The less packaged food you eat, the easier it is to avoid sodium. When I eat only whole, fresh foods, I have a nice, low sodium intake. Add just a couple of packaged items in a full day, and it goes up pretty quickly. Avoiding table salt is also very helpful; you can use other flavoring agents during cooking to get more flavor.
I was unfamiliar with the terms "fast" and "slow" carbs but I've heard similar terminology many times and I assume it's related to glycemic index and/or glycemic load, so you can probably find the answer to your question if you google that. Or use one of my favorite nutrition sites, which gives a TON of information for a TON of different foods, including glycemic load: http://nutritiondata.self.com/
According to that, raw pumpkin has a glycemic load of 3, which I believe would make it "slower" than raw sweet potato which has a glycemic load of 11. Cooking or canning would likely change that a bit, but the site has values for those, too.