It took me two full days to recover from Monday's fast. I felt so bad that I have decided to tweak the plan a bit, and eat two 500-calorie meals on "fast days" instead of one for while. It will still be good protein and green vegetables, and given my normal daily caloric intake, I do believe that bringing myself down to 1,000 calories/day two days a week will result in a pound or so of fat loss each week.
I simply cannot feel that weak, tired, and lightheaded 4 days each week while taking care of my baby (Monday while fasting, Tuesday while recovering from Monday, Thursday while fasting, and Friday while recovering from Thursday).
Today I've had a salad made with mixed greens, turkey breast cutlets, and carrots and I'm happy to know I will have salmon and asparagus before bed. And I won't feel awful tomorrow. Perhaps my body will become adjusted to fewer calories and more hours between meals over the next several months, and then I can do the 5:2 diet as written without it being such a shock to the system.