Scientific Studies Supporting 16/8 IF?

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Scientific Studies Supporting 16/8 IF?

This topic contains 8 replies, has 6 voices, and was last updated by  dykask 5 years, 9 months ago.

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  • Hi all,

    Just came across this forum, hopefully can help answer my question.

    I am a healthy weight so particularly interested in the health benefits of IF. In particular encouraging Ketosis (burning fat for fuel) and autophagy (the process of your body “cleaning up” damaged and old cells). I ended up following a 16/8 fast as it suited my lifestyle but looking at the science all the studies I can see in humans are on minimum 24 hour fast, and Dr Longo who is a leading scientist in the field uses 5 day fasts every few months i believe in his data.

    There are some mouse studies on 16 hour fasts (which would mean a longer period of fasting for humans to be applicable because mice’s metabolism, bodyweight so much smaller, 16 hour fasts is more like 5 days for humans) so i wonder if the idea of 16 hour fasts in humans leading to benefits is a bit of confusion from using mouse studies and its the longer fasts that yield benefits.

    Can anyone cite any studies of the 16/8 being beneficial in humans?

    Many thanks

    Hi Tom:

    Here is the only study I have found on the subject. It studied healthy but not overweight people. The meal pattern was 23:1 – one meal a day:

    Hi Tom,

    Im in maintenance mode, have been for over a year now. I water fast once per week every Monday. So last meal is on Sunday night at 6pm and next meal is Tuesday morning. About a 36 hour fast. I measure my blood glucose and ketones. Ive only done measurements after 24 hours. At the 24 hour mark I am in ketosis. How much earlier I enter ketosis I cant say. I suppose I should measure every two hours or so to find out when exactly I enter ketosis. After 16 hours? Maybe? I suppose if you eat a ketogenic diet then yeah it would be easy. Not a big fan of being on a pure keto diet though.

    Don’t expect to reap any benefits for several months. That is the one thing I have noticed as a consistent theme on the forum. “I tried it for one week and it didn’t work.” It takes a lot longer than a week to elicit a change. If you go down a particular diet regimen you wont reap any rewards for about 6 months. Granted that is based on a study of n = 1 (i.e. me). I noticed a distinct change after 6 months. I get my bloods taken every six months. I change one particular aspect of what I eat, wait six months and then get bloods taken to see if it has had a positive or negative effect.


    Thanks for the replies. Hmm seems there isn’t too much science backing up the shorter periodic eating and the real health benefits are more once you get into the 24+ hour fasting.

    For those of you only interested in fatloss and body composition there is a good source of info at He seems to be the guy that introduced the 16/8 concpt. But is very much focused on fatloss and muscle preservation/growth rather than longevity etc

    Hi Tom,

    I am a 5:2er of nearly 2 1/2yrs, ending my weight loss phase 4 months ago. I’m on 5:2 fir health and weight normalisation reasons. My latest blood readings are almost perfect, still in normal range. I’m mid 60’s female with a serious chronic health condition with both aerobic and non-aerobic exercise contraindicated. I’ve not done ketone tests.

    Because of my lack of exercise my calorie needs above BMR are only 250cals/day. For my personal circumstances, about 1 yr into 5:2 I opted to do 16:8 on my 5 non fast days per week. On my 2 FDs I start my ‘fast’ on Sunday night and no cals eaten or drunk till after 6pm on Monday night. So basically I’m 16:8 5days and 21:3 for 2 days, Monday and Thursday. My general health has improved greatly, my medicos are saying ‘brilliant’, And my General Practitioner says she rarely sees a blood profile ad good as mine and sees a bone mineral density result as good only once every few years. I also believe my chronic , incurable condition is beginning to improve in tiny bits in response to the long period of time of consistent 5:2 fasts, in ways that have not been seen before. I have Myalgic Encephalomyelitis, commonly known as Chronic Fatigue Syndrome. On FDs I do 1/4 of my TDEE which is 360 calories.

    I don’t believe Lean Gains would have done this on its own. To me, the 2 Fasting days have been the crucial element in my journey of improving my health.


    @tomhgriff1 – Ketosis will really depend more on what you eat as 16 hours of fasting isn’t really that much. For most people it can take a day or more of fasting to deplete stored glycogen and it also takes time for the body to ramp up lipolysis. 16 hours of fasting helps but if one can easily eat enough in eight hours to replace any depleted glycogen. So if you are really interested in ketosis you need to eat a ketogenic diet.

    Autophagy probably is always happening to a small degree. The studies I seen though indicate that it takes days of no calorie intake for large increases in autophagy. It will be ramping up but probably the difference would be slight in just 16 hours of fasting. I don’t have any reference handy. I think even the 4 day fasts that Dr. Longo uses are on the short side for autophagy. I’m still learning about this myself and my longest fast has been just 84 hours.

    Basically if you are using a 16:8 IF pattern, for many people it helps with fat loss and possibly improving insulin sensitivity and may even help increase Human Growth Hormone but one shouldn’t expect too much from it. After all if you go back 50 years to when I was a kid, it was common to eat in a 14:10 pattern without much snacking. Overall there was less obesity and metabolic problems but no one even would have considered 16 hours without eating a fast, it was almost normal.

    The reason I got interested in 5:2 is because the fasts twice a week are around 36 hours if you don’t eat. At that level the fasting process getting underway and while it is still too short for profound changes, at least most of the bodies glycogen is depleted. However most people here eat a 500+ calorie meal during the fast breaking it into two shorter fasts. I think that is okay because most are just trying to burn fat. Burning fat is probably the main benefit of the shorter fasts because it gives the body enough time to start burning fat.

    Take a look at this blog:

    Dr. Fung has many posts where he talks about various studies and the impacts. While he is mostly focused on reversing type II diabetes, he really does cover the bases and shares much data from various studies.

    I also recommend Brad Pilon’s “Eat Stop Eat” as he also has gone through a great deal of research. However it isn’t free and you have to get the PDF from him, probably end up costing around $15 after taxes, etc.

    His blog is sometimes interesting too:

    Finally Dr. Peter Attia isn’t so much into fasting but has done a lot of experimentation with ketosis is a great resource.

    Thank you for the further responses.

    Heres another question if you have the time.

    One of the benefits of IF is the fact is decreases the growth hormone IGF-1 (insulin-like growth factor) which is highly correlated to cancer. In fact in both animal and human studies where IGF-1 receptors are missing or damaged the host can’t develop cancer.

    Dr Longo one of the most eminent scientists on IF has proven fasting can decrease IGF-1 by 50%…. great news.

    HOWEVER, there are a lot of health benefits of having increased growth hormone levels. It is anti aging, boosts muscle development, keeps skin and hair young etc etc and a lot of IF fasting studies prove fasting can increase human growth hormone by several thousand percent!

    Isnt this a contradiction seeing as IGF-1 is also a growth hormone?

    The way i see it is either one of these studies is wrong. They contradict each other and cancel the benefits out, or its the holy grail of getting human growth hormone like benefits without raising IGF-1?

    Any of the biologists among you know the answer?


    If you’re still looking for some research here you go:

    I’m also doing 16/8 but only started a few days ago so can’t comment on progress

    @kemron I was really surprised by impact on 16/8 on IGF-1 and other hormones. I wonder if the people in the study were actually moved to a much lower protein diet than they were used too. In any case it indicates there is plenty of value in the 16/8 pattern.

    @tomhgriff1 – My weak understanding of IGF-1 vs HGH. IGF-1 helps build muscle but is also closely associated with aging and cancer cells are sensitive to it. HGH seems better for muscle development which helps with metabolism, but it also stimulates the production of IGF-1. HGH is very sensitive to Insulin and even small amounts of eating and greatly impede its production. So typically as we start to build up HGH, it is putting the breaks on its own production. HGH often occurs with Glucagon and both of these hormones stimulate fat burning. HGH is strange in that is promotes muscle development while promoting the breakdown of fat. My take on IGF-1 is that insulin is like the master mind fat builder and IGF-1 is the enforcer. However I’m just trying to learn this stuff myself. Often people trying to build muscle anyway the can inject both HGH and IGF-1. The problem is there are balances of these hormones and injections tend to throw things out of balance. With fasting we get natural production of HGH and Glucagon in a balanced fashion that doesn’t seem to have many of the side effects of injecting the hormones. People living past 100 also have low levels of IGF-1. So it is difficult to have this balance of high HGH & Glucagon with low levels of Insulin & IGF-1. We need all the hormones it is more about the balance of them. For most of us the goal it to have less fat and live longer.

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