Exercise -- by itself -- "is pretty useless for weight loss" because people who exercise more also tend to eat more:
[W]orking out can have a significant effect on appetite. The mechanisms that control appetite and energy balance in the human body are elegantly calibrated. “The body aims for homeostasis,” Braun says. It likes to remain at whatever weight it’s used to. So even small changes in energy balance can produce rapid changes in certain hormones associated with appetite, particularly acylated ghrelin, which is known to increase the desire for food, as well as insulin and leptin, hormones that affect how the body burns fuel.However, women's bodies "seem to react differently than men’s bodies to the metabolic effects of exercise":
In one study presented last year at the annual conference of the American College of Sports Medicine, when healthy young men ran for an hour and a half on a treadmill at a fairly high intensity, their blood concentrations of acylated ghrelin fell, and food held little appeal for the rest of that day. Exercise blunted their appetites. A study that Braun oversaw and that was published last year by The American Journal of Physiology had a slightly different outcome. In it, 18 overweight men and women walked on treadmills in multiple sessions while either eating enough that day to replace the calories burned during exercise or not. Afterward, the men displayed little or no changes in their energy-regulating hormones or their appetites, much as in the other study. But the women uniformly had increased blood concentrations of acylated ghrelin and decreased concentrations of insulin after the sessions in which they had eaten less than they had burned. Their bodies were directing them to replace the lost calories. In physiological terms, the results “are consistent with the paradigm that mechanisms to maintain body fat are more effective in women,” Braun and his colleagues wrote. In practical terms, the results are scientific proof that life is unfair. Female bodies, inspired almost certainly “by a biological need to maintain energy stores for reproduction,” Braun says, fight hard to hold on to every ounce of fat. Exercise for many women (and for some men) increases the desire to eat.But there's a silver lining. Women who reported exercising an hour a day -- granted, still more than most people would prefer to do -- tended to keep from gaining weight in their middle age.
Also, "if you can somehow pry off the pounds, exercise may be the most important element in keeping the weight off." Studies show that those who steadfastly stuck to their exercise routines " regained less weight than those who didn’t exercise and, even more striking, did not regain weight around their middles. [On the other hand, t]he women who didn’t exercise regained their weight and preferentially packed on these new pounds around their abdomens."
In a completed but unpublished study conducted in his energy-metabolism lab, Braun and his colleagues had a group of volunteers spend an entire day sitting. If they needed to visit the bathroom or any other location, they spun over in a wheelchair. Meanwhile, in a second session, the same volunteers stood all day, “not doing anything in particular,” Braun says, “just standing.” The difference in energy expenditure was remarkable, representing “hundreds of calories,” Braun says, but with no increase among the upright in their blood levels of ghrelin or other appetite hormones. Standing, for both men and women, burned multiple calories but did not ignite hunger. One thing is going to become clear in the coming years, Braun says: if you want to lose weight, you don’t necessarily have to go for a long run. “Just get rid of your chair.”A few weeks ago, I abandoned by office chair altogether and raised my computer monitor so that I could comfortably use it standing up. I'd intended to try it out for awhile to see if I liked it, but now, it looks like my new set-up's going to be permanent.