They argued that it's just a matter of time before the French-who are in fact eating more hamburgers and French fries these days-catch up with Americans,
and begin suffering the same high rates of cardiovascu-lar disease.
书中翻译:他们认为:法国人赶上美国人,开始有同样高的心血管病比率只是个时间问题-近来,法国人其实吃的更多的是汉堡包和法国油炸是食品.
书中解析是it's ....before 是强调句.我好像以前没看到这种句式而且Before在这里好像没有意思。

They argued that it's just a matter of time before the French-who are in fact eating more hamburgers and French fries these days-catch up with Americans,
and begin suffering the same high rates of cardiovascu-lar disease.
我认为这里It's...before...不大可能是强调句型，应该是一个主语从句。before后面所跟的部分是句子真正的主语，it是一个先行代词，作形式主语。