When I was into high-intensity circuit weight training on top of post-workout low-intensity cardio, I lost four pounds in my first two weeks before regaining it back over the next couple of months. This was me burning a crap-load of fat and filling in the new weight with muscle. My metabolism skyrocketed and every day I was eating a big breakfast, two lunches, and two dinners, with snacks mixed in (God, I was so hungry). I didn't maintain this because my meal planning sucked. But if I stuck to this routine, I would have been a lean machine within 6 months to a year. Even though I was eating
more than I ever had in my life... even as a teenager. And the cool thing about circuit training... I only needed to do two workouts per week... and the sessions were under 45 minutes each (cardio not included).
I don't recommend only cardio. All this does is burn the majority of calories during the session. Weight training and even interval cardio mixed in will burn hundreds more calories per week as you become a metabolic machine around the clock.
The principles, as always: eat properly, train hard, rest adequately. The training part is easiest and takes the least amount of time. Get this into perspective, balance things properly, and you will be successful.
And, yeah, lose the beer.
[Editor's note: Man, I should start that routine again.
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