A human walking is absurdly efficient, as anyone who's ever tried to outrun a bad diet can tell you. Running or walking a mile burns ~100 extra calories relative to sitting on your couch. Unless you're putting active effort into not doing so, most diets fluctuate by far more than that.
Even if we count the cost of the co2 emissions: it probably takes more petroleum products to grow the food for the walking delivery workers than it takes to fuel the delivery truck.
