You don't even have to put in THAT much effort to see a significant change (depending on starting mass). Try the calorie calculator here. (http://goo.gl/XBPt) I went from 245 to 220lbs without much drama just by making small changes and integrating physical movement better into my life.
If you are eating a 4000-kcal daily diet regularly, cutting your intake in half isn't going to help you lose weight... it's going to help you quit dieting because dropping half your intake is extremely difficult. You can't tell your stretched out stomach, "Hey, so please stop telling me you're hungry."
Cut out one bad thing a week. If you're a total red-meat head and think that no meal is a meal without fried beef, then that may be a problem. Make the switch from red meat to chicken, pork, and fish. If you're a fried-food maniac, cut out fried meats and potatoes. If you're eating fast food for more than 4 meals a week (schedules are a pain, I know), choose a better fast food option. Subway is not a bastion of extreme healthiness, but a footlong turkey on wheat will do significantly less damage than a burger and fries from Five Guys.
And cut out the soda. All of it. Iced tea, water-- almost anything else. But start weening yourself off of it. Still want the fizz? Buy 2-liters of club soda, juice a lime, a lemon, an orange, or a grapefruit at home, throw the juice on ice and top off wit the club soda. BAM-- a non-ultra sweet soda.
If you want to lose weight and stick to a better diet (but not go on "a diet"), you have to make small changes. You have to create a new normal. Do too much at once, and you're dooming yourself to failure.