Most people believe that coffee provides health benefits to moderate drinkers. The truth is, coffee and caffeine have a very small positive influence on health, and can have a wide range of negative effects. Aside from inducing brain fog, fatigue, depression and irritability, they can damage the digestive system and, through various mechanisms, bring on abdominal pain.
Coffee is renowned for its energizing effects as a high-yield source of caffeine, the only unregulated psychoactive drug. One of the means by which caffeine raises alertness is by elevating the stress hormones--cortisol, epinephrine and norepinephrine--increasing blood flow to the brain and muscles and raising heart rate. Unfortunately, this can be the very means by which susceptible individuals are caused to experience gastrointestinal discomfort.
This stressed state causes blood to be shunted to various systems in the body. The loser in this scenario is the digestive system, which is left running on minimal resources, which can, in itself, cause indigestion. Coffee also accelerates the secretion of gastric acids, speeding up the rate at which the stomach empties itself into the intestines. This can lead to highly acidic stomach contents being dropped into the intestine too soon, which can cause intestinal damage and, obviously, no small amount of abdominal discomfort. Coffee also has a laxative effect. Laxatives can cause intestinal spasm and hence pain.
Coffee can have numerous other negative effects on the digestive system, which may or may not lead to intestinal pain. These include decreasing absorption of magnesium, an element crucial for general health and maintaining bowel regularity. It can also act as a diuretic, leading to constipation, and interfere with the metabolism of GABA, an essential neurotransmitter that functions to calm the gastrointestinal tract. When GABA is in short supply, upset stomachs can become a regular event.
Some believe that by switching to decaffeinated coffee they'll neatly sidestep these problems. This is true of caffeine-specific effects but, unfortunately, many of coffee's pain-causing traits, such as its laxative effects, occur with decaf, too. Decaf is also just as acidic as regular coffee. Green tea, by contrast, while rich in caffeine, is far less likely to result in gastrointestinal discomfort.
If you experience abdominal pain after drinking coffee, you should first ascertain that it's coffee that's causing the pain, and not your milk or sweetener--lactose, fructose and sorbitol intolerance are common amongst Americans. If coffee is the cause then, short of taking an antacid tablet with every cup, the only cure is to quit. If you're a regular coffee drinker, however, cutting out caffeine cold turkey, as with any psychoactive drug, can bring on unpleasant side effects, causing you to "experience lethargy, depression, severe headaches, nausea, and even muscle and joint pain," according to Andrew Gaeddert in "Healing Digestive Disorders." He advises cutting out caffeinated sodas first, then gradually cutting your coffee with increasing amounts of decaf, and finally switching to a non-caffeinated tea such as rooibos or honeybush.