My father is diabetic and usually complaints of indigestion and loose motion .what could be the possible reasons and immediate treatment?

Lots of possibilitie: Those symptoms are nonspecific and can be due to many possibilities, some of which are diabetes related, some not. If he is taking metformin to treat diabetes, a common side effect is diarrhea and stomach upset.

Paleo diet: The easiest way to improve digestion, diabetes, reduce weight, cholesterol, is by completely stopping grains, lentils, potatoes based items. Also avoid milk protein (milk, yogurt, cheese) since it causes indigestion. Healthy food items such as eggs, fish, chicken, meats, vegetables, some saturated fat (butter, ghee, coconut oil), olive oil are very effective. Take a probiotic (Megafood) daily.