Why is popcorn not the same classification as corn?

The USDA in the dietary guidelines for Americans defines popcorn as a whole grain and corn as a starchy vegetable. I'm confused on why there is a difference, are they not the same part of the same plant, just with different water content? What makes them different?

Answer

On top of everything listed here, popcorn is often cooked in heaps of oil and butter too !

And a serving of popcorn, because of the air content, is much less nutritionally dense than normal corn

A normal serving of corn is approximately 73g or 1/2 cup. A single serving bag of popcorn is 13g or 1/10 of a cup.

So something that provides little calories, carbs, protein, fats and sodium in a serving is not seen as equivalently healthy because food is healthy when it’s nutritious. If we ate 5 single serve bags of popcorn in a sitting and that was a serving size, it might be seen by the authority as quite nutritious.

BY SERVING SIZECobs Natural Sea Salt Popcorn

64kcal
1.5g fibre
6.7g carbs (<1g sugars)
3.2g fat (<1g saturated)
47mg sodium
1.4g protein

USDA Corn Nutrients 1/2 cup

62kcal
2g fibre
14g carbs (2.4g sugars)
0.9g fat (0.1g saturated)
11mg sodium
2.4g protein

PER 100gPopcorn

495kcal
11.5g fibre
51.6g carbs (>1g sugar)
24.6g fat (2.2g saturated)
360mg of sodium
10.9g protein

Corn

65kcal
2.8g of fibre
7.7g of carbs (3.6g sugar)
2.1g of fat (0.5g saturated)
241mg of sodium
2.6g of protein.

So popcorn is much more nutritious per 100g, but per serving size, it’s less nutritious than corn kernels