How do they do it?
My brother lost a lot of weight a couple years ago, and is trying to maintain it, while also working on toning and strengthening. As such, he eats only low calorie foods. When he needs to get more calories in him to support his excercise routine, he will cram more low-calorie food down his throat, or else just skip it, rather than eat something a little richer. My opinion of what is healthy differs from his. I believe that the closer you can get to natural, the better it is for you, even if it does have more calories. Just because someone figured out how to remove all the fat and most of the calories from something, doesn't mean it's good for the body.
So, the other day, I was trying to explain to him what I've learned about long fermented bread having much better nutritional value than the commercially produced bread he buys. I told him it would be healthier, and offered to bake a sourdough loaf for him. He pointed to the calorie content label on his bread bag, and it claims to have 80 calories per two slices of bread! He said if I could make bread with that many calories or less, he'd try it. The bread he buys is whole grain, and claims to have 20% more fiber or something like that.
I told him I thought I could do it, but now that I've been doing the math, it seems impossible. The Whole White Wheat flour I bought has 100 calories per 30g of flour, and it doesn't claim to be bread flour. If I make a pan loaf, in a 8.5 x 4.5 pan, and get 16 slices out of it, I would need the loaf to total 640 calories. If I made a simple lean dough, and the flour was the only thing that contributed any calories, I could use 192g of flour. That is just over 40% of the amount of flour I normally use for that size pan. And I'm used to baking with white bread flour, so it's gonna be a real challenge to get anywhere near what he's asking for. So, what can I do? Is there a way to fill out the volume of the loaf without adding a significant amount of calories? I'm trying to do this with ingredients that come from the earth, not a laboratory. That may be the part that makes it impossible.