33 lbs = 33 minutes?

I've never done a full marathon, at least not in a competition. I've done a few half-marathons and also some runs ranging from 20 to 33 km.  The plan is to do a full marathon next autumn. Now, as I have mentioned before I'm a little bit overweight. I love my steak and a good desert, and when it comes to my diet, changing old habits has never been an option. What I could gain in terms of improved times/performance is simply not worth the sacrifice. Or so I thought, until a few days ago when I met guy who insisted that in terms of marathon time, one pound equals one minute. This means that each pound you carry, in excess of optimum body weight, slows you down one minute for the duration of a marathon. I understand that I'm some 33 pounds over my optimum weight. That's 33 minutes. More than half an hour. I never imagined it would be THAT much. I need to do some research to find out whether this actually true, but I must admit it really gives me something to chew on, while I eat my French-fries.