这里是一个类似老方的观点的健康Q&A
http://askkaren.custhelp.com/app/answers/detail/a_id/5848/~/is-corn-a-grain-or-a-vegetable%3F-------------------------------------
Corn can be considered either a grain or a vegetable, based on when it is harvested. The maturity level of corn at harvest affects both its use at meals and its nutritional value. Corn that is harvested when fully mature and dry is considered a grain. It can be milled into cornmeal and used in such foods as corn tortillas and cornbread. Popcorn is also harvested when mature, and is considered to be a whole grain.
On the other hand, fresh corn (e.g., corn on the cob, frozen corn kernels) is harvested when it is soft and has kernels full of liquid. Fresh corn is considered a starchy vegetable. Its nutrient content differs from dry corn, and it is eaten in different ways -- often on the cob, as a side dish, or mixed with other vegetables.
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简单地说,这个决定于在玉米的哪个成长时期收割玉米。
当玉米完全成熟的时候,米粒会变硬,这就是老玉米,一般都是磨碎了作为粮食。爆米花的玉米就是老玉米,烤玉米应该也是老玉米。
当玉米新鲜时候,米粒充满液体,是又软又甜的,这时候就是当淀粉类蔬菜 (starchy vegetable)和水果来吃。通常这种吃法是有玉米棒子一块上桌的,比如肯德基的玉米棒,或者混合其他的蔬菜一起吃。