Hello M4YG – I am sure there are much more experienced qualified people on here who will answer you but I wanted to say Hi as I turn 40 in November and that is really what has spurred me on to do this and from your name sound like you are in the same boat? My understanding is that the 500 for women/600 for men is an approximation – I guess that even at 500 calories for your fast days it would still work (albeit very slowly) as it is much less that you would usually eat and it should be achievable as it means you can have something like porridge and fruit for breakfast and chicken or fish with salad or hot vegetables for your evening meal. But I think that for weight loss you should try a quarter of your usual calories if possible so that might mean just one meal a day for you or fruit only for breakfast – you have to be really careful and count every calorie – especially if you drink milk with your coffee and tea? I am on week 4 now and in my first week I had calorie free drinks only on my fast days – black coffee and herbal teas, sparkling water with lemons and limes squeezed in and diet coke. I lost 4 pounds. Weeks 2 and 3 I ate around 500 calories – no weight loss although no weight gain so it may be that I am losing bits of a pound (my scales are not v accurate). SO this week I am back to calorie free drinks again only to see what happens. There is loads of great advice out there so I would recommend looking through a few of the forums and then try it out ans see what works for you – good luck!!