Google Analytics doesn't have any way to report on keyword trends. The main way that Google Analytics gets its data is from the visitors to your website. That doesn't provide any insight into whether there are more people like the visitors you get now or not.
You can hook up Google Analytics to Google Webmaster Tools. The data in webmaster tools does provide some additional insight for you. It will show your impressions in the Google search results over time and an average ranking for each of your top search terms. Unfortunately there is no way to see how ranking has changed over time in this tool.
Impressions going up over time from Google Webmaster Tools would answer the question for you, but only if you know you have been on page 1 of the search results for that term. Impressions also go up when you gain first page rankings for a term.
I would use Google Trends to answer this question. Google Trends lets you see traffic over time when you put in search terms. Unfortunately, there is no way to hook that data into Google Analytics.