It really doesn't. Low carb. If it's bread or contains sugar, it's not low carb. That's pretty simple.
The body doesn't prefer one or the other. One could argue the opposite; before agriculture, humans ate primarily animals. Meals were few and far in between. Google the Warrior Diet. People throughout history utilized keto with intermittent fasting.
(for the lazies:
https://en.wikipedia.org/wiki/Warrior_diet)
You can gain mass on a ketogenic diet. Lean gains, look it up. Cutting is a caloric deficit. Adding mass is a caloric surplus. Again, simple. It's just easier for most to cut on a ketogenic diet because fat is one of the most satiable substances you can consume, and protein protects you from muscle loss. Your blood sugar and insulin levels stay relatively the same throughout the day, so you stay fuller, longer.
There's no basis for fact, whatsoever, in that statement.
The research is out there. You can choose to expand your knowledge or deny what evidence has been brought forth. I find it all very, very interesting, and not one method or set of groceries fits all. I like experimenting, and after being vegitarian/eating only fish/keto/zero carb, zero carb is my favorite so far; I choose steak over quinoa. :rolllaugh: