium always better?
Eating less sodium means fewer cardiovascular events: this was once widely treated as settled. The PURE study (2014–2020) challenged that view, but the challenge itself is still contested.The classic view (WHO and the American Heart Association, AHA) is linear: sodium < 2 g/day (salt < 5 g), and the lower the sodium, the lower the blood pressure and the fewer cardiovascular events. PURE, a multinational observational cohort that estimated sodium intake from a single morning urine sample, saw a J-shaped curve instead. In its analysis of cardiovascular events (O'Donnell 2014 NEJM, 101,945 people in 17 countries), people at 7 g or more of sodium a day had more deaths and major cardiovascular events than those at 4–6 g, and so did people below 3 g; among people with hypertension, risk rose from 6 g. Later PURE analyses of potassium found that people who ate more potassium had lower risk, an observed association; from this the researchers concluded that the marginal gain from cutting sodium is smaller than the gain from raising potassium.
China's own figures are worth setting beside these, because they match neither: national standard WS/T 578.2—2018 sets sodium for adults aged 18–49 at an adequate intake () of 1500 mg/day and potassium at 2000 mg/day (sodium drops to 1400 from age 50).
One trap is easy to slide past here: an AI and an upper limit are not the same kind of number. An AI answers "have you had enough"; WHO's under-2 g answers "have you had too much". Comparing a sufficiency figure directly with a ceiling figure produces strange conclusions. When two numbers seem to disagree, first check whether they are even the same kind of quantity.
The J-curve remains contested. Critics point to several methodological problems: estimating 24h intake from a single urine sodium sample introduces error, and reverse causation (seriously ill people eat blandly, so their sodium intake is low) and samples with high body mass index () can also distort the results. AHA and WHO therefore still hold to < 2 g/day, judging that the left arm of the J mostly reflects interference from chronic disease. The PURE team's explanation is that very low sodium switches on the body's sodium-conserving renin-angiotensin-aldosterone system () and may come with insulin resistance. That is their hypothesis; it has not been shown directly.
What to do with this: PURE is an observational study, so its J-curve can serve only as contested background, never as a target. For healthy adults the target is still current guidance: WHO recommends sodium < 2 g/day (about 5 g of salt), and the US NASEM 2019 report set 2.3 g/day as the sodium intake for reducing chronic-disease risk (CDRR). Eat more potassium-rich food alongside. There is no need to fear sodium to the point of "no salt at all"; people who already have hypertension, especially if salt-sensitive, have even more reason to keep sodium down; athletes and people in high-sweat jobs should not push sodium too low. Wherever you sit on the curve, less processed food and more produce and legumes is almost always right: the sodium-to-potassium ratio improves on its own, which is more useful than agonizing over any exact milligram figure.
ws-t-578-2-2018-cn-dri-macromineralsmente-2018-pure-sodiumodonnell-2014-nejm-pure-sodium-events
Chapter 6
Water weight isn't fat
Glycogen binds water, and sodium holds on to water. The extra 1–2 kg on the scale when you wake up is almost always one of those two, not fat.
Water you drink has no calories and cannot turn into fat, so "even drinking water makes me fat" is literally wrong. Real fat change shows in the trend over a week or two, not in one morning's number.
One level deeper: why a kilogram of fat cannot appear overnight, how glycogen-bound water, sodium-held water, and the menstrual cycle each move the scale, and how to weigh yourself without being fooled by water weight.
Water you drink has no calories and cannot turn into fat, so "even drinking water makes me fat" is literally wrong. Real fat change shows in the trend over a week or two, not in one morning's number.
One level deeper: why a kilogram of fat cannot appear overnight, how glycogen-bound water, sodium-held water, and the menstrual cycle each move the scale, and how to weigh yourself without being fooled by water weight.
Numbers · Why 1 kg of fat cannot appear overnight
Why can 1 kg of fat not appear overnight? An energy ledger makes it clear: 1 kg of body fat equals about 7700 kcal of energy surplus. Gaining 1–2 kg of fat out of nowhere in one night would take 7700–15000 kcal of extra eating, which the body cannot do.So the 1–2 kg that swings within a day is not a fat ledger; it is body fluid moving around. It comes mainly from three things: water bound to glycogen, water held by sodium, and hormone swings before a period.
Mechanism · Glycogen water, sodium, the menstrual cycle
Glycogen-bound water: the body stores carbohydrate as glycogen, and each 1 g of glycogen binds 3–4 g of water (Olsson & Saltin 1970). Eat a high-carbohydrate meal and glycogen and water refill together, so weight goes up; eat low-carb for a few days and emptying glycogen takes its water along, so weight drops fast. That is why most of what comes off in the first few days of keto or carb-cutting is water.Sodium and body fluid: after a high-sodium meal (hotpot, barbecue, instant noodles), the body briefly holds extra water to keep blood sodium concentration steady, so the scale reads high the next day; once the extra sodium is excreted, the water follows and weight falls back. For how sodium affects body fluid and blood pressure, see BP: more than salt.
Hormones and the menstrual cycle: before a period, swings in progesterone and estrogen make some women hold 1–2 kg of extra water, which clears once that phase of the cycle passes.
Other causes: water stored in muscle during inflammatory repair after strength training, lower-leg swelling from high salt plus long sitting, and water retention from raised cortisol when sleep is short can all push weight up briefly.
In practice · Don't fight water weight
What this means for weight loss: do not be fooled by water weight.Do not weigh every day, and do not melt down over one day's swing: real fat change shows in the trend over 1–2 weeks, not in one morning's numberWeigh under the same conditions: in the morning, before eating, after using the toilet, in the same clothes, to cut the noise from water weightWatch the trend, and other measures too: weight, waist, photos, and how your clothes fit, taken together, are more reliable than a single numberDo not celebrate a fast early drop: most of what comes off in the first week or two is glycogen water, not fat; real fat loss is slow and steady
The scale measures how much water, fat, and everything else together you are carrying right now, and a jump within a day is almost all water. Do not fight water weight; watch the 2-week trend.
Related topics: Weight Management (don't only watch the scale) · Eating Less Without Going Short (nutrition while losing fat) · Carbs & Fiber (glycogen and carbohydrate) · in this story, BP: more than salt (sodium and body fluid).
References · 7
- National Institutes of Health, Office of Dietary Supplements. (2021). Potassium — Fact Sheet for Health Professionals. ods.od.nih.gov/factsheets/Potassium-HealthProfessional
- National Academies of Sciences, Engineering, and Medicine. (2019). Dietary Reference Intakes for Sodium and Potassium. National Academies Press. The PubMed book abstract (PMID 30844154) gives no reference values; it says the report updates the sodium and potassium DRIs with an expanded model that adds chronic-disease endpoints (the Chronic Disease Risk Reduction Intake). The numeric AIs and CDRRs were not re-read for this note (abstract). www.ncbi.nlm.nih.gov/books/NBK538102
- U.S. Department of Agriculture & U.S. Department of Health and Human Services. (2020). Dietary Guidelines for Americans, 2020-2025 (9th ed.). www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_Americans_2020-2025.pdf
- Strazzullo, P., et al. (2009). Salt intake, stroke, and cardiovascular disease: meta-analysis of prospective studies. BMJ, 339, b4567. 19 cohort samples from 13 prospective studies, 177,025 participants, 3.5-19 years of follow-up. Higher salt intake was associated with stroke (pooled RR 1.23, 1.06-1.43); total cardiovascular disease RR 1.14 (0.99-1.32; P = 0.07), significant (1.17) only after excluding one study. Observational (abstract, PMID 19934192). 10.1136/bmj.b4567
- Aburto, N. J., Hanson, S., Gutierrez, H., Hooper, L., Elliott, P., & Cappuccio, F. P. (2013). Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses. BMJ, 346, f1378. Higher potassium intake lowered systolic BP by ~3.5 mmHg in people with hypertension and was associated with lower stroke risk (RR 0.76). 10.1136/bmj.f1378
- Hargreaves, M., & Spriet, L. L. (2020). Skeletal muscle energy metabolism during exercise. Nature Metabolism, 2(9), 817–828. 10.1038/s42255-020-0251-4
- Olsson, K. E., & Saltin, B. (1970). Variation in total body water with muscle glycogen changes in man. Acta Physiologica Scandinavica, 80(1), 11-18. About 3-4 g of water is stored with each gram of muscle glycogen; a carbohydrate-rich diet raised total body water by ~2.2 L, attributed to glycogen storage. 10.1111/j.1748-1716.1970.tb04764.x