# Why Do Chinese People Say "Body Fluids Deficiency" (jin ye bu zu)? Your Body Isn't Thirsty—It's Running Low on Lubricant and Coolant
A Question
Have you ever had this experience?
You wake up in the morning with a mouth so dry it feels like you've been chewing cotton all night. You get up and gulp down a glass of cool boiled water, your throat feels a little better, and half an hour later it's dry again. It's not thirst—it's "not getting moistened."
Sitting in an air-conditioned room staring at your computer, your eyes get increasingly dry. You put in eye drops, they help for five minutes, then they're dry again. It's not sleepiness—it's "your eyes are out of oil."
After playing ball in the summer, you sweat buckets and feel dizzy and lightheaded. You drink a bottle of iced cola, but you still don't feel refreshed. It's not the heat—it's "coolant loss."
As people get older, they wake up in the morning with knees that click and crack. Squatting down and standing up, the joints feel like rusty hinges. It's not old age—it's "not enough lubricating oil."
You go to the hospital, get your blood sugar checked, thyroid function checked, kidney function checked. The doctor says: "All your numbers are normal. Drink more water and get some rest."
You go see a TCM doctor. The old man takes one look at your tongue and says: "Body fluids deficiency (jin ye bu zu)."
You've drunk water until your stomach is bloated, and you're still deficient in body fluids? What exactly are these body fluids, and how are they different from water?
Even more absurd is that Chinese people use the same word to praise someone: "This person has ample body fluids, great complexion"; or to describe a place as livable: "This place has abundant body fluids, nurturing great talents." The same word, sometimes describing the body, sometimes describing feng shui. What is this thing?
Traditional Chinese Explanation
"Jin" and "ye" (津 and 液) are actually two different things in TCM, but for everyday understanding, you only need to remember one metaphor: they are both "water" in the body, but not the water you drink—they are water that the body has processed itself, useful water.
TCM divides body fluids into several categories, but in daily life, you only need to remember four kinds of "liquid":
Saliva (kou ye) — oral lubricant. Speaking, eating, swallowing—all depend on it. People with ample saliva have moist lips, speak fluently, and enjoy every meal. People with insufficient saliva have dry mouth, bad breath, speak with a hitch, and need soup to wash down dry rice. Saliva is like the lubricant in your mouth; without it, the machine can't turn.
Tear fluid (lei ye) — eye washing fluid. Protects the eyeball, lubricates the cornea, and flushes away dust. People with ample tear fluid have bright, spirited eyes, and don't tear up even in strong wind. People with insufficient tear fluid have dry, itchy, red eyes; after half an hour looking at a screen they can barely open them, and the wind makes tears stream down. Tear fluid is like the windshield washer fluid for your eyes; without it, vision is blurred, and the glass gets scratched.
Sweat (han ye) — body coolant. Dissipates heat, expels waste, and regulates body temperature. People with normal sweat function perspire during exercise, feel clear and open, and tolerate summer heat. People with sweat dysfunction either sweat without moving (spontaneous sweating), or don't sweat when hot (anhidrosis), or feel dizzy and weak after sweating (depletion). Sweat is like the coolant in a car; when circulation is normal, the engine doesn't overheat; when circulation fails, either the radiator boils over or the system freezes.
Joint fluid (guan jie ye) — bearing lubricant. Keeps joints flexible, cushions pressure, and reduces friction. People with ample joint fluid squat and rise with ease, and walk with a spring in their step. People with insufficient joint fluid have knees that click, pain going up and down stairs, and can't squat down or stand up. Joint fluid is like the lubricant in machine bearings; enough oil, and it turns smoothly; not enough oil, and it grinds dry until it breaks.
These four liquids together constitute what TCM calls "body fluids (jin ye)." It is not one specific substance, but the sum total of all the body's lubrication and cooling systems—secretion, circulation, regulation, and protection, all included.
The ancients were very smart. They discovered that there is a kind of "self-processed water" in the body that keeps things running. When it is abundant, your eyes are bright, your mouth is moist, your skin is smooth, and your joints are flexible. When it is insufficient, the whole body is dry, stuck, and rusty. They didn't know how to name it, so they used the simplest word: "body fluids (jin ye)"—jin, a ferry crossing, extended to mean circulating liquid; ye, something that can flow and has a moistening effect.
Coach Liu's Modern Translation
Alright, now let me translate "body fluids" into modern terms.
I'm not going to talk about extracellular fluid, interstitial fluid, mucosal secretion, or synovial fluid. Too complicated. You just need to remember one metaphor:
Your body fluids are your body's lubricant and coolant system.
It's that simple. Your "body fluids" are essentially functional liquids that the body produces and distributes itself. But they are not tap water—you can't just pour them in and be done.
Specifically:
What does saliva correspond to? It corresponds to your oral mucosa's "active secretion capacity." Drooling when you see delicious food isn't greed—it's your body pre-secreting lubricant in preparation for digestion. If salivary gland function declines, no matter how much water you drink, your mouth will still be dry, because water isn't saliva—saliva contains digestive enzymes, antimicrobial proteins, and mucins, a "high-grade liquid" processed by the body.
What does tear fluid correspond to? It corresponds to your lacrimal glands' "homeostatic secretion capacity." Tear fluid isn't only there when you cry; it's secreted every minute, just in small amounts you can't see. Staring at a screen without blinking, tear film evaporates too quickly, and the lacrimal glands get exhausted. Eye drops only provide temporary relief, because they are external, not the body's own formula.
What does sweat correspond to? It corresponds to your body's "temperature regulation system." Sweating isn't just about draining water; it drains metabolic waste (urea, salts, lactic acid) while carrying away heat. After heavy exercise, what you lose isn't just water, but also electrolytes and energy. Drinking only water without replacing electrolytes makes the body weaker and weaker.
What does joint fluid correspond to? It corresponds to your synovial membrane's "lubrication and cushioning capacity." Joint fluid isn't stagnant water; it circulates and renews as the joint moves, providing nutrients to the cartilage. Sitting still for long periods, joint fluid doesn't circulate, like lubricant that has settled, and the joint naturally rusts. Conversely, excessive exercise squeezes joint fluid out, and cartilage rubs directly against bone, which is also prone to wear.
So, "body fluids deficiency" is not "not drinking enough water." It means: the body's capacity to produce, distribute, and circulate these functional liquids has declined.
The ancients didn't have microscopes, but they used the concept of "body fluids" to precisely describe what modern people need four concepts to explain: "mucosal secretion function," "tear film stability," "temperature regulation efficiency," and "joint synovial fluid circulation."
Real-Life Examples
Four anecdotes to help you instantly understand what "body fluids" are.
Example One: Dry mouth that drinking water doesn't fix.
You stay up until two in the morning, and the next day you wake up with a mouth dry like the desert. You gulp down two large cups of warm water, your throat feels a little better, and half an hour later it's dry again. You think it's "internal heat," so you brew chrysanthemum tea, drink mung bean soup, but it's still dry.
TCM says: "Body fluids deficiency." You don't understand: I clearly drank a stomach full of water, how can I still be deficient?
The truth: Staying up late damages yin, and the body's "liquid processing factory" has shut down. Water goes in, isn't processed into saliva, mucosal fluid, or interstitial fluid, and is directly turned into urine and expelled. You drank water, but what the body wants is "processed liquid." Raw materials are piled in the warehouse, but the production line isn't turning, and the product is still short.
Example Two: Dry, itchy eyes; eye drops make them drier.
You stare at a screen in an air-conditioned room for ten hours every day, your eyes dry like the Sahara. You put in eye drops from Japan, cool and stimulating, they help for five minutes, then they're dry again. You switch to several kinds of eye drops, becoming more and more dependent.
TCM says: "The liver opens into the eyes; body fluids cannot ascend to moisten." You don't understand: what does this have to do with the liver?
The truth: Tear secretion is an active regulatory process. Long-term screen staring reduces blink frequency from 20 times per minute to 5 times, tear film evaporates too quickly, and the lacrimal glands are worn out. The preservatives in eye drops also damage corneal cells, making them drier the more you use them. This isn't a problem of lacking water; it's the "tear production system" on strike. Resting your eyes, warm compresses, and promoting natural secretion are more effective than eye drops.
Example Three: Heavy sweating after exercise, dizziness and weakness.
You go running in the summer, five kilometers down, your clothes can be wrung out. You go home and drink two bottles of ice water, lie down to rest, and end up dizzy, nauseous, and weak in your hands and feet. You think it's "heat stroke," but your body temperature is normal.
TCM says: "Excessive sweating, body fluids leaking outward, qi follows fluids and escapes." You don't understand: isn't sweating detoxification? How can it detoxify you into weakness?
The truth: Sweat isn't pure water; it contains sodium, potassium, chloride, and glucose. After heavy sweating, drinking only pure water dilutes the electrolytes in your blood, actually worsening electrolyte imbalance. Dizziness and weakness are because "coolant" has been lost in excess, and the body enters a protective low-power mode. The correct approach is to drink lightly salted water or sports drinks to replenish electrolytes.
Example Four: Clicking joints, can't squat down.
You're in your thirties, and when you get up in the morning, your knees click. You squat down to tie your shoelaces, you have to hold the wall. You think it's "calcium deficiency," so you take calcium supplements for half a year, but they still click. You get an X-ray, and the doctor says "bones are fine, might be cartilage wear."
TCM says: "Body fluids cannot moisten; joints lose nourishment." You don't understand: what does cartilage have to do with body fluids?
The truth: Joint cartilage has no blood vessels; its nutrition entirely depends on joint fluid for transport. Insufficient or poorly circulating joint fluid means cartilage can't get nourishment, like machine bearings lacking oil, grinding dry. Long-term dry grinding thins the cartilage until it wears out. Calcium supplements bones, not joint fluid. Moderate exercise promotes joint fluid circulation—that's the real way to "add lubricating oil."
Four examples, one underlying logic: the body's efficiency in producing and using functional liquids has a problem.
Modern Research
Is there scientific research on "body fluids"?
Yes, but scientists don't use the word "body fluids." They use:
• Mucosal secretion function. Research has found that people who stay up late for long periods or are under stress have salivary gland secretion reduced by more than 30%, and the immunoglobulin A (IgA) content in saliva also decreases. This is the modern medical manifestation of "saliva deficiency"—it's not that you didn't drink water, but that gland function is suppressed.
• Tear film stability. Ophthalmology research has found that video display terminal (VDT) syndrome patients have significantly shortened tear film breakup time and decreased tear secretion. This is the scientific version of "tear fluid deficiency"—it's not that the eyes lack water, but that the lacrimal glands' homeostatic secretion has been disrupted.
• Temperature regulation and electrolyte balance. Sports medicine research has found that after heavy sweating, if only pure water is supplemented, it can lead to hyponatremia, resulting in dizziness, nausea, and even confusion. This is the scientific explanation of "sweating damages body fluids"—what's lost isn't water, but functional liquids containing electrolytes.
• Joint synovial fluid composition. Research has found that joint synovial fluid contains hyaluronic acid, glucosamine, and chondroitin, which decrease with age. People who sit still for long periods have poor synovial fluid circulation and insufficient cartilage nutrient supply. This is the microscopic mechanism of "joint fluid deficiency"—it's not that bones lack calcium, but that the lubrication and nutrient delivery system has declined in efficiency.
There isn't much of this research, but the direction is consistent: "body fluids" describes the body's overall state of producing, distributing, and circulating functional liquids, not one specific substance, nor simply "not drinking enough water."
Practical Methods
Now that you understand "body fluids," how do you replenish them?
First, let's dispel a few misconceptions:
• Gulping water can't replenish body fluids. Water is from nature; body fluids are processed by the body. Drinking too much water increases the burden on the kidneys, and instead expels more electrolytes. People with body fluids deficiency aren't drinking too little; it's the body's capacity to process liquids that has declined. Gulping is ineffective; small, slow sips are useful.
• Eye drops can't replace tear fluid. Artificial tears can only temporarily moisten; they can't repair lacrimal gland function. Long-term dependence damages corneal cells, making them drier the more you use them. Letting your eyes rest, warm compresses, and promoting natural secretion are the fundamentals.
• Calcium supplements can't replace joint fluid. Calcium supplements bone hardness and nerve conduction; joint fluid is secreted by the synovial membrane, and the composition is completely different. Calcium supplements are basically useless for clicking joints; moderate exercise promoting synovial fluid circulation is the real solution.
Specific methods:
• Small, slow sips. Not gulping, but small, frequent, warm sips. Each time 100-150 ml, giving the digestive system time to absorb and transform. Ice water stimulates the stomach and intestines, reducing absorption efficiency. Warm water is the most nourishing—this is what the ancients meant by "warmly nourishing body fluids."
• Eat juicy foods. Pears, watermelon, white fungus (tremella), lily bulbs, lotus root—the "juice" in these foods is more easily transformed by the body into body fluids. It's not about eating fruit until you're full, but prioritizing foods rich in water and easy to digest, reducing the burden on the digestive system, and saving energy to produce body fluids.
• Moderate exercise. Walking, swimming, tai chi—these low-intensity exercises promote the circulation of liquids throughout the body, including joint fluid, interstitial fluid, and lymphatic fluid. Sedentary people have stagnant liquid circulation, like a stagnant pond that easily becomes foul. Get moving, and body fluids can "come alive."
• Don't stay up late. This is the most important point. From 11 p.m. to 3 a.m. is the body's key time for repairing and generating body fluids. Staying up late means making the "liquid processing factory" work the night shift without overtime pay. Short term, it's fine; long term, body fluids will definitely be depleted.
• Humidify your indoor environment. Air-conditioned rooms, heated rooms, with air humidity below 30%, accelerate the evaporation of body fluids from the skin, eyes, and respiratory tract. This isn't your body's problem; it's the environment stealing your body fluids. Run a humidifier to 50-60% humidity, reduce unnecessary evaporation, and help your body save some oil.
You don't need to believe in TCM to use these methods. You just need to understand: your body is not a bucket that fills up when you pour water in. Your body is a complex liquid processing factory—raw materials need to be processed, products need to be distributed, and circulation needs to be unobstructed. You are taking care of the entire system, not a single indicator.
One-Minute Summary
🕐 One Minute to Understand "Body Fluids"
Body fluids (jin ye) = The body's lubricant and coolant.
Saliva = Oral lubricant (essential for speaking and eating).
Tear fluid = Eye washing fluid (protects the eyeball).
Sweat = Body coolant (dissipates heat and expels waste).
Joint fluid = Bearing lubricant (keeps joints flexible).
Signs of body fluids deficiency: dry mouth, dry eyes, weakness after sweating, clicking joints—the whole body is dry, stuck, and rusty.
Causes: staying up late, sedentary lifestyle, gulping water, excessive eye use, dry air-conditioned rooms.
Methods: small slow sips, eat juicy foods, moderate exercise, don't stay up late, humidify indoors.
The ancients called it "body fluids (jin ye)"; modern people call it "functional liquid metabolism."
Different names, but the body knows: a machine without oil can't turn; a body without fluids is dry.
xiaokz · Concept 12
Using the language of modern science to help the world understand traditional Chinese wisdom.
Not mysterious, not superstitious, not dismissive.
Understand, rather than merely believe.