Body fat loss and compensatory mechanisms in response to different doses of aerobic exercise—a randomized controlled trial in overweight sedentary males
In conclusion, a similar body fat loss was obtained regardless of exercise dose. A moderate dose of exercise induced a markedly greater than expected negative energy balance, while a higher dose induced a small but quantifiable degree of compensation.
Although well recognized as an important means for weight loss maintenance (9), the role of habitual endurance training in weight loss is scrutinized, and it has been suggested that exercise leads to compensatory responses. In the current study, we show that despite that one group undertook twice the amount of endurance training, the reduction in body weight and, more importantly, in body fat was the same as the weight loss and was equal among the two groups (a healthy weight loss). Surprisingly, the reduction with the moderate-dose exercise was far greater than what could be explained by the increased energy expenditure from the training itself (no compensation)
So the idea is that there are some sort of compensatory mechanisms that are initiated in response to excessive exercise. The body takes it as a signal to hold onto rather than burn body fat....Moderate exercise is better though and doesn't induce some reactions.
There is a very good analysis and commentary of this study over at Greatist :