The FastDay Forum

5:2 Diet 'Rules' & Variations

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Hi! I'm a new guy here. I just finished my third week of 5:2 for a total of 6 fasts so far! Two of my fasting days have been with zero calories, while drinking plenty of water. For me, this wasn't much harder than getting by with the 600 calories, but I did it just to see what it was like.

Most fasts I've ever heard of prior to IF, were called "water" fasts. (I've heard of juice fasting too) Its obvious that the 600 calorie allowance makes the fast much more tolerable, but is that like using training wheels on a bike?

Will my benefits be greater if I eat and drink nothing but water instead of the 600 calories? Since it wasn't that hard, its certainly doable for me, unless there are any glaring reasons why the 600 is superior?

Height 6'5"
Starting weight 286.
Current weight 275.
6 days fasted with very little exercise.
Its logical to expect the additional weight loss as boboff has pointed out (because 1200 calories saved in a week is pretty much 1/3 lb body weight), but there are other considerations:
  • Effect on your metabolism of the more extreme fast - might slow things down by more or for longer, and this might mean less extra weight loss than you might expect (but lower metabolism might bring other health benefits)
  • Dr Longo and Dr Mattson (who both appeared in the original Horizon programme) both feel that a longer fasting period will confer more benefits, the one looking at it from the point of view of lowered IGF-1 and improved cancer resistance/recovery and the other for improved brain function, release of BDNF and resistance to dementia. See the posting here. Although Dr Longo favours less frequent but longer fasts under supervision (and a low-protein largely vegan diet).
  • A question has been raised about loss of muscle-mass on a total fast, because the lack of protein intake means your body runs out of essential amino acids. There was a topic about this here, jury still seems to be out on this one - Dr M seems to have an open mind, but Brad Pilon thinks it is tosh.
  • Few other people are doing this, and certainly Dr M would not advise it... You are out on a limb here (hopefully not a muscle-wasted one :smile: )
I tried it for two or three fasts, and to be honest it was really hard work, and for the sake of such a small amount of weight, wasn't worth it, and in my head it was just showing off to my OH who couldn't do it, plus it made eating the next day even harder.
There is also a greater risk of over eating when you do break your fast the next morning so you would need to monitor that.

Personally because my single meal on the fast day consists of mostly vegetables I feel the two fast day meals are my healthiest meals of the week so I'd be unwilling to give them up.

Reductions in thyroid function have been seen as early as 24 hours into a fast so there is a small risk that you might cause a fall in thyroid function and so a reduced metabolic rate.

But, on the other hand, if you find it easier why not? You can always change...that's the beauty of this WOL, you can change it to fit your circumstances.
Alternate day water fasters showed no significant resting metabolic rate reduction after 3 weeks ADF ... nsion.html

The apparent 90 calorie per day reduction in mean RMR was not statistically significant, and some decline in FFM would be expected to give a reduction in RMR.
But there is evidence to suggest that your health benefits will be better if you have 0 cals for the 24hr fast (like Brad Pilon recommends). This is backed up by support from researchers such as Fontana and Mattson (see ... the-horns/ )

And metabolism is not affected in the way dominic suggests. Yes, when you eat the thermic affect of food causes a slight metabolism raise for a few hours. The idea, though, that your metabolism will flat-line because you don't eat for 24 hours is not evidence based at all - it is a myth perpeturated by the "starvation mode" fallacy.

The only research I know of that showed a drop in metabolism from fasting occurred after 60 hours of not eating. Other studies show metabolic rate is not impacted until 72-96 hours have gone by without eating.

In fact, studies show that after 36-48hrs of not eating there is actually a raise in metabolic rate (3.6% - 10%). Not that I am going to try going for that long - 24hrs is enough for me.
Just remember that studies report means and medians but people form a range. Some people have shown a metabolic slow down as early as 24 hours into a fast, but the average was for there not to be. It's like winning the could be you! (but it probably won't). Many of us here fast for 24 hours...the question is whether to extend it to 36?
I have been doing 30 to 36hr ,nearly 0 calories fast days for 3 weeks now. I start the diet after dinner the night before diet day, usually about 7pm and finish at breakfast at 8am the day after diet day.
Its not completely 0 calories as I have tea and coffee with a little milk during the day.
The reason I tried this fast was because I found it easier than having to worry about counting calories.
At the moment I am averaging 2Lb loss per week but its still early days.
Yes, you can do a water fast for 36 hours. The only reason Dr. Mosley suggests eating a small amount on a fast day is because a water fast (zero calories) is very hard for most people. He designed the diet to be sustainable. If it gets too hard, people are less likely to stick with it. There are no health risks involved in going without food for a day. You will likely get more of the health benefits. I do not agree that you will wake up and want to pig out. Like I said, the ONLY reason for taking in a small bit of calories is to make the diet easier. And YES, if you eat nothing, you will save an additional 500-600 calories per week, which you can put toward additional weight loss.
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