Should junk food be banned from all schools & what exactly defines "Junk Food"?

Not all schools, just schools that actually need it. Some kids know better. They may have good examples at home while some don't. Obesity might also not be as rampant in their school district. My district is cautious and aware of it but we don't seem to have that problem if we compare class pictures to let's say.. From a district somewhere in Mississippi.

Junk foods are calorie dense but lack micronutrients. Tons of carbs and sugars which our metabolism processes right away just as fast as it stores whatever that is left over around your waist and thighs. Chips, soda, and candy. Things that when you look at, can't tell its caloric value by proportions. "Its just small bag of chips" omnomnomnom.  But it's not going to make you as full compared to let's say... An avocado.

The problem is not the food the problem is junior does no exercise has a note from home so he doesnt have to so he stuffs his fat face full of food all day looks at a computer screen and dies at age 30 because he refused to exercise and now is 450 lb

the schools in my area banned junk food long time ago. However. High school students are allowed to leave the school property during lunch without permission so they  just walk to the store and buy it.

(most high schools in my area are located across the street from a Dairy Queen or Mcdonalds, or some other type of restaurant lol and there is usually a convenience store within a block too.. fast food companies know that students can leave school at lunch so they build next to them)

my former high school is about a block away from a shopping plaza which also has pizza joints and asian restaurants. i would go there for lunch sometimes with my friends.

Yes for primary schools, but at college we can go off-site whenever we want and lots of people go into town for pizza etc. I think when kids are young the school has a duty to look after them more which includes giving them good food, but when they get older they will do what they want and there's nothing you can do to stop them. Besides, as teenagers, school should be about education because they should be able to look after themselves by then.

No

Banning almost anything doesn't help the issue , in this case , the parents have to assist youngsters and encourage exorcize,  Limit Internet

And gaming . Obesity wasn't so much a problem 25 years ago because kids had to go outside and actually make friends and play if they wanted to do something... Today it's different. One can entertain themselves for hours and never get out of bed.

So many schools have gone from actually making the food at site to having it "carted" in or out sourced.  Simple foods - cooked on site - and served by the actual cooks - would solve quite a few problems.

Junk food is food that is calorie-dense and nutrient poor. In recent decades, junk food, fast food and convenience food consumption in the United States have increased dramatically, with 25 percent of people now consuming predominantly junk food diets. Especially in teenagers. In my opinion, the Junk food must be banned from all schools. It is good for health.

I don't think that it's a good idea to ban junk food completely. When you're a kid you want to eat everything that isn't home-made. And if you forbid your kid to eat what it wants (at least from time to time), if you restrain him, it will all come back on a later stage. When he get to college or later on in life when he has the freedom to choose himself what to eat, he will go mostly for the junk food.

At least that's my opinion. 

And I speak from personal experience here. When I was 7 I moved to my grandparents (very strict people) for a couple of years. And then when I returned to my parents' house and I was able to do (and eat) whatever I wanted to, I totally lost control over what I eat. I ate two large packs of chips a day during one summer. Can you imagine?

So, you get my point, hopefully :D