I found a way to get shredded very fast.
Start with the Zen deck so you can use meditate and yoga to draw cards. After the first day, remove a workout card that you don't want and try to get pre-workout. After you get it, try and get something that boosts gain%. Once you do, try and keep drawing cards until you can only draw meditate/yoga and pre-workout. Use the pre-workout first, then meditate/yoga for infinite stamina. Get as much as you want. Do the same with a card that boosts gain%. After that, you can use a workout card and get a lot of gains.
I'm calling it gainsplosion.