By Philip Scott Andrews/The New York Times – Most politicians hate loss, but not when it applies to their waistline.

Senator Claire McCaskill, Democrat of Missouri, talked to reporters about her recent weight loss Tuesday.

Senator Claire McCaskill, Democrat of Missouri, who is in a tough re-election fight, has lost 50 pounds over the last few months, largely by trimming her portions and hitting the treadmill for about two miles of fast walking on a steep incline each day, she said.

Ms. McCaskill, whose look these days is less lawmaker and more fashion magazine editor, has chronicled a bit of her new exercise regime on Twitter, where she gave a shout out to her trainer and a hint of what she has given up: “It’s official. I have divorced bread and pasta. I’m hoping someday we can be friends again.”

In a brief interview in the Capitol on Tuesday, Ms. McCaskill said her need to lose weigh was “part of being a woman in her late 50s.” “The metabolism shuts down on you, and all of a sudden you’re feeling slow and tired. And I need lots of energy and I knew I was going to need lots of energy in the next year, and I decided I needed to put the excuses aside and get more physical.”

The senator is waiting to see which Republican challenger she will face in what is certain to be one of the Democrats’ toughest re-election battles in the Senate next year. Representative Todd Akin of Missouri, John Brunner, a businessman, and Sarah Steelman, a former State Treasurer, are locked in a battle for the Republican nomination.

Asked if she was considering running a marathon someday, Ms. McCaskill glanced toward the Senate floor and said, “Isn’t this a marathon day in and day out?”