Why does drinking iced milk tea in summer easily cause diarrhoea?

As summer arrives, many people habitually buy a cup of iced milk tea to cool down. However, this refreshing sensation is often accompanied by abdominal cramping or diarrhea. Why does drinking iced milk tea in summer make diarrhea particularly likely?

Ice Cubes Are Easily Contaminated by Bacteria

Summer is the peak season for bacterial activity. If restaurants fail to rigorously control the hygiene of their water sources for ice-making or their storage processes, ice cubes are highly susceptible to contamination by E. coli. The most dangerous aspect is that sugary milk tea provides ample nutrients for bacteria. Once contaminated ice cubes are added, E. coli multiplies even faster. When you drink this seemingly refreshing milk tea, you are also consuming a large number of rapidly reproducing pathogens.

The Danger of Humid, Hot Environments

Many people habitually buy a cup of iced milk tea and then sip it intermittently throughout the day to make it last. In the hot, humid summer environment, if the drink is left at room temperature for extended periods without adequate refrigeration, bacteria enter a “rapid reproduction” phase. As the ice melts and the temperature rises, the number of bacteria in the cup grows exponentially, transforming a refreshing breakfast drink into a trigger for gastroenteritis.

Cold Stimulation Disrupts the Intestines

Beyond bacterial factors, physical stimulation should not be underestimated. After leaving high outdoor temperatures and entering an air-conditioned room, immediately drinking iced milk tea causes a strong cold stimulus. This leads to sudden constriction of gastrointestinal blood vessels and abnormally rapid peristalsis. This temperature shock disrupts the rhythm of the digestive system, triggering spasmodic abdominal pain or acute watery diarrhea.

The Impact of Lactose Intolerance

For individuals with lactose intolerance during the sensitive summer intestinal period, if the lactose in milk tea is not effectively broken down, it ferments and produces gas in the intestines. Additionally, the “theophylline” in the strong tea base promotes gastrointestinal motility. Together, these two factors accelerate the urge for bowel movements.

Drinking Iced Milk Tea for Breakfast: Nicknamed the “Strongest Laxative”

Taiwanese gastroenterologist and hepatologist Dr. Fan Chuan-shan explained on the program Health 2.0 that the laxative effect of drinking iced milk tea can be attributed to four main factors:

Consumption in the morning: Upon waking, the body’s organs are not yet fully alert and are more sensitive. Drinking iced milk tea in the morning can greatly stimulate the unprepared gastrointestinal tract, promoting bowel movements.
Large volume: A full cup of iced milk tea is a considerable volume. Drinking large amounts in the morning creates more waste, naturally prompting the need for elimination.
Low temperature: Food temperature affects gastric emptying. More stimulating temperatures, whether extremely cold or hot, have an impact. If the stomach empties without undergoing sufficient digestion, food is sent directly to the intestines. Iced milk tea stimulates this accelerated transport, leading to bowel movements or diarrhea.
Ingredients containing milk: Whether made with non-dairy creamer or fresh milk, both can stimulate bowel movements. Non-dairy creamer contains palm oil or olive oil, which irritate the intestinal wall; fresh milk may trigger lactose intolerance, leading to diarrhea.

Fan noted that for most people, drinking iced milk tea with breakfast can achieve a laxative effect and aid bowel movements, but it does not necessarily cause diarrhea.

3 Types of Constipation and Relief Recommendations

Nutritionist Li Wan-Ping once explained that constipation can be divided into three types:

Feeling the urge to defecate but being unable to do so.
Stools that are hard and pellet-like, with foul-smelling flatulence.
Stools with strong adhesion.

For these three types of constipation, adopting corresponding dietary and lifestyle approaches can help improve the condition.

When to Seek Medical Attention for Constipation

According to the Hong Kong Department of Health, constipation is a common issue. It refers to infrequent bowel movements (less than 3 times per week), with stool that is too hard, too small in size, or difficult to pass. Seek medical attention if constipation is accompanied by the following: