There is a diet called "fasting two times a week diet" or "the 5:2 diet". You eat only 25% of your normal intake two times per week, and the rest of the week you eat extra to make up for it. It claims to make you healthier, help protect against Alzheimers and cancer, and make your body get "younger".

Horizon: Eat, Fast And Live Longer is the BBC documentary about the 5:2 diet. http://vimeo.com/54089463

With five feast days and two fast days, you can have normal food for most of the week and only cut down for 48 hours.


And, best of all, you only have to calorie count for two days.

Those days aren’t total fasts but do involve eating a lot less than usual – 25% of what you’d eat to maintain your weight.


Does anyone have any substantial proof of this being true, or wrong? Are there any other studies of this?

What I am most curious about is if the "fasting" improves health.

Studies conducted by the Baltimore National Institute on Aging reveal that fasting once or twice a week lowers Insulin-like growth factor 1 ( IGF-1 ) levels; a lower IGF-1 level encourages fat burning and can protect the brain against diseases such as Alzheimer's disease and Parkinson's disease.3 Tests conducted on mice have revealed that controlling the levels of IGF-1 through fasting can promote longevity; high levels of IGF-1 in later life promote aging, although it is needed in youth for growth.2 However, the general medical consensus is that fasting has not been researched extensively enough to determine if there are benefits.


According to the wiki link, and according to the documentary it increases life length. It has been tested on rats and they live longer when they fast 2 days a week.

What I am looking for is not "I think it's bad because I have heard balanced diet is good". What I am looking for is some substantial proofs, some other research than what I have sent preferably done on humans.

There are claims of 5:2 being unsubstantial and untested.

What the NHS says:

The evidence surrounding the benefits of the 5:2 diet and intermittent fasting (IF) are limited when compared with other types of weight-loss techniques.

  • Presumably it makes sense. It's basically extremely short term crash dieting, with reversion to normal intakes in between. You will fail to lose weight with this if you overcompensate on the so-called feast days (which are actually just normal intake days)
    – bobobobo
    Commented Apr 2, 2013 at 0:31
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    @Wertilq the usual claim that losing weight makes you live longer by definition no doubt. I contest however that fasting upsets the body chemistry which can't be good, it's far better to have a balanced diet spread over all the week that has the same total intake in dietary products spread over 5 days using this diet. Also, fasting 2 days would make you very hungry and probably overeat the days after, thus ensuring you actually end up consuming MORE than before.
    – jwenting
    Commented Apr 2, 2013 at 10:49
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    Source on that?
    – Wertilq
    Commented Apr 3, 2013 at 6:08
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    At a minimum this kind of thing can focus your awareness of food...I've tried a less extreme version of this and found that I snacked less on non-fast days (in addition to eating less on "fast" days). And since snacking is my big problem, even if I ate bigger meals on feast days it was a win overall. Lost about ten pounds (out of twenty or a little more I needed to lose) in less than a month without great discomfort or much change in my daily routine. And kept it off through the stressful events of the months since then. Which is not evidence in the Skeptics.SE sense, but might be useful. Commented Sep 4, 2013 at 19:22
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    I tested it out for about 4 months. I noticed I was grumpy, got into arguments and had less patience on fasting days, and I felt more... clear in mind day after fasting. I also really wanted to eat greasy and fatty things day after.
    – Wertilq
    Commented Sep 4, 2013 at 20:18

1 Answer 1


Your question asks if there are any health benefits from intermittent fasting, preferably on humans vs mice.

There is a very old 1957 Spanish study which was re-examined by JB Johnson in 2006 [1] where subjects in a nursing home alternately consumed either 56% or 144% of their daily caloric requirement over 3 years. There was a highly significant difference in the number of days spent in the infirmary with 123 spent by the 60 study subjects and 219 days by the controls. Deaths were twice as high in the controls ( 13 vs 6 ) but this was not significant.

A much more modern study from 2011 over 6 months [2] looked at weight loss and metabolic markers on 107 young overweight human females who were either randomized to intermittent energy restriction [IER] (25% on 2 days a week) vs continuous energy restriction [CER], and found:

IER is as effective as CER with regard to weight loss, insulin sensitivity and other health biomarkers, and may be offered as an alternative equivalent to CER for weight loss and reducing disease risk.

So, this has shown that IER has health benefits with the need only to fast 2 days a week. Furthermore, fasting insulin and insulin resistance falls were greater in the IER group, though modest in both. If lipid levels are related to risk for dementia, then falls in LDL and total cholesterol were seen in both groups.

[1] Johnson JB, Laub DR, John S. The effect on health of alternate day calorie restriction: eating less and more than needed on alternate days prolongs life. Med. Hypotheses 2006 Mar 10;67(2):209-11. doi: 10.1016/j.mehy.2006.01.030. PubMed PMID: 16529878.

[2] Harvie MN, Pegington M, Mattson MP, Frystyk J, Dillon B, Evans G, Cuzick J, Jebb SA, Martin B, Cutler RG, Son TG, Maudsley S, Carlson OD, Egan JM, Flyvbjerg A, Howell A. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes (Lond) 2011 May;35(5):714-27. doi: 10.1038/ijo.2010.171. PubMed PMID: 20921964.

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    Just to clarify, my reading of it is that, for an aggregate of calories consumed over the week, they were of the same effectiveness, i.e. the same total reduction in calories resulted in the same amount of weight lost whether you spread it over 7 days or over 2. Commented Jun 2, 2014 at 16:30
  • I think so, calories consumed were the same in control and subjects averaged over the week.
    – HappySpoon
    Commented Jun 2, 2014 at 20:44
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    Thank you. I wanted the clarification because the claim is sometimes made that intermittent fasting "supercharges the metabolism", or somesuch nonsense. But in the end, it's all about the calories and what works best for people in terms of not realizing they're starving themselves. :) Commented Jun 2, 2014 at 22:09
  • @HappySpoon Interesting, but as you say in the comments, this doesn't show the positive effects of 5/2 diet itself, but rather that a lowered calorie intake is positive.
    – Wertilq
    Commented Jun 3, 2014 at 10:59
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    @Wertilq the second study quoted shows that the 5:2 diet is equivalent ( or possibly better ) than the continuous caloric restriction method in health benefits. Your question only asked for evidence of health benefits, not that it was better than any other diet.
    – HappySpoon
    Commented Jun 3, 2014 at 22:25

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