What specific foods should you limit or avoid?

1. Fats

Fast food contains extremely saturated fats. Eating an excessive amount food containing saturated fats can cause many cardio vascular problems,and long term effects such as diabetes, high cholesterol, etc. Some examples of saturated fats are animal fats, processed foods, cheese, cocout oil, chocolate, etc.

2. High in sodium
Too much salt in a diet can lead to muscle cramps, dizziness or electrolyte disturbance, which can cause neurological problems, or even death. Too much sodium in a diet can lead to strokes or other cardio vascular diseases.It's good to avoid foods such as processed cheeses and meats, certain canned meats like spam, salted snack foods such as pretzels and popcorn, etc
3. High in sugar
Some effects of high levels of sugar in a diet are:
- obesity
• diabetes
• heart disease
• an overgrowth of pathogenic intestinal flora
• gout
• panic attacks
• hyperactivity, and
• depression.

Many foods today are high in sugar. Many foods you might not even know are high in sugar. For example, ketchup is made up of 1/3 sugar. Also, some health foods are full of sugar for example, the average granola bar is packed with sugar. Avoid foods such as donuts, chocolate bars, candy, cereals that are high in sugar, fruit juices that contain lots of sugar, etc.

It's particularly important as a teen to eat healthy. Learning how to eat healthy as a teen will carry throughout your whole life. If you learn as a teen then it will create good eating habits for the rest of your life. Also, during teenage years is when the body grows the most and if teens aren't eating healthy it can stunt the growth and cause long-term problems.

http://www.monumentalmassage.com/articles/foods_to_avoid.html
http://www.copperwiki.org/index.php?title=Saturated_fat