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  • The craze of intermittent fasting has gripped the world of fitness and nutritionbut

  • is this a temporary fad that will pass, or the paradigm shifting dietary intervention

  • we're led to believe? Let's find out.

  • Dr. Jubbal, MedSchoolInsiders.com.

  • Welcome to the next episode in our Research Explained series, where we do a deep dive

  • into a specific topic, spend hours scouring through the primary literature, and summarize

  • the key findings so that you don't have to. This is episode 8 — you can find the

  • full list on our Research Explained playlist. Link in the description.

  • Nutrition is a touchy subject, on the same level of politics or religion. Just look at

  • the comments on my video where I spoke about stopping a plant based diet after 5 years.

  • I'm interested in talking about nutrition from a purely health focused perspectiveif

  • your dietary decisions are based on religion or ethics, I respect that, but we'll be

  • approaching the science with a focus on health optimization. One of my favorite sources for

  • nutritional, health, and longevity based information is Dr. Peter Attia.

  • When discussing nutritional interventions with his patients, he describes three factors

  • to his nutritional framework: dietary restriction, caloric restriction, and time restriction.

  • Each factor can be manipulated independently of others to optimize for the desired outcomes.

  • Dietary restriction means limiting what you do or don't eat. For example, maybe you

  • avoid red meat or dairy. Caloric restriction means limiting how much you eat, which is

  • the most common description ofdietingthat we think of when it comes to losing weight.

  • Time restriction limits when you do and don't eat, which brings us to intermittent fasting.

  • Speaking about intermittent fasting and similar interventions is confusing because most people,

  • and often even researchers, aren't careful about what they're exactly talking about.

  • Fasting is refraining from eating. When we refer to fasting, we normally are referring

  • to water-only fasts, where consuming water is ok, or even teas and minerals, but not

  • foods or drinks with any calories, sweeteners, or the like.

  • When you hear the termIntermittent Fastingbeing used by the public, they're usually

  • referring to time restricted feeding (TRF) instead. Time restricted feeding is where

  • you limit the hours during which you eat each day to a feeding window. Most people without

  • any effort normally stick to roughly a 14/10 window, meaning they'll eat for 14 hours,

  • and fast for 10 hours while they sleep and a little bit before and after. The window

  • can be expanded to anything you want. When starting out, you may do 12/12, but eventually

  • transition to the popular 16/8 or even 18/6.

  • Alternate day fasting (ADF) is somewhat of a misnomer, since you don't normally go

  • a full day without eating anything. Rather, every other day you switch to doing something

  • other than eating ad libitum, meaning without restriction. Usually, these days are hypocaloric

  • with 1,000 or 500 calories allowed.

  • Intermittent fasting (IF) in its most strict form is undergoing a fast of at least 24 hours

  • at some frequency, or intermittently. For example, that could mean doing a 72 hour fast

  • once every quarter, or a 5 day fast once per year. A true prolonged fast like this would

  • only include water, tea, and minerals with zero calories.

  • As time restricted feeding is what most people are referring to when they speak about intermittent

  • fasting, that's what we'll be covering here.

  • Weight loss boils down to a simple measurement of calories in and calories out. If you're

  • eating more calories than are burned, you'll gain weight, and if you're taking in fewer

  • calories than you burn, you'll lose weight. For this reason, dietary interventions for

  • weight loss are primarily focused on continuous energy restriction (CER), or in other words,

  • eating as you would normally, but just eating fewer calories. The issue with CER is that

  • adherence is poor, typically declining within 1-4 months.

  • A recent review by Rynders and colleagues from 2019 concluded that, based on current

  • literature, “intermittent fasting does not seem to produce greater weight loss than continuous

  • energy restriction.” please do a highlight effect on the relevant line on page 18 of

  • the PDF, like how Jeff Nippard does so in his videos that reference scientific papers

  • However, “adherence to weight loss interventions is the greatest predictor of weight loss success

  • bottom of page 14, and some patients may respond better to caloric restriction, while others

  • will respond more favorably to intermittent fasting or time restricted feeding. Few studies

  • were carried out long enough to properly assess adherence of the two different protocols.

  • Interestingly, time restricted feeding seems better at preserving lean mass per a 2016

  • study by Moro and colleagues compared to continuous caloric restriction. Count that as a win for

  • time restricted feeding.

  • While IF is moderately successful for weight loss, there are a variety of interesting metabolic

  • effects that occur. Kahleova et al compared time restricted feeding to caloric restriction,

  • and found greater improvements in fasting glucose, increased oral glucose insulin sensitivity,

  • decreased C-peptide levels, and decreased glucagon levels in the TRF group.

  • Sutton and colleagues in 2018 found that men with prediabetes who performed time restricted

  • feeding experienced improvements in multiple cardio metabolic health markers, beyond what

  • would occur from simple weight loss.

  • But what if you're healthy without any chronic medical conditions? A meta-analysis and systematic

  • review by Cho et al. in 2019 concluded thatintermittent fasting improves glycemic

  • control and insulin resistance with a reduction in BMI, a decrease in leptin level, and an

  • increase in adiponectin concentration,” which are generally considered favorable changes

  • for most individuals. top of page 9 Cabo in 2020 also highlighted the benefits in blood

  • pressure, heart rate, endurance training effects, and abdominal fat loss.

  • Cognitive effects have been primarily studied with regards to caloric restriction, not time

  • restricted feeding, although it's not unreasonable to assume similar findings. After all, time

  • restricted feeding and other intermittent fasting protocols often lead to decreased

  • caloric intake compared to feeding ad libitum.

  • Studies in animals show enhances in multiple domains of cognition, including spatial memory,

  • associative memory, and working memory. Caloric restriction has been associated with improved

  • verbal memory in older adults, and in a separate study involving overweight adults with mild

  • cognitive impairment, 12 months of caloric restriction led to improvements in verbal

  • memory, executive function, and global cognition. More recently, Leclerc et al in 2020 performed

  • a large multi center randomized trial demonstrating that 2 years of daily caloric restriction

  • led to significant improvements in working memory.

  • Stress isn't always a bad thing. With intermittent fasting and time restricted feeding, cells

  • are forced to cope with the lack of a relatively continuous glucose source and engage in a

  • coordinated adaptive stress response that lead to increased expression of antioxidant

  • defenses, DNA repair, protein quality control, mitochondrial biogenesis, autophagy, and down-regulation

  • of inflammation.” bottom left page 2544 from Cabo 2020

  • The effects on aging are likely present but not yet well established. While several studies

  • have demonstrated benefits to the aging process in animals, the evidence is less clear cut

  • when it comes to human longevity and healthy lifespan. After all, we haven't been able

  • to research IF or TRF for decades among clinical subjects.

  • In terms of cardiovascular disease, intermittent fasting has been associated with improvements

  • in multiple cardiovascular markers, including blood pressure, resting heart rate, HDL and

  • LDL cholesterol, triglycerides, and insulin resistance. Additionally, IF has been associated

  • with reductions in markers of systemic inflammation and oxidative stress that are associated with

  • atherosclerosis, which is the clogging of your arteries.

  • Next, does the time of day during which your feeding window is scheduled matter? Jamshed

  • and colleagues in 2019 studied early time restricted feeding (eTRF) by shifting the

  • entire feeding window earlier in the day. While far from a perfect study, it demonstrated

  • several interesting findings: first, early time restricted feeding resulted in lower

  • average glucose and insulin levels. Second, avoiding food for a prolonged period before

  • bed was also associated with lower nighttime cortisol and overnight glucose. And third,

  • there was increased expression of LC3A, an autophagy gene, suggesting that more autophagy

  • occurred with early time restricted feeding.

  • Evidence-based medicine focuses on making treatment decisions based on the best evidence

  • available in the scientific literature. It's fantastic at addressing things like infectious

  • diseases, because infections are acute and binary in outcome and interventions are generally

  • straightforward, like an antibiotic or antiviral, thus making measuring inputs and outputs relatively

  • straightforward.

  • The problem, however, is that most things related to health are much more complicated.

  • Those opposed to intermittent fasting are quick to saythere isn't sufficient evidence

  • to support a fasting protocol for disease X or Y, therefore you should not do it.”

  • But to most accurately assess the situation, you need to compare the risk of the intervention,

  • which is what we normally think of, with the risk of not doing the intervention, which

  • people are less likely to consider.

  • I am not saying that you should begin time restricted feeding or intermittent fasting,

  • particularly if you have another pre-existing medical condition, and you should speak with

  • your physician. I am saying, however, that if there is a favorable asymmetric risk profile

  • for you personally, meaning the potential upside is relatively large and the potential

  • downside is relatively small for any lifestyle intervention, experimentation may not be a

  • bad idea.

  • After consulting the literature and considering the potential upsides and downsides in my

  • own personal life, I decided to give it a shot. I first started in 2017 when I was in

  • plastic surgery residency, but I quickly realized that I was losing too much weight since I

  • couldn't eat while in the operating room. I then started again about a year ago, back

  • in 2019.

  • I've been doing time restricted feeding for close to a year now, and I'm enjoying

  • it enough to stick with it. It's also been a gateway intervention of sorts, paving the

  • way for me to perform 36 and 48 hour fasts a few times, and has even been a practice

  • in building discipline. I just released a video on my personal channel going over my

  • experience, including the benefits and drawbacks I've experienced over the last year. Link

  • in the description.

  • Thank you all so much for watching. If you've tried intermittent fasting or time restricted

  • feeding, what was your experience like? Let us know with a comment down below. Much love,

  • and I will see you guys in that next one.

The craze of intermittent fasting has gripped the world of fitness and nutritionbut

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間欠的な断食 - 事実か虚構か?科学が実際に語っていること (Intermittent Fasting - Fact or Fiction? What the Science Actually Says)

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    Summer に公開 2021 年 01 月 14 日
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