1 cup of brown rice is 216 calories, with 45g of carbs and 3.5g of fiber. (fiber/carbs = .077)
1 cup of cooked spaghetti pasta is 220 calories, with 43g of carbs and 3g of fiber. (fiber/carbs = .069)
1 slice of white bread is 120 calories, with 23g of carbs and 1g of fiber. (fiber/carbs = .043)

Then there are glycemic index and glycemic load: 50 and 21 (respectively) for the brown rice, 82 and 21 for the potato, and 46 and 22 for the pasta. In comparison, white bread has a glycemic index of 71 and a glycemic load of 10!

So I know that white bread is "bad carbs" and that brown rice and potatoes are "good carbs" (I'm not sure about pasta!). But WHY? The glycemic index and glycemic load of white bread are lower than a potato...

I am not trying to go "low carb", I just want to understand why "good carbs" are good and "bad carbs" are bad... there has to be something more to it than their "processed-ness", some scientifically-measurable reason why potatoes actually better than white bread... right?

And where does pasta fit into all of this, is it a good carb or a bad carb, and why?

Generally good carbs= complex carbs, bad carbs= simple carbs. Hope this article helps
http://www.fitday.com/fitness-articl...ohydrates.html

Thank you!

But from what I can understand from the article, the carbs in all of the items I listed are starches (and therefore complex carbs), not sugars (simple carbs). So if a potato and white bread both have their carbs as starch, why is the potato better?

(...and where does pasta fit into all of this? Even regular non-whole-grain pasta, which I gave the numbers for above, seems to be about equal to brown rice, even though it is made with refined flour just like the white bread...)

There are a number of sources to support whichever claim you want to believe. This is a big problem. People pick a side and then gather data to support their belief. You can do much better than that. I've trusted the low carb movement before eventhoigh deep down inside I knew there were huge gaps in the logic. In the end I decided to let my body do the thinking instead. I give it what it asks for and then pay close attention to how it reacts - more energy? Less energy? Satiation? Etc. and I have come to a really nice gentle implementation of carbs and sugars in my diet. Enough to fuel me but not enough to make me feel lethargic.
There is no good or bad, right or wrong. Finding balance is what's most important. Food is food and some food makes me you feel better and other food makes you feel icky. Go with "better" and keep the icky stuff to a minimum.

The problem with white bread is that it is refined grains. Refined grains have had nutrients removed from them during the refining process. Nowadays white bread has some nutrients added back (this is called enrichment), but it isn't all of them. Whole grains have more nutrients.

Refined grains turn to sugar faster than whole grains. Whole grains will turn to sugar also, but more slowly. So for many people whole grains are less likely to spike the blood sugar (there are some people who get spikes with whole grains though). Food that has fiber in it usually turns to sugar more slowly than foods with less fiber.

My guess, at least with how my body works, is that bad carbs (i.e. processed) tend to hit my blood fast, spike my insulin and prime my body for fat gain from any food I subsequently eat, specifically food high in fat.

Good carbs (i.e. unprocessed) hit my blood more slowly, leading to less of an insulin response and subsequently less fat gain from any food I then eat.

So, in simple terms:

I would get fat eating chocolate chip ice cream (bad carbs) and lots of cheese.

I would not get fat eating dates, dried figs, Turkish apricots (good carbs) and lots of cheese.

Note: under both scenarios, I would not necessarily lose weight. To lose weight I would need to cut calories. But fat gain is different to muscle gain which is different to fat loss and muscle loss. Weight loss is not binary. We need to operate in two dimensions: fat and muscle.