500 calories is just a rule of thumb. A better rule is 25% of what you need to maintain your weight, which could be higher with your exercise and muscle and metabolism. I wouldn’t worry too much about going over, but there are two potential problems. One is that you won’t lose weight because your overall calorie intake over the week is too high. The other is that you won’t get as much health benefits as you would if you ate less on fast days.

I would think that people vary greatly in how easily they enter the “fasting state” or repair mode, as Dr. Longo referred to it on the program, but I would guess that if you’re losing weight, then you’re also fasting enough. Fasting gets easier with practice too, so if you find it hard, just start out slowly.

hi jc, I have an underactive thyroid too, on 150mcg of thyroxine. I have battled so much with my weight, buti firmly believe the 5:2 really is the way forward. I have lost 10lbs in three weeks, nearly 3″ off my waist and hips, and I feel good. And i have more energy than I have had in a long time.

So go for it, if you can keep to 500cals it is best, you can eat normally the other 5 days but the great thing about this diet is the flexibility.