It usually takes about 2-3 weeks until you feel the strength really kick in. Around the 3 week mark I start to sweat a lot more just sitting around too. So about 3 weeks for the full effects t hit you. I do know that your metabolic rate starts to increase around the 3-4 day. I used to run a metabolic rate testing program at Ballys' and I used to check myself out all the time. You can expevt your resting metabolic rate to go up as much as 25% from your norm. In other words, you will need 25% more calories to maintain your weight at total rest.