This is a hands-on demonstration. Try it (with adult supervision and appropriate safety precautions) and see! One gram of pecans should contain about 7 Calories, or 7000 calories, if the energy released from burning all goes into the water.
Work Step by Step
Source for calorie content: Wikipedia contributors, "Pecan," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php?title=Pecan&oldid=701881974 (accessed February 3, 2016).