They are also changes we fight against, in my case is my body.
I am 22 and my metabolism is slowed down by a lot, most people would bang their heads against a wall and wait for obesity to kick in or blame it on doctors.
I will do the best I can to lose the extra pounds and maintain my weight after, even if that means eating less than others because my basal metabolical rate is smaller, working out more or not touching simple carbs.
Yeah that's also a big fight. I was just reading about that recently how Ryan Reynolds for example eats 6-8 times a day, very small portions to train his body to not store fat.. It's like re-programming the hard drive of one's own metabolism.
It's a fascinating subject actually. When your body needs food, some people treat it as a baby who is crying and you have to educate the baby step by step, don't feed him right away because it's not good for them, and little by little they get used to it.
Looking forward to read about your experience if you're writing about it. :)