Human bodies can vary when it comes to efficiency of converting food to energy. I do not doubt this, but is there any evidence that these variances are signifi

Human bodies can vary when it comes to efficiency of converting food to energy. I do not doubt this, but is there any evidence that these variances are significant? Treating human bodies as 100% efficient food to energy converters is useful for practical reasoning about weight loss; unless these factors are significant, focusing on macronutrients, genetics, or the "hormonal situation" is just getting lost in the weeds.