Research has demonstrated that there is about about a 15% base difference between people with &quot;slow&quot; metabolisms and &quot;fast&quot; metabolisms.  In addition, the composition of your gut microbiota significantly impact how efficient you are at extracting energy from the food you eat.  To top it all off, some people notice a larger&#x2F;more immediate reduction in BMR when they reduce calories than others.<p>At the end of the day calories in&#x2F;out is still correct.  It is just more complicated than how much food you eat and how much activity you engage in.