SELECT user_follows_diet.diet_id, AVG(user_rates_restaurant.rating_grade) AS 'Average rating' FROM flavours_without_borders.user_rates_restaurant JOIN flavours_without_borders.user_follows_diet ON user_rates_restaurant.diet_id = user_follows_diet.diet_id WHERE user_follows_diet.user_id = 1566 AND restaurant_id = 4330 GROUP BY user_follows_diet.diet_id