Whenever I hear something that's unbelievable, I dig deeper.
The nutrition professor in question wondered what would happen if he limited his diet to junk food and a few serving of canned vegetables. So as a part of a health experiment on himself, he limited his diet to 1800 calories a day (from junk food) and maintained his current level of activity. Keep in mind that the average man needs about 2500 calories a day.
Operating on a daily deficit of 700 calories a day, at the end of his experiment the net result was weight loss. As a bonus, his LDL (bad cholesterol) was lower and HDL (good cholesterol) was higher than when he began the experiment.
I guess the moral of this story is three-fold:
1. If you want to lose weight, the quantity of calories matters more than the quality of the calories you consume.
2. Maintain or increase physical activity (burn the calories you eat)
3. If something sounds too good to be true, it probably is. In other words, you'll never lose weight eating junk food unless you drastically limit how much you eat. (See #1)