If I get diarrhea after eating does that mean my body is not absorbing the calories or fat and vitamins?

Possibly. It might also mean you are sensitive to a particular food. If you're lactose intollerant, for example, you will getting bloating, gas and diarrhea after eating dairy. It's helpful to keep a food log and write down what you eat and when you have diarrhea. This will help you see what foods trigger the problem. If this has only been going on for a short time, it might be something viral.
Many causes. There are many causes of diarrhea after eating. It could even be related to your gallbladder. I suggest an appointment with your physician to figure out the possible causes and treatments.