The easiest way is to read the label on a bag of soy flour purchased in a store. [at least in US stores]
Important note, though:
1 food calorie = 1000 thermochemical calories = 4184 Joules
Food calories are sometimes called 'large' calories.
I have a bag of ordinary wheat flour that contains 400 food calories per 4 oz. portion. Thus, 1600 Kcal/lb = 6.694 MJ/lb = 14.7 MJ/Kg = 14.7 KJ/g