There are numerous types of potatoes. You know that they generally aren't low carb - but here are details about which are better than others.
To start with, 1/2 cup of potato has 14g of carbs in it. This is more than pretty much any other vegetable on the planet. While other veggies like tomatoes and zucchini are loaded with nutrients, the potato really has very little in comparison.
So why do people eat a ton of potatoes? First, they're cheap. You can grow a ton of potatoes very easily. Remember the Irish being forced to grow giant batches of potatoes? It's an easy-grow food. It grows underground, safe from deer, rabbits and such. Also, it is full of calories and carbs. While this may seem BAD to us in modern times, to hard working farmors and laborers, this was great. It gave you the energy to keep working.
Sweet Potatoes are, as you might guess, even worse for you. They are a high sugar version of the potato. They are a full 22g of carbs per half cup.
How about McDonalds French Fries? Be ready for this one - a large fries has 70g of carbs - and that's only 6oz of fries!! A medium order, at 4oz, is 47g. Never mind that they fry the potatoes in trans fatty acids. Talk about a double dose of bad.
I really recommend you wean yourself off potatoes - and find some of the other delicious veggies that are good for you!
Yam / Sweet Potato Information
Yams and sweet potatos are full of natural sugars, but they are also quite nutritious. In the grand scheme of things, they are quite better than many dessert style dishes you could feed yourselves :)
It's important to note that yams and sweet potatoes are not in the same botanical "family". Yams are part of the Dioscoreaceae family - found in the tropics. Sweet potatos are part of the Convolvulaceae family, related to morning glories! They are completely different types of vegetables. Neither are related at all to potatoes.
Sweet potatoes have:
28g per 1 baked sweet potato
27g per 1 boiled sweet potato (without peel)
59g per 1 cup mashed sweet potato
Yams have:
36g per 1 cup raw
If you're going for a candied yam dish or a sweet potato with brown sugar dish, realize that you are consuming a TON of sugar and should plan for a long walk afterwards :)
Tomato Nutrition Information and Types
Tomatos are a healthy staple of any diet, most definitely including low carb diets. Tomatos are full of great vitamins and are low in excess sugars.
A half cup of tomato only contains about 3.2g of carbs. Compare that with the 14g+ found in potatoes!! Plus you get way more nutrition out of your tomato.
What's fascinating is that only a short while ago, mankind thought that tomatos were poisonous! That's because the plant itself (the green part) is not healthy to ingest. However the bright red objects we eat are quite good for us.
What's even more fascinating is that a tomato is actually a fruit. It has all the botanical properties of a fruit. The only reason we call it a vegetable is because we tend to eat it as a food, rather than a snack. Interesting!
Some common types of tomato include:
Beefsteak - the large ones that are used, in slices, on burgers
Cherry - the teeny ones that are like marbles, used in salads
Roma - medium sized oblong ones, perfect for salsa and sauce
Some people try to figure out the carb differences between tomatoes. It's really very tiny, and since every single tomato is different than its brothers, it's best just to use the standard count as an average across all tomatoes you eat.