This blog post was pointed out to me as challenging on the "2 seconds per mile per pound" theory that Runners World had put forward many moons ago.
As a man of science, I buy most of it, and I'm a bit irked that Runners World presented so much as fact based on what was really one study. Lots of extrapolation and overreaching from scant evidence.
What I do take issue with is this statement:
That adaptation might involve weight loss, it might not. Either way, you’ll run faster because you trained to run faster.
That's a bold conclusion, and supported by as little evidence as Runners World. Further, it doesn't speak to whether you will run to your potential, which is really what people want to know.
If I do the same training and also drop 10 pounds, would I be even faster?
I'm very convinced that for myself the answer is "yes". I have results from many different weights, and it is the single biggest factor in how I perform.
It stands to reason that more weight takes more energy to lug around. Obviously you can take that to extremes and hurt performance - lose the muscles you need to move yourself around, and that's not good either... so there's a point where it becomes counter-productive. At my weight and BMI, I'm nowhere near that point, so healthy weight loss here I come.