T Nation

Digestive Efficiency

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.

It’s possible, yes, that your body won’t absorb all those calories.

This probably really isn’t accurate, but it’s good enough for most purposes. Let’s say you technically ingest 2000 calories, but get 1800 calories worth of energy out of it. 90% efficiency. As long as you’re eating nutritionally similar foods that your body already is used to processing, you’ll probably get around 90% efficiency no matter how much you eat. So if you up that to 3000 calories, you’ll get 2700 calories of energy out of it.

Simplified into a rule of thumb, it really just becomes “eat more to gain” and “eat less to lose”.

It ultimately comes down to knowing your body. Some people can gain weight on a 2500 calories intake, some people lose weight on that same intake. In reality, this is probably because some people’s guts are more efficient than others – different flora, different intestinal lengths, better enzyme and acidity management, etc. And while all that stuff is interesting, it really doesn’t seem to matter THAT much. (Certainly at some point, it might be worthwhile to try and optimize it… but that’s something that can be held off until later.)

Probably the most reasonable way to deal with it is to try something, measure, and then adjust when you determine how your body reacts. If your body is heading in the right direction, keep doing what you’re doing. If it’s not, change.

I know that sounds overly simplified, but it works.

You do not absorb absolutely every calorie that you put in your mouth, though your GI tract is VERY VERY efficient at absorbing nutrients. So you get a whole lot of it.

In your example, if you were to suddenly increase your calories by a thousand a day, that’s 7000 a week. 1 pound=3500 calories, so does this mean you will gain exactly 2 pounds every single week? Not quite.

Not ALL of the calories will be absorbed (though the vast majority will), and your metabolism will increase a bit. So you aren’t going to get a full 2 pounds, but you will be pretty damn close.

In short, no, you don’t absorb absolutely every calorie you ingest. But it is pretty darn close. Close enough that you needn’t worry about it.