You may be doing a similar exercise routine but if you measure the quantity of calories burned, and it is still 3000, then where do the extra calories come in for the fat deposition. Fat is a very calorie dense tissue. Perhaps you simply slowed your metabolism and didn’t burn the 3000 calories you thought you were burning. No question that different foodstuffs are metabolized by different pathways.
I exercise long and vigorously mostly because I enjoy it. I'm very consistent in that exercise. I know for certain sure that I will gain weight doing the exact same amount of exercise and eating very likely the SAME amount of calories per day if those calories come primarily from extended binges of junk food, as I have indulged out of laziness or weakness in the past, same exercise, and extra pounds on the scale to prove it.
When I switch to equally calorie-heavy things like cheese, carrot juice, sweet fruits, fatty meat like bacon and lamb (preferred over lean!!), heavily buttered veggies, mayo-heavy tuna salad, and egg-and-milk-based low-sugar fat-heavy treats like tapioca pudding, and put in the same amount of calorie-burn in exercise, the same exercise keeps my middle from getting pudgy.
No, it's not fewer calories -- just calories from different sources. What the books say and what the body does are two different things sometimes, and I trust what I experience more than what I read.