All these things tie in together. Every system in your body is connected, thus, any change made to any part of you body will effect all others. The evidence of change might be so small that you don't even notice them, but you need to remember that everything you do to your body causes for some sort of a chain reaction. We can and should use this to our advantage by doing things that are good for our bodies, resulting in us feel better.
Studies have been done proving that people who engaged in exercise, reported improved mental health.
When I have a lot of "steam" built up that is just making me unhappy and stressed, I go right outside, grab the ax and split some wood. That kind of exertion of power- fast and intense- (like weight training) can really help you get out what has been building up inside. For some people, a long run, outside on back roads, surrounded by nature, is a great way to relieve stress and calm the nerves. It is often nice to step out of the world for an hour and just go explore, alone. It leaves you with your thoughts, the wilderness, and without society. Even going to the gym, sticking in your headphones and running on the treadmill, or jump-roping, of lifting, can helping get out of the "rush, rush, rush" and worry, and just be there in your body. Some people stress about their weight and constantly worry about what they are eating, and then feel guilty after eating a big meal. That stress can also be eliminated by exercising. If you can tell yourself that you just ran for 20mins and burned 500 calories, maybe you won't worry so much about the calories you take in afterward.
There are so many reasons why you should exercise, and the ones that I just mentioned are just a few of the emotional perks of physical activity. Now, we need to remember that not only exercise will change how you feel. You need to keep a healthy, balanced, diet and make sure you don't skip any of those essential proteins, fibers, vitamins, fats...etc. Deficiency of any of these crucial part of your daily nourishment can result in low energy and energy, irritability, trouble focusing, and in the long run: breakdown of lean muscle. "You are what you eat." often helps me remember not to treat my body as a trash can and to only eat the things I know my body needs, and to stay away from fast food and foods with a low nutritional value.
~Iolani