Interestingly, in most parts of the world there are fewer boys being born. In Canada, which is every bit as fat a nation as the USA, there is a highly inordinate amount of boys being born.

Check this wikifile out:

Son Preference and Sex Ratios

For some reason Canada appears with countries like India and China where female infanticide has been (and is) rampant.

Ireland and Portugal appear to be in the same boat, for whatever reason. It does suggest that obesity and infertility may not be linked to more girls.

In the largest populations in the world (China, India) there have even been long-term predictions that a sort of polyandrous (multiple male spouses) may be the only solution for young men to marry at all (that or immigrate somewhere with a better ration of females to males).

Just my 3 cents