Fasting in 5:2 is not really fasting ... especially if you are exercising. Monday and Thursdays I calorie count to 700. (more than the 500 everyone says because of cycling/excercise). So that's a big bowl of porridge, cup a soup at lunch time with tea being a large jacket spud with cottage cheese and a massive portion of salad and dressing
The actual recommendation is "25% of normal intake"
500/600 is a basic rule of thumb that is easy for most folks to work to, but for a very active person 25% is a better guide.
My base metabolic rate (sitting in a chair all day simply existing) is 1900 Calories
Lifestyle takes that up to around 2800.
So I target 600 knowing that if I get it a little wrong I'm still within the range.
People (including the op) seem to get hung up about the term "fasting", Don't think of it that way. The OP spoke of working to a calorie deficit over the week. That is all the 5:2 diet does - gives a calorie deficit over the week but concentrated in 2 days. With the important caveat, that anyone who is serious about losing weight transfers some of the principles to other days too and does not over indulge.
Don't call it the
Fasting Diet, call it the
2-day Calorie deficit diet!
But somehow that does not have the same attention grabbing effect of "
Fasting"
ALL weight loss diets work in the same way: Imposing or inducing a Calorie Deficit.
Eat nothing but protein and you feel fuller for longer and get bored by eating so eat less = calorie deficit
Cut out fats from your diet = calorie deficit
Exercise more, eat the same = calorie deficit.
Eat pre planned meal replacements = calorie deficit
Eat cabbage 5 times a day = calorie deficit
Count and restrict calories for every meal = calorie deficit.
It's not rocket science.
FWIW, my "Diet" has been "good" for may years. Red meat rarely. Fish at least one a week often twice. White meat regularly. Remove the chicken skin. Piles of fruit and veg every day. Veggie meals 1/2 days a week. Very rarely had a pudding. All quality ingredients from a mix of Waitrose, independent butchers and farmers markets. I'm a foodie and wanna be Master Chef so recipes and cooking were fantastic.
Problem was, I ate too much good food.
I now still eat the same good food 7 days a week, but some weeks on 2 days a week I eat less of it.