Why Does Milk Cause Diarrhea While Formula Doesn't?

Why does drinking milk cause diarrhea, but drinking formula does not?

Why do I get diarrhea after drinking milk but not after consuming milk powder?

Habibi, 10~19 year old female. Ask Date: 2007/04/20

Dr. Shi Guimei reply Nutrition

Hello! Drinking fresh milk may cause diarrhea, while reconstituted milk powder does not.
There are several possible reasons for this: 1.
The fresh milk you selected is whole milk, which has a high fat content, whereas the milk powder you are using is low-fat or non-fat, resulting in a lower fat content.
2.
When reconstituting milk powder, the amount of powder used may be less or the amount of water may be more, leading to a lower concentration and consequently a lower osmotic pressure, which is less likely to cause diarrhea.
3.
If the milk powder you are using has a lower lactose content or is a special formula that is lactose-free, it can also reduce the incidence of diarrhea.
Sincerely, Dietitian Shih Kuei-Mei, Director of the Nutrition Department, Taoyuan Hospital, Ministry of Health and Welfare.

Reply Date: 2007/04/20

More Info

The question of why milk can cause diarrhea while formula does not is an interesting one and can be attributed to several factors related to the composition of the milk and the individual's digestive system.
Firstly, one of the most common reasons for this phenomenon is lactose intolerance. Lactose is the sugar found in milk, and many individuals, especially adults, have varying degrees of lactose intolerance. This means that their bodies do not produce enough lactase, the enzyme required to break down lactose into glucose and galactose for absorption. When lactose is not properly digested, it can lead to symptoms such as bloating, gas, and diarrhea.
In contrast, many infant formulas are either lactose-free or contain significantly lower levels of lactose compared to whole milk. Some formulas are designed specifically for lactose-intolerant infants, utilizing alternative carbohydrate sources like corn syrup solids or sucrose. Therefore, if a person is lactose intolerant, they may experience diarrhea after consuming regular milk but not after consuming formula.

Another factor to consider is the fat content of the milk. Whole milk contains a higher fat content compared to many formulas, which can also affect digestion. High-fat foods can sometimes slow gastric emptying, leading to discomfort and diarrhea in sensitive individuals. If the formula being consumed is lower in fat or has a different fat composition, it may be easier for some individuals to digest.

Additionally, the concentration of nutrients and the osmotic load of the liquid can play a role. When consuming milk, especially in larger quantities, the osmotic pressure can increase, leading to diarrhea as the body attempts to balance the concentration of solutes in the intestines. If the formula is diluted with more water or is consumed in smaller amounts, it may not exert the same osmotic effect, thus reducing the likelihood of diarrhea.

Moreover, the protein composition in milk versus formula can also be a contributing factor. Cow's milk contains a different protein structure compared to the proteins found in many infant formulas, which can sometimes lead to gastrointestinal distress in individuals who are sensitive to these proteins. Some people may have a sensitivity or allergy to the proteins in cow's milk, leading to symptoms that can include diarrhea, while they may tolerate the proteins in formula better.

In summary, the reasons why milk can cause diarrhea while formula does not can be attributed to lactose intolerance, differences in fat content, osmotic load, and protein composition. If someone experiences diarrhea after consuming milk but not after formula, it may be beneficial to consult with a healthcare provider to explore the possibility of lactose intolerance or other underlying digestive issues.
For those who are lactose intolerant, lactose-free milk or dairy alternatives such as almond milk, soy milk, or oat milk can be good substitutes. Additionally, if a child is not consuming milk due to digestive issues, exploring fortified plant-based milk options or lactose-free dairy products can help ensure they receive adequate nutrition without the adverse effects.

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