· If you are eating within your caloric budget, you won’t gain weight

If the total number of calories you consume during the day (including your late night snack or meal) is equal to your energy needs, you won’t gain weight. After all, weight is determined by energy balance (and genetics). In general, if you eat fewer calories than you need, you will lose weight and if you eat more, you will gain.

· The nutritional content of food doesn’t change during the course of a day (or overnight!).

A certain food (i.e., an apple) will provide you the exact same quantity of energy (calories), vitamins and minerals whatever the time of the day you eat it. Eat it during the day- get 100 calories. Eat it at night- get the same 100 calories. **If you let food sit in your fridge for too long, it will contain less vitamins and maybe some extra stuff (bacteria and/or mold!) But this is another topic!

(tips for the girls and tips for the guys)

As a teenager, you have special diet requirements due to the sudden growth spurt and changes in your body. Now is the time to exchange the junk food for healthier alternatives. It’ll make you more attractive now and healthier later on.

Tips for the girls

Balance your energy levels. It's important to stay active when you hit your teens. Although your energy needs are high at this age due to all the changes in your body, adolescence can also be a time of weight gain if you’re not careful. Take part in sport and replenish your energy levels by eating moderate amounts of complex carbohydrates. These include starches rich in fiber, such as whole-wheat bread, fruit and vegetables.
Keep strong with calcium. Because of speedy muscular, skeletal, and hormonal development, your calcium needs have risen tremendously. Interestingly, 45% of your bone mass is added during your teens. So stock up on the milk, yogurt and cheese – but choose the low-fat or fat-free alternatives if you're concerned about your weight.
Bring on the fruit and veggies. Eating too little of nature’s own medicine can lead to cancer and other diseases later in life. At least five portions of fruits and vegetables are recommended per day.
Iron it up, baby. Due to the onset of your periods, a large amount of iron is lost every month. Iron deficiency can lead to anemia, which may impair your immune response and decrease your body’s resistance to infection. Anemia is also associated with a lack of energy and concentration ability – not a good thing if you want to keep up those good marks. Try to include iron-rich foods in your diet, such as liver, beans, potatoes, oats, raisins and dried peaches.
The skinny on fat If you're concerned about gaining weight, the answer is not to cut out all the fat in your diet. Some fats are actually good for you. Fish like tuna, sardines and salmon contain beneficial fats and should be consumed on a regular basis (at least twice a week). You should, however, try to cut back on pastries, baked products, junk food and sweets.
Start the day the right way. Stop that mid-morning doughnut craving dead in its tracks by eating breakfast – this way, you won’t gain those extra kilos. Plus, there’s no denying it: skipping breakfast has a definite effect on concentration and school performance levels. A generous helping of fruit, high-fiber cereal or oats, and milk or yoghurt will kick-start your day.
A to prevent acne. Vitamin A has been proven to be effective in the treatment of acne. It reduces the production of sebum – the white fatty substance found in the body’s pores. Find all the vitamin A you need in orange and red fruits and vegetables such as carrots, melons and tomatoes. Large amounts of vitamin A can, however, be toxic. So don’t overdo it.

Tips for guys
Cut the fast food. Your mom’s been telling you this for years. Fast foods tend to contain lower amounts of the right stuff: iron, calcium and vitamins A, B and C. These foods are usually sky-high in fats as well. If you eat out, try to settle for a healthier option such as pasta or a whole-wheat sandwich.
Hold back on the proteins. While protein is absolutely necessary for normal growth and development, you should be wary of overdoing it. Excessive intakes of protein can interfere with calcium metabolism, which can lead to osteoporosis later in life. Too much protein can also increase your fluid needs and this may put you at risk for dehydration while exercising.
Iron, man. Due to the build-up of muscle mass during your teens, the blood volume of your body expands. An increase in blood volume calls for an increase in dietary iron intake. It's possible to boost your diet with iron without including unnecessary amounts of protein. Try to include alternatives to meat such as potatoes, dried fruit, dark green vegetables and beans.
Zinc it up. This mineral is crucial to your body’s normal development, especially your sexual maturation. There is also some evidence that zinc can help in the prevention of acne. Work this mineral into your diet by eating moderate amounts of fish and shellfish on a weekly basis.
Fluid, fluid, fluid. It's very important to maintain a fluid balance at all times. If you're active, even more so. Exercise produces heat, and fluid is important for maintaining a body temperature that maximizes performance. A good sports drink contains all the right stuff to replace lost electrolytes. Drink at least a cup of fluid every 15-20 minutes during exercise and two cups afterwards.  

 Complete article at   http://bit.ly/JLQjBU  Additional information  http://bit.ly/1beWhRk

Best Teen Diets believes the best nutrients are found in lean meats, poultry, fish, beans, eggs and nuts; fruits and vegetables; whole grains; and low-fat or fat-free dairy products.  Crafting a diet that addresses your individualized nutritional needs will establish the foundation for a lifetime of healthy eating habits.