It's not that authentic, but switching out spaghetti for soba noodles is an easy way of lessening the carbohydrate and calorie load you'd usually get with a simple bolognese dish.
If you don't mind the different texture and flavour, the average cup of soba noodles contain 113 calories and 24g a carbs, compared to the 221 calories and 43g of spaghetti, as noted by Live Strong. At home, we've been using udon as well, which isn't as healthy but still a good alternative.
Considering a lot of flavour will come from the sauce and protein you use, you'll be surprised at how small the effect is on the overall taste. Obviously, purists won't be satisfied, but for everyone else, I urge you to give it a try!
Japanese Noodles & Weight Loss [Live Strong]