A quick question (and an easy one to answer, I think.)
When I publish my page some-but not all-of my line breaks disappear.
I've done some investigating at the wordpress.org forum and read that it was a css issue. Seems if it were though that all the line breaks would go away, not just some. What I'm calling line breaks are like

this.
Thanks

I need to see an URL with the error

Sorry Flynn,
It's here

If you mean the lower part starting with "If you now eat a lot of foods in the “don’t eat” list and you start eating more from the “do eat” list you ..." it doesn't look like a CSS issue, more like a TinyMCE issue.

The first part, where line breaks exist, has <p> in the source code as should be. That other part without line breaks has no <p> but a lot of <div>..</div> instead.

I would try re-creating that part, perhaps in another browser. The browser has an impact on how well TinyMCE works or not. Perhaps Safari or Firefox 3.

If you're copying text from somewhere (including: from a browser window) paste into a text editor first to lose the formatting, then fomat inside the WP editor.

Or give the bold parts that should sub headlines, a "Heading 4" formatting