What does science say about intermittent fasting? | Gin Stephens and Professor Tim Spector

It seems like every day, someone new mentions intermittent fasting. But what is it, exactly?

There are myriad options — from the 5:2 diet, with two days of extreme calorie restriction each week, to the warrior diet, which involves eating only raw fruit during the day and a mammoth feast at night.

Whatever the approach, intermittent fasting involves restricting the window of time when you eat.

Supporters evangelise the benefits, promising weight loss, disease prevention, and even life extension.

Currently, the scientific evidence is unclear, but it's an exciting area that may be full of potential.

In today’s episode, Jonathan speaks with Gin Stephens, who has had a powerful experience of intermittent fasting transforming her health and weight. He also talks to Tim Spector, who will share what science can tell us about intermittent fasting today — and, interestingly, how much it can’t, yet. Plus, an exciting announcement about how this is set to change.

Gin Stephens is a New York Times bestselling author and podcast host.
Tim Spector is a co-founder of ZOE and one of the world's top 100 most-cited scientists.

Timecodes:
00:00 - Intro
00:10 - Topic introduction
02:28 - Quickfire questions
04:28 - ZOE’s intermittent fasting study
09:00 - What is intermittent fasting and how it impacted Gin’s life
12:16 - Demystifying intermittent fasting
14:55 - The science of intermittent fasting
25:08 - Starting intermittent fasting
27:16 - What am I allowed to have during intermittent fasting?
32:07 - The first 28 days of “clean” intermittent fasting
34:54 - Intermittent fasting and the microbiome
39:19 - Correlation with circadian rhythms
41:28 - How important is consistency when time-restricted eating?
43:47 - On intermittent fasting & women’s health
46:07 - Summary
47:20 - Goodbyes
47:40 - Outro

Books:

[biggyziggy]

I am a 54 year old menopausal woman … last year l had not so good blood test results and l knew it was up to me to make a change ! … l started Intermittent Fasting and l worked up to 20/4 over 20 weeks. I was interested in what my bloods would be … so l had another blood test. My Doctor rang and asked me to come in and see her … so l did and she was WTF are you doing !!! … my bloods were PERFECT 🤩 ( obviously other than hormones because l am peri menopausal ) l have lost 12 kgs ! … my appointment was for 10 min we actually sat for 1/2 hour and she was taking notes … l told her about Gin and Dr Jason Fung … she was pretty amazed 😊😊 … edited 21 st March 2023 .. l have now lost 20 kgs 🥳

[RicktheRecorder]

I've been on a 6 hour window (13h30 -19h30) for about 3 years now. Much more energy, never hungry. Also restricted calorie intake, lots of vegetables and fermented foods. 72 years of age.

[ShaunPeterKelly]

I've been fasting for year's and found it easy, when feeling hungry during my fast I drank some warm water and the hunger disappeared.
I'm in my 80s, feeling great and people say I look 20 years younger.

[Dahabmermaid]

I started IF at the start of Covid to lose my menopausal weight and it worked within a few months and it transformed my relationship with food and never need to snack any more and my body is still happy with my 8 hour eating window and now it’s a lifestyle thing and surprisingly very freeing.

[iannixey]

I’m a 47 year old truck driver who sleeps in their cab 5 nights per week, after using intermittent fasting( sometimes using prolonged fasting) I have lost around 3 stones in about 4 months. I do try to go for a walk when I can and I am a vegan, which complicates things slightly. I do seem to feel better for doing it.

[SeeLisaSmile]

I began clean fasting in March of this year. I am 61 years old, 5'6" tall and began at 222 lbs. I did OMD (One Meal a Day), so 20/4 schedule. After 8 months I have broken 2 of my goal weights. My first was 172 lbs, and the second 166 lbs...not sure where I will stop but very happy with my weight now. I will continue with this for the rest of my life. My blood sugar is normal now, skin tags have disappeared, lines on my face have softened, I have some loose skin but I can see it firming up, and the pain in my knee has lessened. This is not a diet, this is a healthy forever lifestyle. If you haven't tried it, please do, you won't regret it!

[jemima]

I would like to add the fact that since I started IF about six months ago I have been enjoying my food so much more. I eat two meals per day ( no snacking apart from hot drinks) so when I do eat, the flavours seem to be more intense and delicious. It’s also fair to say I don’t spend so long preparing meals because there’s only two of them rather than three, therefore I get more pleasure from preparing the meals that I do eat.

[patriciaharding]

I started IF almost 4 months ago. The first 2 days were difficult, but being super motivated got me through it A-OK. From that point on it was pretty easy. After one month I was loving it for so many reasons: I didn't have any "eating guilt" or mental battles about snacking or not. It's remarkable about how much mental space that took up! No willpower or self discipline needed anymore - that was rather shocking for me. Also, bought less groceries, spent a lot LESS time in meal prep and kitchen cleanup - bonus! I decided to change to a non-inflammatory diet before I started IF because the pain of my rheumatoid arthritis was totally ruining my life.
That meant cutting out wheat and other grains, sugar, highly processed foods and dairy. I'm such a foodie, so I felt that if I had to be that restricted I might as well try IF as well since I heard that it helped to really drive the numbers down on A1C scores, which showed pre-diabetes a year ago (which totally freaked me out!) Well, here are my results after 4 months:
I've lost 33 lbs which is marvelous, my A1C is completely out of pre-diabetes range (whew!) and I no longer experience ANY pain with my RA!!
I should note here that prior to my new way of eating, I spent every day in a ridiculous amount of pain, (never less than a 5) and needed narcotic drugs to get me through my RA "flares" when my pain level was 8 or 9.
I truly have been given my life back. No more drugs. No more pain and stiffness that I'd experienced for 20 years previously! Seems like nothing
short of a miracle for me!

[LarryFournillier]

I've been living a Keto and Intermittent fasting lifestyle for the past 4 years and it's the best I've ever felt in my life. I'm 64, 5'6" and 158 lbs - IF and Keto definitely works!

[tictoc]

Worked for me
From obese to normal weight in 6 months

[francesoconnell]

When I was diagnosed as a Type 2 diabetic in 2014 aged 60 years. followed Dr Michael Mosley's 5.2 diet, I weighed 84 kg and when I reduced my weight to 47 kg. I felt amazing, not only did I have fair more energy, but was wearing the clothes size that I had worn when I was in my 20s. I did more research and I discovered intermittent fasting, I maintained my weight loss and keep it off. More importantly my HBL1C levels in my blood sugar levels have markedly improved. As take medication twice a day I decided to have a 6 hour window of eating, so I eat between 12 noon and 6 pm. I feel fantastic and will eat like this for the rest of my life. I'm now 68, apart from diabetes, I have no health issues, no aches and pains, I feel as wonderful as I did forty years.

[kathrynsloan]

I am a post menopausal woman and I intermittant fast. I feel amazing. So much better than when i am constantly eating. I feel for mentally alert, have more energy and I weight is normal and a perfect BMI.

[kevinlindsay]

I have been doing IF for about 6 months and have found now i can live quite easily on one large low carb Keto style meal a day at 5.00 pm. Lost loads of weight and feel great

[anthonyhulse]

Just coming to the end of a 48 hour fast. Feeling great: clear headed, rested, not hungry. My blood sugar is 4.8 and I’m in ketosis. 👍🏻 keto and IF are saving my life.

[TorBoy]

I've been intermittent fasting, time restricted eating, 18-6 hour eating window for about 4 years now, and usually end my fast with 1 hour of strength training, followed by a high protein meal. It is really not about the weight loss, but the other benefits such as metal clarity and a better overall feeling of good health. I've long stopped feeling hungry. There have been days where I have forgotten to eat and have done 20-22 hrs of fasting, and really, it is not a big deal. Fasting does allow me to have better weight control, as if I want to drop a couple of pounds I simply narrow my eating window a bit for a couple of days. I, too, like dark chocolate, but only in my eating window. Really, there is nothing I cannot eat, but there is a defined time for proper eating.

"Come for the weight loss, stick around for the health benefits.."

[norabalogh]

I’m 63 and have been using IF since age 55 to maintain a really good weight for me (i.e. a BMI of 22.5 for a fit, muscular woman). I do two meals a day — lunch and supper — since that fits best into my life (OMAD is too extreme for my taste and I don’t like eating that much at once, and I find eating in “meals” vs eating within a window to be simpler to manage and control and more flexible). Also I am a flexitarian — I eat everything (though no fast food or highly processed foods) and I lean in a vegetarian/vegan direction quite often. I hate low-carb eating and I also think it’s far less healthy than the way I eat..All of which underlines the fact that IF can happily and successfully be combined with various ways of eating! Also I think that doing something that “works” for you in your life is far more important than fitting in with someone else’s theories!!!

[andrewlittlecott]

I started LCHF diet in June to reverse diabetes. After one month I stopped eating breakfast (so 2 meals a day). After another month I have gone to one meal a day, no problem with hunger and play lots of sports and don't feel low on energy. Eat whatever I want for two hours (except carbohydrates). Most difficult thing was to eat fat, everything high fat and I have lost 44lbs in three and a half months. Feeling great.

[andreakumar]

Love the 16/8 window with skipped breakfast and half of the fasted hours taken care of during sleep. Really doable and sustainable.

[joycemarine]

I have been using IF method of eating for at least 2-3 years. For some of us, guidelines are necessary. Some of us are moderators and some of us are abstainers. Removing seed oils and ultra processed foods along with IF has been life changing!!!

[Glen.Danielsen]

Gin Stephen’s and Tim Spector’s words are monstrously helpful! At present, I eat two quality meals a day — at around 9:00 am and at 1:00 pm. Then I fast the remaining 20 hours. It works marvelously so far. Loved Gin’s hurricane ambiance sounds! 😊🙏🏽