Why Does Salt Stop Diarrhea? The Science of Oral Rehydration

December 28, 2025 •

4 min read

The World Health Organization (WHO) has credited oral rehydration solutions (ORS) with saving millions of lives from dehydration caused by diarrhea. Understanding why does salt stop diarrhea involves delving into the ingenious physiological process that enables the body to absorb water and essential electrolytes, even during illness.

Quick Summary

Salt, combined with glucose in an oral rehydration solution (ORS), works through a critical sodium-glucose cotransport system to replace fluids and electrolytes lost during diarrhea, combating dehydration effectively.

Key Points

Sodium-Glucose Cotransport: Salt (sodium) and sugar (glucose) are absorbed together by special proteins in the small intestine, and water follows them into the bloodstream.
Dehydration Prevention: The absorption of salt and water prevents and reverses the life-threatening dehydration and electrolyte imbalance caused by diarrhea.
ORS Formulation: Oral Rehydration Solution (ORS) is a specific formulation of water, salt, and sugar designed to optimize fluid absorption, unlike plain water or sugary drinks.
WHO Recognition: Oral Rehydration Therapy (ORT), based on the sodium-glucose mechanism, is recognized by the World Health Organization and has saved millions of lives.
Correct Balance is Key: The right ratio of salt to sugar is essential for the system to work correctly and safely; an imbalance can be ineffective or harmful.

The Dehydration Problem in Diarrhea

Diarrhea, often caused by an infection of the intestines, leads to a rapid and significant loss of body fluids and electrolytes. In a healthy digestive system, the large intestine reabsorbs most of the water and sodium that pass through it. During a diarrheal illness, this reabsorption process is interrupted as the body rushes to expel the irritant, resulting in watery stools. This fluid loss can quickly lead to dehydration, which is particularly dangerous for infants, young children, and older adults.

Electrolytes, such as sodium, potassium, and chloride, are minerals that are vital for maintaining the balance of fluids in the body and for proper nerve and muscle function. When these are lost along with water, it can lead to severe electrolyte imbalances and other life-threatening complications if left untreated.

The Mechanism: Sodium-Glucose Cotransport

The key to understanding why salt helps with diarrhea lies in a unique physiological process within the small intestine known as the sodium-glucose cotransport system. This system, which remains intact even during most diarrheal illnesses, is the scientific basis for Oral Rehydration Therapy (ORT).

The Sodium-Glucose Partnership

Specialized proteins called SGLT1 (sodium-glucose cotransporter 1) are located in the walls of the small intestine. These proteins are responsible for actively transporting both sodium (from the salt) and glucose (from the sugar) from the intestinal lumen into the body's cells. Critically, this process works in a symbiotic way: the transport of sodium into the cell is dependent on the simultaneous transport of glucose. This perfect partnership ensures efficient absorption of both essential molecules.

The Osmotic Effect

When sodium and glucose are transported into the intestinal cells, they create an osmotic gradient. This means that the concentration of solutes inside the cells increases relative to the fluid outside. As a result, water is drawn passively across the cell membrane to maintain osmotic equilibrium, and follows the sodium and glucose into the body. This process is so effective that it can achieve rehydration even while diarrhea continues, effectively stopping the cycle of fluid loss.

What is an Oral Rehydration Solution (ORS)?

An Oral Rehydration Solution (ORS) is a precise mixture of water, salt (sodium chloride), and sugar (glucose or a similar carbohydrate) that leverages the sodium-glucose cotransport system to maximize fluid absorption. Developed and promoted by the WHO and UNICEF, ORS has become a cornerstone of global public health.

The Right Balance is Crucial

For the cotransport system to work optimally, the concentration of sodium and glucose must be carefully balanced. Standard sports drinks, for example, are generally not suitable for treating diarrhea because they contain too much sugar and too little sodium, which can actually worsen fluid loss.

Here are the standard components of an Oral Rehydration Solution:

Clean Water: The base fluid for rehydration.
Salt (Sodium Chloride): Provides the essential sodium electrolyte.
Sugar (Glucose/Dextrose): Helps facilitate the absorption of sodium and water.
Other Electrolytes: Depending on the formula, potassium and citrate may be included to prevent other imbalances.

ORS vs. Other Fluids for Diarrhea


Fluid Type	Suitability for Diarrhea	Advantages	Disadvantages
Commercial ORS	Ideal	Scientifically balanced ratio of electrolytes and glucose for maximum absorption.	May be less palatable to some.
Sports Drinks	Poor	Replenishes some electrolytes.	Too much sugar can worsen diarrhea; improper electrolyte balance.
Plain Water	Fair	Replaces lost fluid volume.	Does not replace lost electrolytes (sodium, potassium); can cause dangerous electrolyte imbalance.
Clear Broth	Good	Provides some sodium and fluid.	Lacks the precise glucose-sodium balance of ORS.
Homemade ORS	Good (if precise)	Can be made with common household ingredients (salt, sugar, clean water).	Requires accurate measurement to avoid potential side effects like sodium overload.

How to Use an Oral Rehydration Solution

For mild to moderate dehydration, ORS can be administered orally at home. The approach depends on age and severity:

For Adults and Older Children: Drink at least one cup of ORS for every loose bowel movement. Sip slowly to avoid vomiting.
For Infants and Young Children: Use a commercial ORS recommended by a pediatrician, as children are more vulnerable to dehydration. Breastfeeding should be continued alongside ORS administration.
Administration Method: ORS is typically consumed orally. In cases of persistent vomiting, small sips can be taken every few minutes. In more severe cases where a person cannot drink, medical professionals may use a nasogastric tube or intravenous fluids.

Conclusion

In summary, the reason why salt stops diarrhea is not that it halts the physical act of passing stool but that it enables the body to continue absorbing crucial fluids and electrolytes, preventing the dangerous side effects of dehydration. The simple yet brilliant combination of salt and sugar in Oral Rehydration Solutions (ORS) harnesses the small intestine's natural sodium-glucose cotransport system to restore balance. This mechanism has made ORT a life-saving therapy worldwide. When dealing with diarrhea, the strategic use of an appropriately balanced ORS is far more effective and safer than relying on plain water or sugary sports drinks to maintain hydration and promote recovery.

The Risks of Imbalance

It is vital to note that simply consuming excessive amounts of salt is dangerous and can lead to salt toxicity (hypernatremia). The proper balance found in commercially available or carefully prepared homemade ORS is what makes this treatment safe and effective. The Centers for Disease Control and Prevention provides comprehensive resources on treating diarrheal diseases, emphasizing the importance of proper rehydration strategies.

Frequently Asked Questions

No, plain salt water is not effective and can be dangerous. It lacks the glucose necessary for the sodium-glucose cotransport system to work and can cause salt toxicity or further dehydration if the concentration is incorrect.

Sugar (glucose) is a key ingredient because it is required for the intestinal cells to absorb sodium. This dual action, known as sodium-glucose cotransport, draws water into the bloodstream and helps rehydrate the body more efficiently than water alone.

Sports drinks are generally not recommended for treating diarrhea. They often have too much sugar, which can worsen diarrhea, and an incorrect balance of electrolytes for proper rehydration.

While commercial preparations are safer, a homemade solution can be made using one liter of boiled and cooled water, half a teaspoon of salt, and six level teaspoons of sugar. It is crucial to measure ingredients precisely to avoid complications.

Using too much salt can lead to hypernatremia, a dangerous condition caused by an excess of sodium in the blood. This can cause symptoms like weakness, confusion, severe thirst, and can lead to kidney damage.

For adults and older children, drinking at least one cup of ORS for every loose bowel movement is a good guideline. Dosage for infants and young children should be guided by a doctor and administered in small sips.

You should seek medical attention if you experience signs of severe dehydration, such as dizziness, dark urine, persistent fatigue, rapid breathing, or low blood pressure. Infants and young children are especially at risk and should be seen by a doctor if dehydration is a concern.

No, salt does not stop the actual flow of diarrhea. Its function is to help the body absorb the fluids and electrolytes that are being lost, thus preventing and treating dehydration, which is the primary danger associated with diarrhea.