so you are what you eat.
No, you are not what you eat, you are what your unique body metabolism makes of what you eat. I know many who eat anything they want and do not gain any weight or fluctuate more than +- 5 pounds. They are not overweight; good genes like some of my family is what I would suspect.
I ate anything I wanted in mass quantities up into my 50s and never had a weight problem; I weighed a puny 145 lb at 6ft when I entered the Marines, 165 lb when I graduated from boot camp and throughout my military career never went above 185 as I aged. After some abdominal surgery, I developed a belly roll and put on an extra 10-15 pounds but the doctor says no problem and I’m in good shape.