" With each little bit of exercise I did, each time I chose to move a little more, everything became easier. My brain was juicing up on all those good neurochemicals—all that serotonin, dopamine, and norepinephrine began making things happen. The BDNF was silently working away. As a result, not only did I have a bigger appetite, but food tasted better, and I wanted to eat healthier foods. I didn’t worry about things as much, and my sleep improved. I felt like I had more free time and even felt younger. Then exercise became more appealing, and slowly I became intrigued by the thought of a marathon. "

― Alex Korb , The Upward Spiral: Using Neuroscience to Reverse the Course of Depression, One Small Change at a Time