Hunkering down with a Sudoku puzzle could help you shed some pounds. Tim Forrester, the man behind brain training website cannyminds.com, says mental exercise doubles as real exercise, with the body burning 90 calories for every hour spent working on crossword puzzles or brain teasers. A passive brain requires 0.1 calories a minute to survive, Forrester tells the Daily Telegraph, while an active brain burns 1.5 a minute. See, that gym membership was a waste of time. (More puzzles stories.)