In reply to Christy.

That's a great question Christy!

Keeping a long fast is good but should not deprive you of calories and nutrients. If you want to make your fasts work long-term, you should start out with ~16 hour fasts and then push to 18 or so once you're comfortable and your body has gotten used to it after a few weeks. The reason I say this is because your body is used to a certain schedule and breaking that schedule will make you perform worse overall without slowly adapting to it. Your energy levels will be low which will affect your thought processes and overall productivity (and chances to succeed). Remember, the goal is to be healthier and sharper - not the other way around.

Regarding not consuming your calories: it is simply not good because that's malnutrition. Intermittent fasting is a change in schedule, not diet.

Schedule-wise: Eating all your calories in 1 meal is unrealistic. Eating all your calories in 2 meals is unlikely (at first). Try to have an 8 hour window with 2 big meals and a small 3rd meal and then slowly transition to 2 meals by increasing the size of the bigger meals and cutting out the smaller one. Do all of this gradually. There's no reason to rush!