If you have never taken MCTs or Exogenous Ketones then it is possible that your body may respond with upset stomach or other digestive issues.
For MCTs this can be due to the rapid absorption of the fats. For Exogenous Ketones it may be because of the mineral that come along with these supplements or due to the lack of appropriate gut bacteria needed to manage ketone intake.
If you are new to taking these supplements, start with a ¼ to ½ serving and assess your tolerance before increasing to full servings. Over time your body will adjust to these supplements and you will be able to consume them in full serving amounts without a problem.