I started HIIT yesterday because what I was doing before absolutely wasn't working. Six days a week I would do 100 minutes of cardio, a combination of erging (rowing machine), running, stair-stepping, and using the elliptical machine. I also only aimed to eat 700-1200 calories a day (terrible, I know now thanks to John's website)! Despite this, I had a very difficult time losing weight. For the last week I've been eating 1500 calories and backing off the cardio and my weight is finally coming down, which seems counterintuitive.

Why is it that working out LESS has caused me to lose MORE weight?

I am not used to doing only 25 minutes of cardio every other day. I used to run marathons, so I feel antsy doing so little. What is the most cardio I can do and still lose fat efficiently? Is walking three miles better than running it if I don't want to lose muscle and keep my metabolism high?

Thanks for your help! :)

Female
5'6" (168 cm)
130 lbs (69 kg)
18.5% body fat
20 years old

Well, the reason for weight loss (this is my guess) is due to the increase in calories. It seems as thought starving yourself should cause you to lose more weight. Well, that's incorrect. By eating so little, your body starts thinking it is starving and therefore your metabolism slows down quite a bit to counteract. You need to eat enough (and often enough, 5-7 meals/day) so that your metabolism stays at its peak throughout the day, but not enough that you surpass the number of calories you burn each day.

I personally eat about 11x my body weight in calories per day and do cardio (HIIT) 5-6 days a week for 20-30 minutes depending if I lifted first or not. It may be excessive, I am not sure. I am just trying to lose the last couple pounds of body fat for complete visible definition.