What Does Monosodium Phosphate Do to Your Body? A Complete Health Guide

November 25, 2025 •

4 min read

Approximately 85% of the body's phosphate is stored in the bones, but dietary intake, including forms like monosodium phosphate, can have complex effects on the body beyond basic nutrition. From its function as a food additive to its use in medical procedures, understanding what monosodium phosphate does to your body is crucial for managing your health and diet.

Quick Summary

Monosodium phosphate is a source of essential phosphorus used as a food additive and a medical laxative. While generally safe in moderation, excessive intake, particularly from processed foods, can lead to kidney issues, electrolyte imbalances, and negatively affect bone health.

Key Points

Essential Mineral Source: As a type of sodium phosphate, it provides phosphorus, a vital mineral for bone health, energy production (ATP), and cellular functions.
Food Additive: It is widely used in processed foods (labeled as E339i) as a buffering agent, stabilizer, and leavening agent, found in baked goods, meats, cheeses, and soft drinks.
Medical Laxative: Medically, it is utilized as a saline laxative to cleanse the bowel, pulling water into the intestines to facilitate a bowel movement.
High Bioavailability: Phosphate from additives like monosodium phosphate is almost completely absorbed by the body, whereas phosphate from natural food sources is less bioavailable.
Kidney Strain: Excessive phosphate intake, particularly from additives, can put a strain on the kidneys and lead to hyperphosphatemia, especially dangerous for those with compromised kidney function.
Bone Health Risk: A high phosphate-to-calcium ratio in the body can lead to calcium being leached from bones, weakening them and increasing the risk of cardiovascular calcification.
Electrolyte Imbalance: Overuse of sodium phosphate laxatives can cause severe dehydration and dangerous electrolyte imbalances, including seizures and heart problems in extreme cases.
Dietary Vigilance: Consumers of processed and packaged foods should be mindful of their total phosphate intake from additives, as it can significantly contribute to overall levels.

What is Monosodium Phosphate?

Monosodium phosphate (MSP), also known as sodium dihydrogen phosphate, is a chemical compound and a type of sodium salt of phosphoric acid. In the body, it serves as a crucial source of phosphorus, a vital mineral for numerous physiological processes. Beyond its role as a nutrient, MSP has widespread applications in the food industry, where it acts as a multifunctional ingredient. For example, it is used as a buffering agent to regulate acidity, a leavening agent in baked goods, and a stabilizer in dairy, meat, and fish products. It is officially designated as a food additive with the European number E339(i) and is generally recognized as safe (GRAS) by the FDA in controlled amounts.

The Body's Utilization of Phosphate

When monosodium phosphate is consumed, it dissociates in the gut, and the body absorbs the phosphate ions. This absorbed phosphate then enters the body's mineral metabolism pathway. Phosphate is the second-most plentiful mineral in the human body, with the majority concentrated in the bones and teeth. The body regulates its phosphate levels through a complex interplay between the kidneys, intestines, and bones, involving hormones like parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23).

Key functions of phosphate in the body:

Bone and Teeth Formation: Combining with calcium to form hydroxyapatite, which provides structural integrity to the skeleton.
Energy Production: Serving as a component of adenosine triphosphate (ATP), the primary energy currency of the cells.
Cellular Function: Acting as a building block for cell membranes, DNA, and RNA.
Acid-Base Balance: Acting as a buffering agent in blood to help maintain stable pH levels.
Neuromuscular Signaling: Aiding in proper nerve and muscle function.

Impact of Dietary and Additive Phosphate

The source of phosphate is a critical factor in how the body processes it. Natural, organic phosphate found in protein-rich foods like meat and dairy is absorbed less efficiently (60-80% bioavailability). In contrast, inorganic phosphate additives like monosodium phosphate, commonly found in processed foods, are almost 100% bioavailable. The rising use of these additives means that many people, particularly in Western countries, consume significantly more phosphate than their bodies require. Excessive intake of this highly absorbable form is where health risks begin to emerge, as the body's natural regulatory mechanisms can become overwhelmed.

Potential Health Effects of Excessive Intake

Kidney Function Impairment

For individuals with normal kidney function, the kidneys are highly effective at filtering out excess phosphate from the blood. However, this process becomes less efficient when kidneys are already compromised, as in chronic kidney disease (CKD). High phosphate levels (hyperphosphatemia) can build up, accelerating kidney damage and leading to a cascade of other health problems. The FDA has also warned that exceeding the recommended dose of over-the-counter sodium phosphate laxatives can lead to acute kidney injury, even in healthy individuals.

Adverse Effects on Bone Health

The body tightly controls the balance between calcium and phosphate. When blood phosphate levels get too high, it can disrupt this balance, causing the body to pull calcium from the bones to compensate. This can weaken the bones over time and increase the risk of conditions like osteoporosis. Furthermore, the excess calcium and phosphate can form deposits in soft tissues and blood vessels, a process known as vascular calcification, which increases the risk of heart disease.

Electrolyte Imbalance and GI Distress

Consuming high levels of sodium phosphate, particularly from laxative use, can cause severe dehydration and disrupt the balance of electrolytes in the body, such as calcium, sodium, and magnesium. This can result in serious complications affecting the heart and nerves, with reported side effects including seizures and arrhythmia in severe cases. Less severe, but more common, side effects include gastrointestinal issues such as stomach pain, nausea, bloating, and diarrhea.

Monosodium Phosphate as a Laxative

In a medical context, monosodium phosphate is used as a saline laxative for treating occasional constipation or as a bowel-cleansing agent prior to procedures like colonoscopies. Its mechanism is to increase fluid in the small intestine via osmosis, softening the stool and triggering a bowel movement. Due to the risks associated with high phosphate levels, oral sodium phosphate laxatives have been largely discontinued or are now available by prescription only in the U.S.. Strict adherence to dosage instructions and ensuring adequate hydration is critical to prevent dangerous side effects.

Food Sources: Natural vs. Additive Phosphate


Feature	Natural Phosphate	Additive Phosphate (e.g., from MSP)
Primary Source	Protein-rich foods like meat, dairy, nuts, and legumes.	Processed and packaged foods, sodas, fast food.
Chemical Form	Organic phosphate, complexed with proteins and other nutrients.	Inorganic phosphate, free and readily available for absorption.
Absorption Rate	Absorbed less efficiently (60-80%) in the intestine.	Almost completely absorbed (near 100%).
Risk of Excess	Lower risk of excessive intake due to lower bioavailability.	Higher risk of high blood phosphate levels due to high bioavailability.
Common Foods	Milk, cheese, egg yolks, fish, poultry.	Cured meats (ham, bacon), processed cheeses, baked goods, carbonated beverages.

Conclusion

Monosodium phosphate plays a dual role in the human body. As a controlled supplement or component of a balanced diet, it provides essential phosphorus necessary for strong bones, energy production, and cellular health. However, as a pervasive additive in processed foods, it contributes to an increasing and often unrecognized intake of inorganic phosphate. The high bioavailability of this additive form can disrupt the body's delicate mineral balance, posing significant health risks, especially to kidney and bone health, and potentially leading to electrolyte imbalances. While moderate intake is considered safe for most healthy individuals, reliance on highly processed foods necessitates awareness of total phosphate consumption. It is always wise for individuals with pre-existing conditions, particularly kidney issues, to monitor their intake carefully and consult a healthcare provider for personalized dietary advice. For more information on phosphorus intake, consult the National Institutes of Health Office of Dietary Supplements.

Frequently Asked Questions

Yes, monosodium phosphate is generally considered safe (GRAS) by food safety authorities like the FDA when consumed in moderate, regulated amounts within processed foods. However, excessive intake, particularly from processed food additives, can pose health risks over time.

Monosodium phosphate is used in many processed foods, including cured meats (like ham), processed cheeses, certain baked goods, evaporated milk, and some soft drinks.

For individuals with chronic kidney disease (CKD), the kidneys cannot efficiently filter excess phosphate. High intake of monosodium phosphate can lead to elevated blood phosphate levels (hyperphosphatemia), accelerating kidney damage and potentially causing bone and cardiovascular problems.

Yes. When used as a saline laxative for medical purposes, monosodium phosphate works by drawing water into the intestine, which effectively softens stool and induces a bowel movement.

Monosodium phosphate and MSG (monosodium glutamate) are completely different chemical compounds. Monosodium phosphate is a salt of phosphoric acid and provides phosphorus, while MSG is a salt of glutamic acid used as a flavor enhancer.

Additive phosphate is considered more readily and completely absorbed by the body than natural phosphate from whole foods. This higher bioavailability means that a diet high in processed foods can cause a greater increase in blood phosphate levels, posing a higher risk.

While difficult to detect in early stages, signs of hyperphosphatemia can include symptoms of electrolyte imbalance like nausea, muscle cramps, lethargy, and in severe cases, seizures or heart rhythm abnormalities.