Don’t get hung up on calorie counting for fast days. Eat extremely little (or nothing) and don’t think about it. Eat normally/sensibly on the other days (it is not like dieting)

The 25% Calorie limit was essentially plucked from air and tested, and it worked under the conditions tested–the patients were allowed to eat all their food between 12 Noon and 2 PM, then nothing else until morning.

At least some of the benefits derive from the cumulative weekly energy restriction. If you reduce by hundreds of Calories on 2 days a week, and don’t eat them back on the feeding days, you will lose weight and your serum markers of cardiovascular risk will improve. The question is, how precisely to you have to adhere to the original research protocols to get the metabolic benefits? No one knows. Do what works for you. If you are achieving your goals with a more liberal energy allowance, good. If not, rein it in.

I started on the 5:2 plan (refuse to say diet – hate people who talk about their diets) the day after I read an article about it in the NYT in March ’13. Felt like it was magic. Down 10% of my weight in 4 months without pain. But I just read the book and found it both unnecessary (I was succeeding fine before I read it) and full of oddities. Donald, the authors never do address the obvious point that 500/600 calories is only a quarter of a minority of peoples’ daily requirement. I understand they are trying to make it simple, but again and again they repeat that you are eating a quarter of your daily caloric need. I try to keep my intake to about 400 calories on fast days, which is still over 1/4 of my daily need – about 1200 to 1300 calories (yes, I am a very small person with a light activity level). I would have felt better about the “rules” had the authors just admitted that the numbers are semi-random. The calorie counter in the book is ridiculous – what was the point of pretending a serving size is 100 g or 100 ml for every food? I guarantee that no one eats 100ml of butter for one serving (739 calories!) or for that matter, 100 ml of Coke (a mere 43 calories). The authors say they want to hear from people, so I hope they will read this and respond! And in spite of my gripes, I’m thrilled to have learned a way of taking care of my body that I believe I can maintain for life.

I agree, Christine, that that was their intent. It would be fine had they chosen more appropriate column headings than “serving size” and “calories per serving”. Well, hopefully people reading the book know that their bottle of Coke doesn’t contain only 43 calories (but I’m not sure – people can be pretty dense about these things…).

Why would you drink coke on a fast day?

I guess the previous post was about diet coke. I was wondering whether, when I drink tea, does the lactose sugar in milk on fast days cause significant insulin spikes? I’ve read that the body can’t burn fat when there is insulin in the system but I drink tea half hourly!

donald – I’m not sure where you are but you were referencing kilojoules ‘Kj’ on your initial post. The standard reference for the fast diet ‘rules’ and in the books internationally I believe, are Kcals. The 2 are different measurements of calorie content and are not interchangeable, so do be careful to take in 600 or 700 or whatever you decide Kcal rather than Kj.

Other than that, if you really want to do the science bit then go to the ‘how’ tab and calculate your individual numbers. It will give you a TDEE (the total calories you should take in on any normal day in order to maintain your current weight (your fastday amount is a quarter of that). It will also give you a BMR which is your minimum normal intake which you should never dip below on a non-fastday.

As you are not doing this for weight loss I’d take your TDEE times it by 7 to get your weekly calories for maintenance. Then I’d knock whatever your 2 fastday calories come to. Then I’d divide that number by 5 and use that as your personal TDEE. Then you would not gain or lose as long as you always remain roughly around that daily figure on your non fastdays.

Additionally – to get the optimum health benefits from the actual fasts I’d make sure that you go at least 14-16 hours between beginning your fastday and having any calorie intake whatsoever. It’s the genuine (absolutely no calorie intake whasoever) fasting period that does the IGF-1 ‘magic’ and provides the other health benefits. Say your last meal is 7p.m. the day before your ‘fastday’ – you shouldn’t eat or take in any calorific drinks before 9a.m. on your fastday at the absolute earliest (to be safe I’d say give it a good 16 hours – 11a.m. – to be sure).

Good luck with whatever you decide to do.