Coffee has been known to send a signal to the stomach to release gastrin, which triggers a wave of contractions in the intestine called peristalsis. This process helps move food and fluid through the intestines. Caffeine is a great energy stimulator, but it can also stimulate the urge to defecate. Studies have shown that it can activate contractions in the colon and intestinal muscles.
Coffee can make you poop regardless of its caffeine content, and decaffeinated coffee has the same laxative effect on some people. The communication between the stomach, brain and colon, known as the gastrocolic reflex, is a normal response to eating. But coffee seems to have a disproportionate effect; a study published in 1998 found that eight ounces of coffee stimulated colonic contractions similar to those induced by a 1,000-calorie meal. Researchers believe that this is caused by one or more of the many chemicals in coffee, and may be mediated by some of our own hormones that play an important role in the digestive process, such as gastrin or cholecystokinin. Caffeinated coffee may make people more eager to defecate than decaffeinated coffee. However, this study shows that when manufacturers eliminate caffeine from coffee, people may still feel like defecating after drinking decaffeinated coffee.
People with IBS and older adults may be more likely to suffer from IBS because their intestines are more sensitive to the effects of coffee. The general digestive effects of coffee, milk and the time you drink it can contribute to the laxative effect. While the mechanism is still unclear, the effects of coffee on the intestine may be helpful for some people, including those recovering from certain types of surgery. The urge could also hit you more suddenly, or it could be less time between drinking your cup of coffee and having to go. Coffee has been shown to improve liver health, decrease the risk of colon cancer, improve cognitive function, decrease the risk of cardiovascular death (CHF, heart attack, stroke), type II diabetes, Parkinson's, etc. So if coffee leads to the production of gastrin, leading to increased contractions of the colon, this is another way that coffee can provoke our breaks. Many people assume that coffee poops because it can contain a lot of caffeine depending on how the coffee beans are roasted.
Coffee contains thousands of compounds, but none has been definitively linked to the urge to defecate after drinking coffee. Some people find that coffee causes an upset stomach and loose stools, as well as side effects related to excess caffeine such as insomnia, anxiety, palpitations and headache. There is no specific amount of coffee that stimulates bowel movements because it is different for each person. But for the rest of us, coffee can be part of a comforting morning routine, waking us up in many ways.