Your weight fluctuates. Its a function of your biology, your eating habits (diet), average level of effort throughout the day (work/gym/sports/free time). With no intentional effort directed toward weight gain/loss you will find your self at an equilibrium, or some unfortunate people find them selves never bottoming out and heading towards health issues getting too obese/frail. Maybe that is the case for everything in life. Our experiences geared us toward some level of prosperity/weight/love/enjoyment/pain. We can always attempt short burst of concentrated effort, like a diet, but it will do nothing in the long term, it needs to be a life style change to bring on any meaning full change in our equilibriums.