Humans are creatures of habit and it's very easy to remain in a state of perpetual complacency. As life goes on, we reach points that feel comfortable, so we stay there instead of venturing outside of our comfy boxes and into something with a greater span.
The definition for complacency is this:
Complacency seduces us with quiet pleasure but has great potential to harm us. When we get stuck in life, and there is no change happening, we have no other option but to regress or go backwards. There is no such thing as being in a spot of maintenance when it comes to your life, you are either progressing or regressing, there's no in between.
Muscles grow when there is resistance placed upon them, if there is no resistance placed upon them, over time, not only do they not grow, they become weak. Again I say, there is no such thing as maintenance. People have become complacent with their diets, and they want change, but are not willing to get out of a place of complacency. They (the proverbial "they") would rather talk about changing than actually change, because change means getting uncomfortable for a little while. Here is some helpful advice, change in anything is uncomfortable. If you refuse to accept that, you will have to live with the long term pain that comes from living an unlived life over the short term pain of being uncomfortable in a new situation.
A sign of true health is being able to adapt to any situation. Your body has to adapt to change, or else it will die, and though change doesn't always feel great, I'm 99.9% sure you're not going to die. If you die, I apologize, but that means your body wasn't able to adjust accordingly and you're better off this way. Survival of the fittest. I'm kidding of course.
Joking aside, this concept applies to virtually everything in life. Change isn't a big, bad, scary monster, it's there to help you progress and to get out of a place that is keeping you from achieving your goals. For example, when it comes to your eating, try cutting out sugar for a week and see what changes occur in your body. Because the side effects from consuming sugar are the same as consuming drugs, when you halt consumption your body is going to fight back by going through a with drawl. Any addict knows the hell that's associated from with drawl, but the outcome after you have pushed through the pain is worth every minute. Change what is working against you, and keep what is working for you. I will leave you with one last quote from the band Trooper:
"If you don't like what you got, why don't you change it. If your world is all screwed up rearrange it"