Help me understand calories

[Yobz]

People say that 1000 calories from junk food is different than 1000 calories from fruits/veggies. I want to make sure I understand why.

The differences I see are this:
- Sugar-based junk food will give you an insulin spike and make you hungry again soon
- Fruits/veggies have more vitamins/minerals/etc

I don't see the difference between pretzels, for example, and fruit. Besides the vitamins/minerals, they are both carb-heavy. I guess the biggest difference is that pretzels are so dense, so it is easier to eat a lot of them as opposed to fruit which have lots of water and eating 1000 calories of apples is difficult. You'll get full or sick of eating before you make it through the meal.

Any help?
Thanks