Hi Sherra, great question!
I would recommend asking him some more questions and then introducing foods that will be easy for him to digest (for Vata), but without the pungent spices or hot sauces added (which will irritate Pitta). If he can avoid excess coffee, and alcohol, and drink only warm herbal teas and water, this will help. Soups, stews, all cooked veggies, stewed fruit in oatmeal, and soaking grains/legumes before cooking will be helpful for his body to digest and assimilate.
Some questions I would ask to get more information:
1) Does he have diarrhea every day, or only after certain foods? (frequency)
2) When did diarrhea start? (was there a trigger?_
3) What type of diarrhea is it? (Pitta’s will more likely be lighter brownish, may feel hot)
4) What are his Vata imbalances that are showing up?
Once you have these answers, it will be easier to recommend foods and practices for him. Sometimes, diarrhea can be a sign of excess damp and cold, like there’s no fire to digest at all so it moves quickly through the body. This is why asking what diarrhea looks like/feels like, and when it started, is helpful for food recommendations.
Let me know if you have more questions!
Warmth,
Riley