There is no evidence to suggest any foods have net calories (except perhaps straight water), but most people consume salads with meat, simply for palatability and satiety. It's just a given I think that people consume spinach, brocolli on a cutting diet - otherwise u'd be very hungry in the evening and furthermore, you'd be relying too heavily on supplements for nutrition and fibre.
Many vegetables have a very small amount of net carbs (e.g., spinach, brocolli, mushrooms, tomatoes) and most are very nutritious.
The liquid taste of fish oil isn't too bad, and if you don't like it, just drink water afterwards. For me the taste then dissipates.