Sen. Claire McCaskill (D-Mo.) said she might be motivated to "be more disciplined" if she talks publicly about how she feels about her weight.

"I'm tired of looking and feeling fat. Maybe talking about it publicly will keep me on track as I try to be more disciplined. Off to the gym," McCaskill tweeted Thursday.

The tweet is an extremely rare view into McCaskill's personal thoughts (or the personal thoughts of any lawmaker, for that matter). Legislators often use Twitter to highlight press releases, cheer sports teams or quickly voice policy positions.

McCaskill has some company in using Twitter as a weight-loss tool; some tweeters have used the social media site as a sort of daily food and/or exercise diary.

Newark, N.J., Mayor Cory Booker, for one, has been very public about his attempt to lose weight. In early January, in an effort to “lead by example,” he wrote an essay on his Facebook page about his effort to get fit. He set a weight-loss goal for himself.

"I am making a public commitment today that by my birthday on April 27th I will be below 240 lbs and still making progress towards my healthy goal weight of 230 lbs," Booker wrote.

Today, Booker sends tweets, and retweets, of encouragement to Twitter users who have shared their exercise regimens with him.

Others have followed a public get-fit regimen, including tweeting what they ate or weighed each day, as New York Times media reporter Brian Stelter did.

--Kelly Mae Ross contributed.

--This story was updated at 2:01 p.m.