Hi @celia16, when I was a child I had chronic diarrhea and I was on a strict diet - dry toast or saltines with jelly, pretzels, applesauce, bananas, no milk. Coke and gingerale were okay; also apple juice, but nothing else. Tea and sugar, no milk. Once I went to a friend's house, had peanut butter, and an instant reaction!
This was in the 50s. Things might have changed.

Maybe your dad should be checked for an infection. Have you spoken to your dad's doctor?

I did a search on Perplexity.ai:

To prevent diarrhea, it's best to follow a balanced diet that includes foods that are easy on the digestive system and help firm up stools. Here are some key dietary recommendations:

Foods to Include
Soluble fiber: Consume foods high in soluble fiber, which absorbs fluid and can help lessen diarrhea. Good options include:

Ripe bananas

Applesauce

Cooked potatoes (without skin)

White rice

Oatmeal

Binding foods: These help firm up stools and include:

Toast made from white bread

Plain white rice

Unseasoned crackers

Lean proteins: Opt for:

Chicken (steamed, baked, or grilled)

Fish

Lean ground beef

Eggs (scrambled)

Probiotic-rich foods: These can help maintain a healthy gut flora:

Yogurt (if not lactose intolerant)

Hydration
Stay well-hydrated by consuming:

Water

Clear broths

Oral rehydration solutions

Herbal teas

Eating Habits
Eat smaller, more frequent meals throughout the day

Consume foods at room temperature, as they may be better tolerated than hot or cold foods

Foods to Avoid
High-fiber foods: Limit intake of:

Whole grains

Raw vegetables

Nuts and seeds

Fatty and spicy foods: Avoid:

Fried foods

Sauces and gravies

Highly spiced dishes

Gas-producing foods: Steer clear of:

Carbonated drinks

Beans

Cabbage, broccoli, and cauliflower

Foods with laxative effects: Avoid prunes and prune juice

By following these dietary guidelines and maintaining good hygiene practices, you can help prevent diarrhea and promote digestive health.