Coconut oil may upset your stomach for two reasons. One, when you drink it on an empty stomach. When nothing is there to slow the digestion of coconut oil, it quickly stimulates your intestinal muscles that triggers more contractions and relaxations.
These movements in turn cause the stool to release some gas. When gas is trapped in your intestines, you get stomach ache as a result. Coconut oil has the ability to soften stool too. When stool becomes soft, it releases gas as well. Which can upset your stomach even more and make you miserable.
The second reason is when you consume too much coconut oil even with food. This may cause nausea and make you feel like vomiting. The reason for such side effect from eating coconut oil is that your body has yet to adapt to coconut oil.
All you need to do to prevent stomach discomfort is to start off with a small amount of coconut oil added to meals. Increase your consumption of coconut oil gradually and progressively.