"Exercise For Weight Loss"

At least four clinical trials have demonstrated that exercise tends to suppress resting metabolic rate. In all four studies overweight participants who engaged in 300-600 calories worth of daily exercise experienced a significant drop in resting metabolism. According to Drs. Jeff Volek and Stephen Phinney, “Although genetically lean people as a group may respond differently, when overweight humans do more than one hour of endurance exercise daily, resting metabolism on average declines between 5% and 15%.” 

Commenting on the pair's findings, Dr. John Briffa points out that this down-regulating of the metabolism is probably the effect Taubes is describing. Much like what happens when caloric intake is severely restricted, "The idea that the body would down-regulate the metabolism in response to exercise makes ... intuitive sense," says Briffa. "It’s not too difficult to imagine that the body would have a similar response to increased calorie expenditure ...."

Critics of this argument would likely cite any number of studies which have reached the opposite conclusion. But as the American College of Sports Medicine explains, the best that can be said about the relationship between weight loss and exercise is that "it is reasonable to assume that persons with relatively high daily energy expenditures would be less likely to gain weight over time, compared with those who have low energy expenditures. So far, data to support this hypothesis are not particularly compelling.”

http://www.policymic.com/mobile/articles/10213/why-exercise-doesn-t-actually-help-you-lose-weight

But, say the Biggest Loser fans, doesn't exercise burn calories?  Yes, but if you are eating in such a way as to create a hormonal demand to sequester the food you eat as fat, exercise won't interrupt that cycle, and is likely to make you feel hungry.
Diet also plays a role. According to researchers at the University of California, San Francisco, people who consume a lot of easily digestible carbohydrates (most Americans) are going to be less willing to exercise because of the metabolic effects of such a diet. Energy that ends up trapped in fat cells (just one of the awesome side effects of a high-sugar diet) isn't available to fuel the rest of the body, and one of the results is lethargy. 
So, the science isn't compelling one way or the other, but experience indicates - you have to eat better, and exercise right, to have the maximum impact on body composition.

The counterpoint to this perspective will be presented tomorrow, and I'll explain why anyone who wants to shoot strait with a client should be clear that exercise alone won't fix what ails them.