I've been doing the "8 Minutes in the Morning" exercise routine, plus cardio, for seven weeks now. My diet has been mediocre -- I was eating less for about five of those weeks. This last week I've eaten quite a lot of junk food.
My weight, for the entire last five weeks, has held steady at 160.
So, yes. If I actually care about my weight (it is not clear to me that I do -- it's not as if I dislike the way I look or feel now), I need to change my diet. At minimum, eat less of what I'm eating now. I am unenthused about doing so.
I have no good explanation for why my mind thinks regular exercise is reasonable but eating well is too much work. Maybe it's because I see eating foods I enjoy as a positive good that I will get less of, whereas exercising for a little while is not that much inferior to sitting in front of my computer for the same period of time. So it's not so much that eating less junk is too much work as that it's too much sacrifice. I'll make an effort in the coming week anyway and see if I make any progress.