Assuming your body, with your lifestyle, requires on average 3500 kcal a day to sustain itself, and if your body can extract 3500 kcal out of the sand you produ

Assuming your body, with your lifestyle, requires on average 3500 kcal a day to sustain itself, and if your body can extract 3500 kcal out of the sand you produce, then yes, you won't lose weight. There are multiple factors that change: 1) intestines+stomach can have different absorption rates 2) food preparation can change amount of calories (cooked food simplifies calorie extraction) 3) glycemic index affects how readily cell absorb calories 4) body can only release a limited amount of energy out of fat cells per day (study seems to suggest 22kcal per day per pound of fat). Deficit beyond starts burning through other tissues than fat 5) Base metabolic rate - different weight and different lifestyle will have people have different amount of daily required calories There are many things that are affected, and it is best to calculate out yourself. How efficient is your body in absorbing calories, and how efficient is it in burning them, and then ensure you absorb less than you need to burn.