The Ibn Ezra suggests that Isaac was poor and therefore Esau was no longer interested in his birthright or inheritance. He cites Isaac asking for a meal before blessing his son as an example of his impoverished state. The Ramban argues vigorously against this position and connects the request for a good meal with the efficacy of the blessing. He explains that when a person is in a good mood and feels gratitude to the one he's blessing then the blessing is more effective and this is why Isaac requested a meal before blessing his son.