I have dabbled in weight training for over nine years, but only recently have figured out that if I want results I need a program. I have started stronglifts 5x5 and have been reading up. The question I have is about diet. A lot of articles talk about how to gain weight you simply need a caloric surplus and to lose weight, a deficit. If you feel you're a hardgainer, you probably aren't eating as much as you think, etc. These articles often cite physics, etc.
To put it bluntly, my question is about poop. Does your digestive system necessarily take in all the calories you eat? Does the percentage of calories that your body digests vary based on how many calories you consume/what kind of calories you consume? If I add 1000 calories to my diet, isn't it possible that I will just poop more or my poop will be more calorie rich. Conversely, if I cut calories, might my body work to increase my digestive efficiency?
For the record, I 215 pound at 5'10." There's a fair amount of fat so I'm not really trying to gain weight. I'd like to try to get my lifts up while maintaining this weight and then see what I look like with more muscle. So far, my diet strategy has been to increase protein and cut out processed sugars.