I did a stepwise regrssion analysis to predict energy expenditure using the variables, height, weight, age, gender and energy intake. The final model contains the variables gender and weight. Now does this final model take into account gender by weight interaction? Or do I have to construct a new equation from this final model, that will accomodate interaction?
Stepwise regression has a number of bad qualities (just look e.g. here or here and this is one of them. With only 5 variables (plus one interaction), unless your sample size is small you can include all the IVs. Why would you do this?
1) It is clear, even to a non-expert, that all your potential IVs are included for strong theoretical reasons. Finding that one of them was not related to energy expenditure would be remarkable. In fact, it would be more remarkable than finding that all of them were related.
2) Even if a variable is not significant and even if its coefficient is small, it might affect the relationship between the DV and other IVs.