I'm 5'11" and 135lbs. I have a slender frame (wrist barely 6 inches). I work out regularly, but having a runner build [with hint of swimmer build

] I will never get big muscles. They are defined, though. Although my body fat is low enough for a distict 6-pack abs, and for my pec muscles to show the ripple when I flex them, I am certainly not ripped to bodybuilder standards - when I pull on a pair of underpants with firmly gripping elastic in the waistband, there is a definite (albeit small) ridge of fat around the waist.
Two years ago I weighed 145lbs. I lost 10lbs over a year when I stopped my previous practice of alternating 2 weeks heavy eating (weight training) with two weeks light eating (cardio). I've been idly curious this year as to why my weight levelled out a year after the change. Over the last couple of months I deliberately restricted my calorie intake by about 1500 calories a week and dropped to 132-3 lbs but my body rebelled - extreme tiredness after midday meal, carb cravings before bedtime, so I abandoned that experiment. Basically then, my weight is self-regulating around 135lbs - if it rises a few pounds I feel less hungry at breakfast, and I've seen what happens if it starts dropping too low!
Motivation for weight control? I read years ago that men who are no heavier than they were in their late teens have only one-seventh the incidence of heart disease than men who are heavier. I can't remember where I read it, have never seen it since, and frankly I doubt whether it's true. But anyway, I feel no inclination to aspire to be any heavier than my body self-regulates to on a diet (which I'm happy with) of rather bland, plain, mainly unrefined food.