Organizing the Body Through Daily Habits — Part 2 of 3
This is the second of three pieces in the series Organizing the Body Through Daily Habits. The series answers a question I am often asked in Rolfing sessions: what can be done in ordinary daily life? Part 2 takes up water and salt.
Water bears on posture
Since June 2015, I have offered Rolfing sessions in Shibuya.
Water is said to make up about seventy percent of the body. Muscle, too, is close to seventy percent water. Which means that when water is not being taken in adequately, it shows in the muscles — that is, in posture — and in how the brain works. The bacteria living in the gut need water to live as well.
This piece looks at how to take water in, from these angles.
How to judge whether water is short How the body takes water in How to take water in, in practice How to think about the kidneys and water Why water needs salt
Telling whether water is short
The Huberman Lab podcast offers two checks for whether you have taken in enough water.
Pinch the skin at the fingertip; it does not return within five seconds. Press a nail; the colour does not change within a second.
If either applies, water is likely short.
Here the ground is less firm than it looks.
Clinically these two are known as skin turgor and capillary refill time, and both have long been in use. But their accuracy as tests for dehydration is known to be poor. Systematic reviews find that capillary refill time and skin findings have limited utility in diagnosing dehydration or assessing its severity. Tachycardia, low blood pressure, dry mucous membranes, sunken eyes — the same holds; all have poor diagnostic accuracy.
Age matters most of all. Skin loses elasticity with age, so in older adults the skin may take twenty seconds to return without any dehydration at all. A review found that in people over sixty-five, skin turgor on its own is not effective, and nursing textbooks state plainly that research has shown it is not a good indicator. In children, it has been concluded to be only moderately accurate.
It costs nothing and hurts no one, so there is no harm in trying. But it does not settle whether you are drinking enough.
How the body takes water in
To talk about water, it helps to look at how it is taken into the body.
When we drink, water enters by two routes. The first is diffusion. The second is active transport using a protein called aquaporin. The first is slow, the second fast. Water taken as a drink is absorbed in the small intestine, where aquaporins do the work.
Water also moves the other way, out into the organs. The enzymes needed for digestion and absorption — gastric acid, pancreatic juice, intestinal juice — are mostly water. Aquaporins carry water out of the body’s tissues and into the organs, and digestion proceeds. Tears are water leaving through the eyes, and they use aquaporins too.
The fascia that Rolfing works with has aquaporins as well.
When a session works with fascia, movement improves — because water comes into the fascia and makes it easier to move. I feel the importance of water in the course of giving sessions.
Water reaching ligaments and bone, by contrast, seems to arrive by the first route, diffusion.
How much to drink
In hot weather we sweat. To keep body temperature from rising, the body uses water to carry heat out through the skin. That costs water. We lose 200 to 500 millilitres in sweat during sleep, and more in the morning through urine.
Andy Galpin, a sports trainer and university professor, advises replacing 400 to 800 millilitres of water early in the morning. He further recommends taking an average of two millilitres per kilogram of body weight every fifteen to twenty minutes — 120 millilitres for someone of sixty kilograms — over ten hours, roughly two litres. It does not all have to be drunk on its own; water can come from food. Taking in carbohydrate and salt also helps the body hold water.
In my own experience, on mornings when I have not had enough water my head does not work properly, and this approach improved that.
Let me set another view alongside it.
Peter Attia, a physician specialising in longevity medicine, is wary of fixed targets. He takes issue with the “eight glasses a day” rule and rejects the assumption that completely clear urine means optimal hydration. Taking in water in excess, without individualising, dilutes serum sodium and raises the risk of hyponatremia.
The figure he offers is two to three litres — with foods high in water, fruit, vegetables, soup, and other drinks counted within it. And the way to judge is not adherence to a fixed target but thirst and the colour of urine. Pale yellow as the marker.
Within the same territory, the advice differs.
I do not think this is a case of one side being wrong. Galpin is a trainer, and setting targets and getting people to hit them is the work. Attia is a physician, and watching the margin of safety for each patient is the work. Where each stands shows up in how the numbers come out.
The kidneys rest too
Why is taking water within ten hours recommended?
As the last piece described, we have an internal clock, and the kidneys fall under it. The body is not open around the clock; after about ten hours of work it moves toward rest. If the kidneys, which make urine, work through the night, night-time urination follows. To avoid that, water is worth thinking about within a ten-hour span.
Why salt
To take water in, one more thing is needed: paying attention to salt.
For two reasons.
First, blood is held at a set salt concentration, and trouble follows if it goes either low or high.
Second, salt holds water. More salt, more retention; less salt, more loss. So however much water you drink, without enough salt it gets excreted.
By “salt” here I mean not only sodium chloride but the minerals more broadly — magnesium and potassium included.
The salt concentration of the blood is monitored by a part of the brain called the OVLT. When the water content of the blood falls (lowering blood pressure), or when salt is low, it prompts replenishment. When blood pressure or salt rises, the kidneys excrete salt.
How much to take — divided here too
So how much salt should one take?
On the Huberman Lab video, Dr. James DiNicolantonio says 8 to 12 grams of salt a day is what is needed — 1.5 to 2 times the amount recommended in the United States. A teaspoon and a half to two teaspoons.
Here too, the ground is less firm than it looks.
DiNicolantonio’s argument is set out in a book called The Salt Fix, which has been examined within a framework for evaluating the content of books. The conclusion there was that the references cited do not convincingly support the claim that diets restricting sodium to the recommended range are harmful to cardiovascular and metabolic health. The score came to one out of four.
There are specific points as well. The observational studies the book draws on carry methodological problems, none of which are acknowledged in the book. The very low sodium intakes used in many of the trials fall below what guidelines describe, and so do not test what “keeping below 2,300 milligrams” actually means. And a meta-analysis of six prospective cohort studies found a dose-response relationship across the range of two to six grams a day: for each gram above two, cardiovascular risk rises.
The Japanese context is worth setting out. The WHO recommends five grams a day. The Ministry of Health, Labour and Welfare sets targets of under 7.5 grams for men and under 6.5 grams for women. Eight to twelve grams sits above these.
Attia’s position differs here too. He holds that drinking water alone, without electrolytes, can itself be a problem — but he limits who needs to supplement: people who sweat heavily, people on low-carbohydrate diets, people training at high intensity.
A researcher gives the mechanism, a trainer gives the number, a physician limits who it applies to. The three appear to be saying different things, but I think they are looking from different places.
Last time I wrote that there is no single answer to what the right diet is. The same holds for salt. It varies with how much you sweat, what you eat, the state of your blood pressure. There is no way around checking against your own body.
For those restricting carbohydrate
Attia’s mention of “people on low-carbohydrate diets” is worth taking further.
Carbohydrate holds water in the body. There is a mechanism here.
Carbohydrate is stored as glycogen in muscle and liver, and roughly three grams of water bind to every gram of glycogen. An adult can store four to five hundred grams of glycogen, which puts something like a litre and a half of water hanging off it.
Protein and fat have no store of water in this form.
Start restricting carbohydrate and weight can drop sharply in the first week. Much of that is glycogen and the water bound to it, leaving.
And there is a second route, on the salt side. Restrict carbohydrate and the body handles electrolytes differently. With insulin low, the kidneys excrete more sodium — a process called natriuresis. And because sodium sits in a delicate balance with the other electrolytes, losing it disturbs them as well.
Not only water but salt goes out with it. That is why anyone restricting carbohydrate does well to pay attention to water and salt.
The water in glycogen was not a reservoir
Let me bring in one study here, which I found interesting.
If three grams of water bind to every gram of glycogen, a thought follows. As glycogen is used up during a marathon, the water bound to it would be released. Something like 1.2 litres might become available. Fill your glycogen before you run, and you have a reserve against dehydration.
In 2017, someone measured this.
The osmolality of glycogen and potassium phosphate mixtures at a two percent concentration came out at 265 against a predicted 267. Almost identical. Which is to say that the water bound to glycogen is fully available to all the ions, and behaves as part of the body’s larger osmotic system. At higher concentrations, ten to twenty percent could be considered protected, but the majority followed ordinary osmotic considerations.
And in a calculation assuming a two-litre dehydration, the advantage to plasma volume from starting exercise glycogen-replete came to 1.57 percent — fifty-five millilitres.
The conclusion: glycogen-associated water does not appear as a separate reservoir, and cannot uniquely replete water lost during dehydration.
The trip out works; the trip back does not. That restricting carbohydrate depletes glycogen and costs water is correct. That storing glycogen gives you something to draw on when dehydrated did not hold.
The phrase “bound water” made it sound as though there were water set apart. Measured, that water turned out to be inside the body’s system along with everything else, indistinguishable from the rest.
Three years of restricting carbohydrate
Attia was in strict nutritional ketosis for three years, from 2011 to 2014. He is also a long-distance open-water swimmer. Finding early signs of metabolic dysfunction while competing in endurance sport is what took him there.
He writes that during those three years he was leaner and in better shape, mentally and physically, than at any other period of his adult life. His biomarkers were as good as they had ever been.
He did not stop out of doubt about its effects. He wanted to eat more vegetables. Meeting a target of 4,500 calories a day meant things like getting through a tub of sour cream. And it did not set his children a good example of balanced eating.
What he writes about the transition, though, is useful here. Moving onto a ketogenic diet, many people struggle to adapt. Difficulty sleeping, difficulty exercising, general fatigue. One reason is that the body is not yet fat-adapted, and has to manage a different balance of water and electrolytes brought about by restricting carbohydrate.
In the low-carbohydrate field, the symptoms of sodium shortfall during the transition are given as fatigue, weakness, headache, and difficulty concentrating. Short potassium brings muscle cramps and palpitations; short magnesium brings cramps at night or after exercise. The suggested remedy is to add sodium through broth or bouillon for the first week or so.
Whether restricting carbohydrate is a good idea is not what I am addressing. But if you are going to start, paying attention to water and salt follows from the mechanism.
On magnesium
Alongside sodium chloride, magnesium cannot be left out when thinking about salt.
Magnesium takes part in a great many enzyme reactions. The relaxation of muscle, the formation of heart muscle, the damping of nervous excitation — the range it touches is wide. So a shortfall reaches widely as well. It is known to work together with vitamins D and K. Magnesium shortfall is noted worldwide.
Sea salt and rock salt are high in magnesium. Among sea salts, Nuchimasu and Yukishio are among the higher ones. As for rock salt, it is worth looking into on your own.
Personally, I use nigari (Tenkai no Nigari) in cooking, and put Epsom salt in the bath, as ways of adding magnesium.
As supplements, there are magnesium citrate, magnesium threonate, and magnesium malate, among others.
Potassium, sodium, caffeine
Among the salts, sodium and potassium work together in the body and play an important part in carrying information through the nervous system. How much is recommended depends on what you eat.
Tea, coffee, chocolate and other things containing caffeine are diuretic. So after caffeine, it helps to keep in mind taking 1.5 times the water along with a little salt.
Salt and sugar are regulated differently
Salt and sugar are known to be regulated by different mechanisms in the body.
With sugar, the more you take, the more you want and the more you take. Positive feedback. With salt, the more you take, the more the body signals to cut back, and it regulates well. Negative feedback.
But in processed foods where salt and sugar are mixed — rice crackers, say — the sugar keeps the brain from registering how much salt has come in, and consumption goes unchecked. What is actually the problem is processed food together with salt.
Understand this and cut down on sugar and processed food, and salt itself becomes less of a concern.
Against heat illness — palms, soles, and forehead rather than the neck
In hot weather, body temperature rises easily.
The brainstem contains a region that regulates temperature, and laying a cold towel on the neck sends information straight there. The brainstem reads the interior as cold and works to raise temperature further. For that reason I do not recommend a cold towel on the neck.
Instead, applying ice water or cold water to the palms, the soles of the feet, or the forehead brings temperature down. These are hairless areas, and the blood vessels there have a particular structure. Cooling them directly cools the blood itself.
That said, the generally recommended first aid for heat illness is to cool the neck, the armpits, and the groin. What I have written above concerns the efficiency of lowering temperature. If you become unwell, please use the standard methods.
Conclusion
This piece has taken up water and salt, centred on habits that can be brought into daily life.
Water alone does not stay in the body. Salt is needed. And the question of how much draws different answers depending on where the answer comes from.
There is a great deal that improving daily habits can do. But rather than applying the numbers as given, it comes down to checking against your own body.
Next time, how the body is used through the day — alertness and metabolism.
Organizing the Body Through Daily Habits (Three Parts)
- Part 1: The Body Has a Clock — Light and Food Set the Day
- Part 2: Water Does Not Stay Without Salt — On Taking Things In (this article)
- Part 3: Focus and Fat-Burning Both Start in the Nervous System — Using the Day
Note, September 2026
The pieces behind this one were written in late June and July of 2023. Water and salt.
In the note to Part 1, I wrote about Attia’s four pillars — exercise, sleep, nutrition, and emotional health. Reading back, I noticed that water and salt appear in none of the four.
What the nutrition pillar covers is what you eat and how much, how blood sugar moves, whether protein is adequate. How much water to drink, how much salt to take, does not enter that frame.
I wrote this piece anyway because it is what gets asked in sessions. As I said at the start, the question arrives as: how should I improve my daily habits? And water comes up often.
What comes down from the frame and what comes up from the room are not the same.
In the body of the piece, I set out how the advice differs from person to person, for water and for salt alike. A researcher gives the mechanism, a trainer gives the number, a physician limits who it applies to. Three people saying different things within one territory.
That, I think, is part of what it means for something not to be in the frame. It was not the kind of question with a settled answer waiting to be fetched.