Hi and welcome:

Let’s see, two 36 hour periods (72 hours) with 1000 calories eaten v. three 24 hour periods (72 hours) with 0 calories.

It would seem you would eat about 1000 fewer calories with the three 0 calorie fasts (assuming you did not compensate by eating more during the time you could eat).

But why? It is harder, perhaps more bothersome from a lifestyle point of view, and an additional 1000 calories a week deficit adds only an additional 4.6 ounce loss for the week to the standard 5:2 loss.

You will have to determine if doing three 24 hour fasts is worth an additional 4.6 ounce loss.

Good Luck!