A bunch of my running friends (who are rather speedy) are all pretty lean. But yet, I eat a lot better than they do and I dare so I focus on strengthening my core more than they do.
Could this be because of genetics? My dad's side of the family (and all the men in my family, really) aren't necessarily skinny or fat, but do have a bit of extra body fat.
Seeing as how lower percents are better and I'm at around 10-12%, how could I become leaner?