Welcome to the 5:2 forums, fastandfree. When I first read Moseley’s book it was 500 calories for fast days (FD). I think he later upped the calories for people who couldn’t manage only 500. Even with 500, weight loss can be rather slow, about a pound per week is average. And when you get close to your goal it can be even slower. I think I might have become discouraged by the speed of weight loss if it had been too slow. And I didn’t want to count calories on NFD’s so the 500 calories worked for me. I figure it’s just a small amount of food to hold you over.

I’ve been doing 5:2 for maintenance for the last 9 months and still use 500 calories. I eat more on NFD than I did while I was losing. It works. You get so used to FD that they become a habit. I eat pretty much the same things every FD because it’s easier and they are foods that are easy to keep on hand. I think a lot of people here do it that way. These are the foods I choose from, in a combination to come up to 500 calories:

Canned salmon with a sprinkle of lemon juice 160 cals
12 ounces of broccoli or califlower, from frozen bag 100 calories
A piece of fruit like banana, apple, pear, peach 70 – 120 cals
Oatmeal 1/2 cup dry,
Soup, canned or homemade, around 200 calories for the can
Miso soup around 60 plus any vegetables added