It's very true that the more we sink into a depression or lethargy, the harder it is to climb out of it. Many people who are out of work fall into this trap. Your brain gets used to the lethargy and begins to think that it's just not possible to do anything else.
That's why little steps are so key. The little steps help show your brain that progress can be made. It builds up the confidence and energy levels to try for that next step.
Eating well is definitely a base key. If your brain doesn't have nutrition, it can't function well. It becomes sluggy. It's hard to do things when your mind is in a fog. I definitely find in my own life that I can have a day full of energy - or a day where I can barely get off the couch - based on the food I eat. There are some foods that just sap my will to live.
For calcium, I eat Tums orange chewables. To me those are tasty.