How to remove your SparkPeople account
From their FAQ (https://www.sparkpeople.com/community/help_answer.asp?id=14)
Click on ‘Start’ in the top left corner of the screen. You’ll now see your Start page.
Click on the ‘Account/E-Mail Preferences’ link in the upper left corner of the page. (Note: Your Account/E-Mail Preferences link can also be found by rolling your mouse over your username in the upper right corner of the page and selecting Account/E-Mail Preferences in that menu.)
Scroll down the page to the ‘Close Account’ section.
Click on ‘Close Your Account.’
Click on ‘Yes, I Am Sure.’
Your account will now be closed.
Helpful Trick: Removing online data
Publicly visible text/images often aren’t properly removed even when you succeed in removing an account. Try editing or removing them manually before removing the account itself. If you’re unsure what happens to your tracks: this can be found mostly in the Terms of Service/Privacy Policy; otherwise you can always contact SparkPeople and ask personally. By the way, removal requests don’t necessarily mean your data will actually be removed (e.g. due to legal obligations).
Helpful Trick: Remove third-party logins
If you signed up for SparkPeople using a third-party login such as Facebook or Twitter, you probably want to revoke all access from SparkPeople. Click here to find out how.