Hi Fit:

You have every right to be confused. The popularity of 5:2 along with new research has brought the term ‘fasting’ to many people’s awareness, but with that popularity comes the many different meanings of the word and other things totally unrelated to weight loss.

The 5:2 book is called Fast Diet, and the book apparently uses the term ‘fast’ liberally, as in fast days. However, the book actually has you eating on ‘fast’ days. The definition of ‘fast’ that covers this concept is “to eat only sparingly”.

Another, more commonly recognized definition of ‘fast’ is to eat nothing at all. But then you get into the concept of time frames – if you eat six meals a day, then you actually fast between every meal and overnight when you sleep (note the term ‘breakfast’).

In addition to the confusion caused by trying to determine what a ‘fast’ is, there is the additional confusion that comes with trying to combine a weight loss diet with a life extension diet. The Fast Diet book thoroughly helped the confusion along by claiming that if you do 5:2, in addition to losing weight you might gain ‘other health benefits’. The confusion results from whether the ‘other health benefits’ might come from ‘fasting’ or ‘calorie restriction’. Those terms can be, but are not necessarily the same. For instance, people can go for 24 hours without eating, but still eat enough at other times to maintain or gain weight, in which case there would be no calorie restriction – at least for a long enough time to do any good given the current state of research.

Many believe the ‘other health benefits’ come from ‘not eating’, but then the debate starts on ‘not eating for how long’? Some believe that not eating for a few consecutive hours a day will lead to ‘other health benefits’, and tout 16:8 or 19:5 as being helpful. The research currently shows you need to not eat for 4 or 5 days several times a year for the ‘other health benefits’ to kick in. There is no current research showing short term fasting, measured in hours, brings with it any ‘other health benefits’ (including additional or faster weight loss, if you think weight loss is a health benefit).

So people come to 5:2 to lose weight and are immediately thrown into debates on how much to eat and when to eat, with all sorts of claims being made about why you should eat one way or another. Some newbies throw up their hands and go away, often after trying one or more of the ‘different approaches to IF’ and finding they don’t help with weight loss, and some stick around long enough to sort through all of the clutter and lose some weight.

The fact is that weight loss is not rocket science. It simply requires caloric reduction. 5:2 provides that caloric reduction if done properly – 5/600 cal. on two diet days each week, and TDEE or under on the remaining five non-diet days each week. You do not need watches to measure how long it has been since you last ate or can eat again. There are no special foods you must or can’t eat before you can lose weight. You simply have to eat less of whatever you have been eating and if you eat enough less, you will lose weight. The science behind 5:2 is solid. There is much speculation and hope and hype and misinformation about other methods of losing weight and gaining ‘other health benefits’, but no scientific support at this time.

My advice is to just do the basic 5:2 for one or two months, focusing on the calories you are eating on your diet and non-diet days and not worrying about when you eat your calories or what you are eating. Then adjust your caloric intake accordingly if you are either losing too fast or too slow for your liking.

Here are some tips as you go forward with 5:2: https://thefastdiet.co.uk/forums/topic/the-basics-for-newbies-your-questions-answered/.

The less you eat, the more you lose.

Good Luck!