What Would Happen if I Only Drank Milk Instead of Water?

November 8, 2025 •

4 min read

An article published in the American Journal of Clinical Nutrition found that milk can actually be more hydrating than plain water due to its electrolytes, but what would happen if I only drank milk and completely cut out water? It's a question that raises serious health concerns and reveals why water is an irreplaceable component of our diet.

Quick Summary

This article explores the severe health consequences of exclusively drinking milk, which includes potential risks like nutritional deficiencies, kidney stress, excessive calorie intake, and digestive issues for lactose-intolerant individuals. It clarifies why milk cannot substitute for water despite its hydrating properties and nutritional content.

Key Points

Nutrient Deficiencies: An exclusive milk diet lacks essential nutrients like fiber, iron, and vitamin C, leading to issues like severe constipation, anemia, and scurvy over time.
Kidney Strain: The high levels of calcium, potassium, and phosphorus in large volumes of milk overwork the kidneys and can cause milk-alkali syndrome and chronic kidney disease.
Caloric Excess and Weight Gain: Replacing all fluid intake with milk, especially whole milk, dramatically increases daily calorie consumption, leading to unhealthy weight gain.
Digestive Distress: Even for non-lactose intolerant individuals, consuming large quantities of milk can cause bloating, gas, and diarrhea due to the high lactose and casein protein content.
Irreplaceable Function of Water: Water is essential for countless bodily functions, including flushing toxins and regulating temperature, which milk cannot replicate effectively due to its nutrient load.
Lactose Intolerance Exacerbation: For those with lactose intolerance, an exclusive milk diet would cause severe and constant digestive pain and discomfort.

The Core Problem: Nutritional Imbalance and Caloric Overload

While milk is a nutritious beverage, packed with protein, calcium, and vitamin D, it is not a complete food source for adults. Exclusive reliance on milk for all fluid intake introduces a profound nutritional imbalance and a dangerous caloric surplus. A person drinking the recommended daily fluid intake exclusively from milk, especially higher-fat varieties, would consume an excessive amount of calories, leading to significant and unhealthy weight gain. This caloric overload would disrupt a balanced dietary pattern, pushing out other essential food groups and their unique nutrients. The slow gastric emptying caused by milk's protein and fat content, while potentially beneficial for satiety in moderation, could lead to a constant feeling of fullness, further suppressing the appetite for solid foods.

Deficiencies Caused by a Milk-Only Diet

Despite its nutrient density, milk lacks several key components necessary for long-term human health. Replacing water with milk would inevitably lead to specific nutritional deficiencies over time.

Vitamin C: Milk contains negligible amounts of this crucial vitamin. Without fresh fruits and vegetables, a person would quickly face the risk of scurvy, a disease caused by severe vitamin C deficiency that impairs collagen synthesis.
Fiber: Milk contains no dietary fiber. Fiber is essential for digestive health, regulating bowel movements, and maintaining a healthy gut microbiome. A lack of fiber would lead to severe constipation and other gastrointestinal problems.
Iron: Milk is a poor source of iron, and its high calcium content can actually inhibit iron absorption. The resulting iron deficiency would cause anemia, characterized by fatigue, weakness, and impaired cognitive function.

The Strain on Kidneys from Excessive Intake

One of the most critical health risks of only drinking milk is the potential for kidney damage. Healthy kidneys are able to handle moderate milk consumption, and some research even suggests low-fat dairy may have a protective effect. However, in large quantities, milk becomes a burden. The high levels of calcium, potassium, and phosphorus found in milk force the kidneys to work overtime to filter these minerals from the blood.

Over time, this can lead to a condition known as milk-alkali syndrome, characterized by hypercalcemia (excess calcium in the blood), metabolic alkalosis, and potential kidney damage. In severe, chronic cases, milk-alkali syndrome can cause permanent kidney failure. For individuals with pre-existing kidney disease, milk consumption is already restricted, making a milk-only diet particularly dangerous. The body's need for pure water to flush out waste products and maintain proper kidney function is non-negotiable.

Digestive Distress and Intolerance

Consuming large, exclusive quantities of milk is a recipe for severe digestive problems. Even for those without a diagnosed lactose intolerance, the sheer volume of lactose—the natural sugar in milk—would likely overwhelm the digestive system. The enzyme lactase, which breaks down lactose, naturally decreases in production after infancy for many adults.

The digestive distress would manifest as bloating, gas, stomach cramps, and diarrhea as undigested lactose ferments in the large intestine. For individuals with casein sensitivity, a distinct issue from lactose intolerance, a diet of only milk could trigger inflammatory responses and lead to more serious symptoms like skin rashes, joint pain, and fatigue.

Water vs. Milk: A Comparison of Functions


Feature	Water	Milk (Cow's)
Primary Function	Hydration, metabolic functions, waste removal	Hydration, nutrition (protein, fat, vitamins, minerals)
Caloric Content	0 calories	High, varies with fat content (e.g., 147 kcal/cup whole milk)
Nutrient Balance	Pure, neutral medium	Rich in some nutrients, lacking others (fiber, iron, Vitamin C)
Impact on Kidneys	Supports healthy filtration and waste removal	High mineral content strains kidneys in excess
Digestive Impact	Facilitates digestion and softens stool	Can cause bloating, gas, and cramps due to lactose and protein
Long-Term Suitability	Essential and irreplaceable for life	Unsustainable and dangerous as a sole liquid source

Conclusion: A Perilous Path to Severe Health Problems

Drinking only milk in place of water is a dangerous and unsustainable proposition for any adult. While milk is a valuable part of a balanced diet, its nutrient profile is incomplete and its caloric density is too high to serve as a primary fluid source. The body relies on pure water to perform critical functions, including waste removal and maintaining a proper fluid balance. The resulting deficiencies of fiber, vitamin C, and iron, coupled with the potential for excessive calcium and phosphorus intake, would lead to severe health complications. From digestive distress and weight gain to kidney damage and nutrient deficiencies, the consequences of replacing water with milk are severe and life-threatening. For optimal health, a balanced diet paired with ample plain water remains the gold standard for hydration.

Frequently Asked Questions

While some studies suggest milk may hydrate more effectively than plain water in certain situations, like after intense exercise, it should not replace water entirely. The nutrient content that makes milk slightly more hydrating also makes it calorically dense and a poor substitute for daily, routine hydration.

A diet consisting only of milk is deficient in several critical nutrients, including dietary fiber, vitamin C, and iron. This can lead to severe issues like scurvy and anemia.

Yes, excessive milk consumption can be harmful to the kidneys, particularly due to its high potassium and phosphorus content. This can strain the kidneys and, in rare cases, lead to a dangerous condition called milk-alkali syndrome.

No, it is not possible for an adult to remain healthy long-term by drinking only milk. While it provides energy and some nutrients, it lacks others and causes dangerous imbalances.

Yes, exclusively drinking milk for all fluid needs can lead to significant weight gain. Milk contains calories, and consuming the volume needed for adequate hydration would result in a massive caloric surplus.

A milk-only diet would cause severe digestive issues, including constipation from lack of fiber, and bloating, gas, and diarrhea from the overwhelming lactose and protein content.

Milk-alkali syndrome is a serious condition caused by the excessive intake of calcium and alkali, which can be triggered by large quantities of milk. It leads to hypercalcemia, metabolic alkalosis, and potential kidney damage or failure.