 Most would be offended if a person refused to have a meal with them, if one insists that they are satisfied, the best approach is to eat very little.Complete refusal to eat their food might give them a picture that you are stingy so you yourself want them also to refuse to eat when they visit you or you suspect that they may have included medicine in the food "(Ukukutegha)".It is cultural to quickly prepare "ubughali", that is thick porridge made from maize flour eaten together withand  relish, for a visitor so that they should replenish the energy.