Welcome to the 5:2 Fasting group! If you haven't already, please take time to look at the Michael Mosely documentary on intermittent fasting that can be found under the announcements on the group's main page. It will give you lots of great information about the basics of the plan.

To answer your question, there are only two hard and fast rules to the plan (which is why we like it so much!): 1. Eat 500 cals on two days of the week and 2. Eat your Total Daily Energy Expenditure calories on the other five days. Simple as that. What you eat and how you eat those calories is totally up to you.

Since you are new, I recommend two things - to log what you eat to make sure you are not seriously over or under your daily calorie goals, and to start with what seems intuitive to you. For example, if you are not normally a breakfast eater you may want to start eating later in the day. If normally, you can't live without breakfast you may want to spread your calories over the day to so as to start the day with breakfast. One last tip, make sure you drink plenty of fluids on the fast days. It will help with hunger and headaches, should you have them.

We wish you well as you begin this journey. Feel free to post additional questions as they come up.

Personally, I try to save all my fasting calories for my evening meal to give me a bigger fat loss window.

According to Brad Pilon "Fat loss starts happening at about 12 to 13 hours and plateaus around 18 hours,"

I've always found fasting easier this way but can totally understand people who can't manage the day without anything. Plenty of water is great for keeping hunger at bay.

Experiment!
I found I can easily skip breakfast without any hunger issues.
A small lunch (c. 40%) and a slightly bigger dinner (c. 60%) works best for me.

I was eating around 1pm and then eating dinner, but the last two times I've eaten JUST dinner and I've lost more weight this way. Not sure if there was a correlation there, but now I'm aiming to fast all day (drinking water and tea) and eating all 500 calories for dinner.

The headaches if similar to rolling migraine AND when eating low carb on FD, is your body's reaction to not getting the amount of carbs it's used to have. Supply with electrolytes, might help. Google symptoms of Atkins flu, if you're interested.

I had the headaches for about 2 weeks, then it was gone. But I took a choice and went LCHF too. I figured might as well, since FD are low carb...

I don't know if they keep coming back if you return to "high carb" diet on TDEE days on a regular basis. Someone else might have experience and can give their opinion.

I had headaches for the first few fasts but now am no longer troubled by them. I think at first your brain plays tricks on you to try to get you to stick to the old ways; but once you train it to realise that the only negative consequence of a fast day is a rumbly tummy, it settles down. Very first fast I had 100 cals of carbs as a late lunch and felt really hungry for the rest of the day; second fast day I had 100 cals of low carb protein shake instead which I found much better; gradually I extended my FDs, so now save all my calories for an evening meal. Hope you decide to join us!