Hi Pauline,
Answer to your question is yes, provided they are not tinned prunes in syrup. I pulled this off a healthfoods website for you:
"Prunes' soluble fiber helps normalize blood sugar levels by slowing the rate at which food leaves the stomach and by delaying the absorption of glucose (the form in which sugar is transported in the blood) following a meal. Soluble fiber also increases insulin sensitivity and can therefore play a helpful role in the prevention and treatment of type 2 diabetes. And, prunes' soluble fiber promotes a sense of satisfied fullness after a meal by slowing the rate at which food leaves the stomach, so prunes can also help prevent overeating and weight gain."