>Alternate day fasting (ADF) is a subtype of intermittent fasting and is defined as a continuous sequence of a fast day (100% energy restriction, zero calories) and a feed day (ad libitum food consumption), resulting in roughly 36-h fasting periods.

I'm interested. So on fasting days you consume water and absolutely nothing else? Or maybe tea or black coffee? I suppose there are some other zero calorie things that can be consumed, but I am betting that zero calorie sugar substitutes could be problematic because they can still cause an insulin response.

[Edit] here it is, I guessed right about the diet drinks.

>ADF group: Subjects are asked to refrain from eating on the fast days and to eat ad libitum on the days between the fast days. On fasting days, subjects are only allowed to consume water, flavoured carbonated water, unsweetened tea or coffee. Furthermore, diet sodas or so called “calorie-free” meals or beverages are restricted.