There are lots of different goals and definitions for "fit", "healthy" etc.
I don't gain weight easily naturally. All my life I focused on putting on muscle mass and getting stronger. Decades later after understanding my body, I can do that well and my body has adapted to a degree.
My most helpful pursuits were studying old time circus strongmen. They were farmers who became wrestlers and entertainers. They created the equipment and many methods that joe weider later adopted for bodybuilding to become modern practice.
I found these old time strongmen still were stronger pound for pound and set records nobody today has yet beat. How did they do that without money, 'roids, and complicated equipment?
1. Typically, if food came in a package they didn't eat it. In other words, if it isn't right off the farm, forget it.
2. They trained with methods not used today- they used bodyweight routines that made use of isometric exercises, H.I.T training, and powerlifting techniques all in one. This actually forced natural hgh production in the body.
Later they developed this same method using dead weight like iron, sand, water, etc.
3. They knew how to relax.
So I have found in order to do that today, this is what I do:
1. Convict conditioning is a book that shows the same things the muscle beach guys used to do which the strongmen did. All body weight. No real equipment needed.
2. Isometric routines are illustrated in another book by the same author and they are not "therepudic" routines you get from a doctor. These are used in the Olympics. Again, no equipment needed although half the book is a sales pitch for their equipment they created.
3. I don't eat anything impure if at all possible. I know we can't control food manufacturing and on the road sometimes you just gotta get a burger. Otherwise, my simple meal plan might look like- eggs and raw fruit for breakfast, celery and peanut butter with some fruit for lunch, and burger patties for dinner with fruit on the side.
No preservatives, real food.
I also spend what I would have spent on bread or other foods I shouldn't eat on a subscription to a martial arts class. I already have training materials but I can get real instruction with a class. This improves my cardio, strength, and relaxation too.
So my costs for food are less than most, I have a muscle building routine that is completely legendary for the price of 2 books, and my martial arts training is so small in price you could add it to the food and I'm still paying less than most for my food.
So that's how I do it.
And I have strength equipment I have used for decades that I realize I don't even need now like custom made strongman dumbbell bars etc. But I have found my results from the above are superior.