The calorie value is an absolute upper bound.  But some people have a gut flora that helps them extract more of those calories than the regular population.  And some people have a gut flora that helps them not extract some of those calories.<p>And since gut flora can change over time a person eating 2000 might be maintaining weight one year but gaining weight the next year with no change in food intake.<p>I agree that people who say &quot;I eat very little and I&#x27;m not losing weight&quot; are mistaken.