actually this makes sense

Having a hearty appetite, eating potassium-rich foods including bananas, and not skipping breakfast all seemed to raise the odds of having a boy.

The British research is billed as the first in humans to show a link between a woman's diet and whether she has a boy or girl.
...
Dr. Michael Lu, an associate professor of obstetrics, gynecology and public health at the University of California at Los Angeles, said the results "are certainly plausible from an evolutionary biology perspective."

In lean times, more females would be born; in good times, the sex ratio would be more nearly equal. Since males can fertilize more than one female, fewer males are strictly 'necessary', and indeed they might be a drain until resources are more plentiful.