I would say its the consistency of weight training. When you weight train consistently you're building muscle and depending on your diet so your body can allocate the macronutrients (protein, carbs, and fats) accordingly. Either eating alot of calories high in protein, or restricting the calories should have a direct effect on body weight and composition over the long run. Over a span of 10 years gaining 10-20 solid lbs is more than reasonable.