you need to burn more calories then you take in.
lowering your calorie intake will help. beings they are suggesting such a low calorie intake, i'm guessing you are not very active, so you need to exercise.
Since you are 17, 5'7 and 145lbs. so you really don't need to lose weight but can safely loose some. CC's calculators only work for those aged 21 and over. You are also very active (runner) so by my calculations using the calculator in 1b you burn 2800 with 1 hour intense exercise, eight hours sleep, and the rest of the day on your rump. So 1800-2000 should be your minimum intake. You may find that increasing your intake will help you lose because your body is more likely to release its reserves when it is given adequate fuel. Also when you are already at a healthy weight it is harder to loose with a larger deficit. Teenagers need more calories than adults as their bodies are growing. Even if you don't grow taller your organs, brain, bones, muscles etc are still going through vital growth and will continue to do so until at least age 21.
1. a. and b. BMR versus daily burn (because people always mix that up).
1a. BMR is your basal metabolic rate or what your body needs to maintain your basic life sustaining functions (i.e. breathing, heart beat etc.) if you are bedridden/in a coma. I think we can safely assume you are not bedridden or in a coma. You never eat below your BMR because that is the bare bones minimum to keep you ALIVE.
1b. Daily Burn is how many calories you burn a day with all your activities factored in. You can calculate this without your exercise and then add it in when you decide to do exercise or if you exercise regularly you can factor it in from the get go. A good calculator to get a good idea of your daily burn/calorie needs is this one http://www.health-calc.com/diet/energy-expend iture-advanced. This one is ok for teenagers to use because it calculates based on all your info age, gender, weight, height and activities.
2a. 1500 (girls)/1800(boys) calories is the bare minimum for short (less than 5') sedentary teenagers to lose weight.
2b. 1200 is the bare minimum for short (less than 5’) sedentary, older women to lose weight. (1500 for men).
2c. CC's calculators are for 21 and over. Teenagers have very different needs because their bodies go through vital growth up until at least age 21. They might not get taller but the brain and other organs, bones, and muscles all have a lot to go through. Because of that and the fact that they are young with higher metabolisms they need more calories.
6. Under eating will slow/damage your metabolism etc. When there is a drought you limit your water use to keep the reserves full so that you can last through the drought. Your body does the same thing so instead of releasing reserves it holds on to everything it has. Under eating/malnourishment forces it to draw nutrients/fuel from bones and muscle resulting in high risk of osteoporosis and other worse damages to your body. Even if you are eating foods with a lot of nutrients your body can't use those nutrients effectively without enough fuel.
7. Carbohydrates, Protein, and Fat are all vital nutrients for your body.
Carbs:Your brain does not burn protein or fat in burns glycogen ie sugar ie carbs. If you aren't feeding your body carbs it has to take them from your glycogen stores and those are located in your muscles. This is a good time to note your heart is a muscle. Complex carbs are also important because you need to pair them with protein to get a complete protein. Brown rice, whole grains.
Protein: Feeds muscles, helps you feel satisfied/full, gives energy. Lean meats, lentils, beans.
Fats: Fats don't make you fat. Fats are essential for healthy hair, skin, nails, digestion (lubes up the works), and for menses if you are a girl. In other words if you want to maybe be a mom someday you need to take care of yourself now. Fat also keeps your organs insulated so they stay warm and safe from damage. Fat gives you energy and helps you feel satisfied/full. Healthy fats include avocados, olive oil, nuts, nut butters and so many more.
8. Myth: Eating after a certain time will cause weight gain: This is not true eating after a certain time WILL NOT cause weight gain. Actually some people find a night snack, like an apple and some milk, helps them sleep through the night better and not wake up hungry because it stabilizes blood sugar overnight. I'm not saying you have to eat it right before bed or anything but if you wanted a little something in the evening after dinner that is ok.
9. Healthy weight: The goal should never be to lose as much as possible, as fast as possible by eating as little as possible. It is not sustainable and you will yo yo back to where you started and it is in no way the healthy way to go.
There is no good reason that anyone needs to be at the very bottom of the healthy weight range unless it is just where they naturally are. By naturally I mean eating maintenance calories or more w/o excessive exercise and not gaining or losing, basically the set point for your body. Not very many people fall into that category. In fact many people can be the same age and height but be two different body types so that one end of the scale is healthy for one but not the other. Everyone is unique. The best thing you can do is get your doctors opinion in this matter. Plus it never hurts to get your health checked.
The aim should be to have a healthy strong body that will carry you for a lifetime.
I know I practically wrote a book but I hope you find some piece of it helpful. Good luck and please be healthy and nourish your body because you deserve to be nourished and loved in all ways. All the best.
Thank you, that has helped me understand a lot more about how many calories I am meant to be eating.
I'm glad it helped. Good luck and good health!