The 5:2 fasting in the Michael Mosley sense is not intended for weight loss, but for a more healthy living.
But of course, you can easily use it to gain some weight loss advantages too. I do this on a regular basis, and it works great.
I would suggest that you go with two days of 600 calories (4-500 if you're female), and simply go with your regular RDI on the other days. You will feel AWESOME - the "fasting days" will do that for you - and it will help speed up weight loss.
Initially, doing days of 600 (or less) calories can be quite a challenge. However, it gets a LOT easier as you get your grip on this.
Today, I have scheduled less than 200 calories for the entire day. No biggie.
"Losing weight is never about eating as little as possible"
"You wouldn't worry so much about what others think of you if you realized how seldom they do.
― Eleanor Roosevelt
"Do. Or do not. There is no trying."
- Master Yoda.
From October 4th 2010 to April 3rd 2012 I lost half my body weight - 80 kilos/170 lbs. Since then, I have had two cosmetic surgeries to remove excess skin. I have now quadrupled my strength, gained several kilos in muscle mass, and today I focus on building muscle, optimizing my diet, and living healthy. I am stronger, healthier, thinner, happier!