Gary Taubes has taken on conventional wisdom by challenging the "calories in, calories out" paradigm (read all about it in his book, Why We Get Fat). His contention, basically, boils down to this: other factors, such as insulin, affect weight loss. He has taken a lot of grief for his position, but consider a new piece of evidence:
One research study now considers that tonsillectomies might be an obesity risk factor. In this review study, 1,549 children who had a tonsillectomy were followed for up to seven years. They were weighed pre- and post-surgery and thereafter for the duration of the study, and were compared to a control group. The children with tonsillectomies were significantly heavier than the control group and "the gain in height was not commensurate with the gain in weight." The authors conclude that the tonsillectomy may be an obesity risk factor.
How does a tonsillectomy lead to obesity? The authors don't say, but they did notice the weight gain. This may be one of these "other" factors that contribute to obesity, not merely "calories in, calories out."
Along the same lines, another author, Michael R. Eades, M.D., suggests that the "quality" of calories, not just the quantity, counts. He described two very different studies of people on a 1,500 calorie diet. In one study, the subjects had to be locked up to prevent them from eating additional calories. In the other, the subjects ate as much as they wanted, until they were full. There are some astonishing differences between the two studies.