Apparently, lesbians tend to be overweight, and gay men tend to be in great shape. Statistically. So says science! Federally funded science, now that you mention it:
"By now, you’re probably wondering why the government is funding a study that, so far, has largely reinforced stereotypes of gays and lesbians."
I wasn't completely up to date on the stereotypes, myself, so I wasn't actually wondering that.
Anyway, they don't seem to have a very good reason for either of these countervailing tendencies. But, to me, it looks like you could explain a lot by a different old stereotype - namely that men tend to be more attracted by visual features. This might result in those who are trying to attract men - namely straight women and gay men - working harder to achieve slenderness.
Of course, stereotypes abound,
and I'm not sure which ones are sound.