Hello,
Thanks for your query.

I appreciate your efforts for medical consultation in so much distress.
Important aspects of your query are:
•     50 year old male
•     Healthy life style
•     History of consumption of high fat outside food followed by bowel symptoms

From your description it is clear that you are having symptom called as 'rectal tenesmus'.
Tenesmus is the feeling that you constantly need to pass stools, even though your bowels are already empty. It may involve straining, pain, and cramping.

Causes: There is plenty of cause of tenesmus. I would be mentioning only the relevant causes in following hierarchy:
•     Transient motility disorder: due to outside food intake
•     Irritable bowel syndrome
•     Lower GI parasitic infection, particularly Trichuris trichiura (whipworm)
•     Amebiasis

There are good chances that you will need any medicine considering your symptoms precipited by fatty and fast food. The symptoms most often subside in a few days. You may need antimotility drugs along with some antibiotics if they continue to persist. Contact your health care provider if you continue to have symptoms of tenesmus that are constant or come and go.

You would also need medical attention if you develop any of the following symptoms:
•     Abdominal pain
•     Blood in the stool
•     Chills
•     Fever
•     Nausea
•     Vomiting

In the mean time,
•     Worry less for symptoms as they appear to transient only
•     Avoid fatty and fast food for few days
•     If you are having constipation, simple measures such as increasing dietary fibre may help. Lactulose syrup can also reduce tenesmus.
•     Eat salad and XXXXXXX vegetables
•     Continue your healthy life style
•     Meditation, yoga and breathing exercises (helpful in cases of Irritable bowel syndrome)

I hope this information has been both informative and helpful for you. In case of any doubt, I will be available for follow ups.

Wish you good health.
Regards,

---