I read a great article from New Scientist the other day detailing why the calories in / calories out equation is flawed (at least on the calories out side): http://clicks.aweber.com/y/ct/?l=CV_1u&m=nAujoXKYQ6icE4Y&b=yX7R7KKbbS_FwzgpL1pDqA For those of you who aren't a subscriber - I'll summarise the scientific findings from the report: 1. Firstly - exercise is extremely important for staying healthy. This quote from the report sums it up nicely "...Being active improves overall health, mobility and brain function, and reduces the risk for many chronic conditions including Alzheimer’s disease..." 2. When it comes to weight loss - exercise is not very effective past an initial calorie burn point. "...those who were moderately active used up about 200 more calories per day than sedentary people, but after that, calorie burning plateaued. Those who exercised every day didn’t burn any more than those who worked out a few times a week...". It turns out that your body is very good at regulating your "resting metabolism" after excessive exercise. The theory is that your body has learned to do this to conserve your mass in case you need it for future leaner times. 3. Exercise is good for maintaining weight loss after a period of dieting and preventing weight gain. "...exercise does still have a place in the weight-loss journey: once you lose weight, it can help prevent the common problem of putting it back on...An analysis of contestants on The Biggest Loser, a TV weight-loss show, found that during the 30-week competition, weight loss and amount of exercise weren’t correlated. However, six years later, those who increased physical activity the most regained the least weight or kept it off..." 4. Diet is far more important than exercise if you are trying to lose weight. It turns out the calories in / calories out equation only really holds true on the left side! "...Ultimately, it is hard to avoid the conclusion that, for many people, diet offers greater potential than exercise to get the calorie equation working more in your favour..."