If my understanding is correct, net carbs is total carb grams minus fiber grams and since it takes your stomach more time and effort to process the fiber the carbs don't enter your blood stream all at once and therefore don't produce the spikes in blood sugar levels. Fast processing or slow processing, the carbs must still be processed so I look at total carbs only. Take this with a grain of salt since it's just my musings and has no basis in science.