You can do both types of exercise for each of the three days, or just one of them. Then, when you’re on your 4 days off the diet, you can do both cardio and weight training, or perhaps lengthen the time you do either one of them by up to 45-60 minutes. You can also alternate days- doing cardio one day and strength training the next. This way you get the benefits of each, but only focus on one at a time.
I used to be 100 pounds heavier than I am now. My eating habits were out of control and pretty much the epitome of mindless. I am A.D.D., I have two kids under four, and I work full time, so eating without constant distractions just doesn't happen. But over the years I’ve learned what it takes for me to lose my weight... and most importantly, keep it off.