And it seems the reason for her weight-loss was simply trading the elliptical for the treadmill.
The mother-of-three, 39, told People: 'I used to be more an elliptical-and-weights girl but I've started running in the last year and I hate it and love it at the same time.
Weight-loss: Twilight author Stephenie Meyer pictured in June 2010 (left) and last night at the New York premiere of The Host (right), looking several pounds lighter after taking up running
It's no surprise Mrs Meyer has lost weight. Running is considered by many fitness experts to be one of the best forms of cardio, and burns twice as many calories as walking, according to Runner's World.
Celebrity personal trainer Matt Townsend told MailOnline: 'Of all forms of cardiovascular exercise, running is by far the most effective in reaching your fat loss goals quickest and efficiently.
'From short distance sprints to long distance marathons, the benefits of running far outweigh the risks of injury. For nearly all of my fat loss clients in particular, I almost always incorporate some sort of incline treadmill or hill running for maximal caloric burn.'
Partying with the A-list: Mrs Meyer (center) with the stars of The Host, from left: Jake Abel, Diane Kruger, Saoirse Ronan and Max Irons
'She's so excited [I've started running],' the bestselling writer said. 'She wants me to run races with her now.'
Mrs Meyer, who wore a striped Kate Spade dress for the event, admitted that promoting The Host had taken its toll on her healthy lifestyle though, and she was looking forward to getting home to Arizona, where she lives with her husband Christian and their three sons.
'This tour has been awful for my diet. Really, really bad!' she said. 'I have to get home and get back to my gym.'