Small amounts of coconut flesh are generally safe; oils and large volumes can cause digestive upset.
Coconut is not classically toxic, but the medium-chain triglycerides in coconut flesh, milk and oil can cause loose stools, diarrhea and stomach upset in larger amounts.
Coconut contains medium-chain triglycerides that dogs digest differently than long-chain fats. Coconut water is high in potassium, which in large amounts can disturb electrolyte balance — particularly relevant for dogs with kidney disease.
Surse
Occasional small bites of unsweetened coconut flesh are fine for most dogs. Avoid sweetened coconut and very large servings of coconut oil.