Intermittent Fasting - A Deep-Dive Review Of The Basics: Benefits And Biology
IF Insider No. 44
In our last issue (IF Insider No. 43) we helped you decide if a fasting “reboot” was right for you as a reset for the New Year. In this issue, we are going to bring you a review of the basics of intermittent fasting…this includes how fat storage and fat burning work, how fat-adaptation works, and also a look back at one of the most important journal articles that was published in the last two years on IF and what it can teach us.
For our premium subscribers, in this week’s Research Spotlight, we are taking a closer look at a Japanese study that dietary flavanols found in some common foods may actually help to lower body fat.
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Intermittent Fasting: A Deep-Dive Review of the Basics Including Benefits And Biology
Sometimes we get so caught up in just one or two of the obvious benefits of IF that we forget about the rest…so here is a brief review of the benefits:
One of these of course is weight loss, and this is why the majority of people take up the practice. They come for the weight loss and hang around for the other benefits which are considerable and include:
protection from Type 2 diabetes
possible protection from Alzheimer’s and other neurodegenerative disorders
increased autophagy (cellular cleansing)
more mental clarity
research is now showing that IF can actually slow or reverse aging to some degree.
The Biology Of Fasting And Fat Loss
Let’s also review a little bit of the biology of exactly how fasting works, as it can get a bit complicated and we tend to forget.
First let’s get back to why the majority of people take up intermittent fasting, including myself, and that is to lose weight. Specifically to lose body fat.
Well, what is fat exactly? Fat is simply energy from your food that is in storage. Our bodies have a way to take that excess food energy and instead of it going to waste, puts it into storage in the form of fat. This is a very handy thing to be able to do...so if you were unable to find food for some reason, for a time, your body can pull energy from your fat stores and survive.
The Body’s Self-Storage Trick
Let’s look a little deeper. Just how does our body accomplish this self-storage trick?
The key to this is the hormone insulin.
When you eat, your pancreas goes to work putting out insulin, and the level of insulin in your bloodstream rises. This increased insulin is the key that enables energy in the form of glucose to get into the cells to be used AND it unlocks our storage facility enabling food energy to be put away in two different forms for later use.
Carbohydrates from your food are broken down by your digestive system into separate sugar or glucose units. Protein metabolism is a different thing and is not really involved in the storage of fat so we won’t get into that here.
These sugar units get chained together in long strings called glycogen and this glycogen can get stored in two places, your liver, and muscles, where it’s fairly easy for your body to get to it and use if needed.
But there is not a lot of room in your liver and muscles for this so with any excess at all your liver starts converting it into fat. Some of this fat stays in the liver but most of it gets transported and deposited elsewhere in the body...to places most of us know all too well, like your abdomen, thighs, etc.
Compared to the liver and muscles, which have little room for excess, your body doesn’t have this limitation and as many of us have seen, can pack on pound after pound after pound of fat without seeming to ever reach a threshold. Unlike the fat in the liver and muscles, which is easy for your body to get to for fuel, the energy in the fat deposits is more tightly locked up, which all of us have observed in the past when we try to lose weight.
So to recap: when you eat, your body increases insulin and signals your body to store energy as glycogen in the liver and muscles, where it’s limited but easily tapped into, and in body fat deposits where it’s nearly unlimited but harder to get to.
We’ve seen what happens when you eat so now let’s look at what happens when you fast, which is the exact opposite process.
When you fast, your blood level of insulin falls as well as the level of glucose (blood sugar.) This signals your body to search for energy that is stored away because there is no food coming in to fuel your immediate metabolic needs.
Since the stored fuel in the form of glycogen in your liver and muscles is easily accessible, that’s where your body goes first. So the glycogen gets broken down to glucose and your cells can then use that glucose for energy. You can go about 24 to 36 hours on stored glycogen by itself before your body has to turn to your fat deposits for fuel.
It takes 5 or 6 hours before the food we eat in a meal gets broken down and absorbed by your digestive system, so you can see that someone who is eating multiple meals and snacks all day, then goes to bed, gets up, and immediately has breakfast..their bodies likely got the energy they needed after the meal was digested from stored glycogen, so no fat was ever burned.
And during the day, if you are eating multiple small meals every 3 hours, your body never even has to dip into your stored glycogen...it just uses what you take in. So you’re never burning any fat and if you are taking in more energy that can be used, you are likely adding to your fat stores.
The Two States
There are really only two states that your body can be in and it’s always one or the other:
Either you are fed and your insulin levels are high and you have the potential for storing fat or you are fasted, your insulin levels are low and you have the potential for fat burning. It’s one or the other all the time. Most people at least in the United States, are nearly always walking around in the fed state.
The Journal Article That Brought IF To Mainstream Medicine
On December 26th of 2019 a review article with the title Effects of Intermittent Fasting on Health, Aging, and Disease was published in the New England Journal of Medicine, one of the most prestigious and widely respected scientific publications in American Medicine. This article got widespread attention, made the headlines on all the major news networks but more importantly finally brought the promise of intermittent fasting to the mainstream medical community.
While this article delves pretty far into the biochemical pathways underlying IF’s effects, we are not going into these too deeply but what we would like to do is to bring out several points the authors make that we think are important for you to understand.
When you take up a practice of daily intermittent fasting, the stores of glycogen in your liver become gradually lower and lower and lower until after a period of a few weeks, when you fast, the body does not have enough glycogen in the liver to draw from so it goes to your body fat and begins to burn that. So now you have become what is called fat adapted...you have the ability to easily burn carbs when in the fed state which are coming directly from the food you eat and when you fast, your body efficiently switches to fat burning.
This is called metabolic switching...from carbs as a fuel source to fat as a fuel source. The fat is broken down into fatty acids and glycerol and the liver further breaks down the fatty acids into ketone bodies...which is a major source of energy especially for the brain during fasting.
These ketone bodies are not just used for fuel but they act as a molecular signal which regulates the activity and expression of numerous proteins and molecules which in turn has a profound effect on health as well as aging. Not only do these ketone bodies have effects on metabolism but they stimulate the expression of a gene responsible for brain-derived neurotrophic factor or BDNF, a protein that has positive implications for brain health as well as mental health disorders and neurodegenerative disorders such as dementia and Parkinsons and the like.
So some of the benefits of IF come from weight loss such as decreased blood pressure, decreased heart rate, the effectiveness of endurance training, abdominal fat loss, etc and some come from these other pathways. So with multiple pathways activated by a common activity, in this case, IF, you can see why it has such a wide range of effects.
Research shows all of our organ systems respond to the cycle of fasting and feeding with what is called an adaptive coordinated stress response which are biochemical pathways and includes such things as increased expression of antioxidant defenses, repair of DNA, quality control of proteins, the production of new mitochondria, increased autophagy and decrease in inflammation.
These responses also include enabling cells to remove proteins and mitochondria which are damaged and then take the undamaged molecules and recycle them. Research shows also that when intermittent fasting is combined with regular exercise, even more long-term health benefits are conferred which leads to resilience and disease resistance.
The New England Journal paper conclusively states, and we will paraphrase this for you here... that many of the health benefits of IF are not due to just weight loss alone but come from this complex adaptive cellular response that is integrated both within and between organs so that during fasting, your cells activate pathways that serve to improve your glucose regulation, increase your body’s resistance to stress and suppresses inflammation. Then when you eat (called the refeeding period) your cells engage in a process of growth and plasticity.
But as the authors of the paper state: Most people consume three meals a day plus snacks, so intermittent fasting never occurs. In people who do not fast or are sedentary, these pathways are not activated and these people never tap into the immense potential for healing that their bodies would naturally provide for them if they would only take advantage of it.
Fortunately, if you are a practitioner of intermittent fasting, you are not in this camp!
Why It Matters
Understanding the biological basis for the miraculous processes that go on every second in our bodies gives such an appreciation for the lives we have been given.
“Biology is the most powerful technology ever created. DNA is software, protein is hardware, cells are factories.”
~ Arvind Gupta (b. 1961) - Indian toy inventor and expert in science. His TED Talk, Turning Trash Into Toys for Learning was rated among the ten best TED talks compiled by Sir Ken Robinson. His webpage, Toys From Trash, is also delightful.
What We Are Reading 📚
With each issue, we bring you a short blurb on what we are currently reading or watching, including books, articles, podcasts, videos, movies, and research papers of value.
Denise - I recently learned that Dr. David Sinclair, author of Lifespan: Why We Age—and Why We Don't Have To, has a new podcast, appropriately called, Lifespan with Dr. David Sinclair. You can find it on all the podcast hosts, as well as on YouTube.
The second episode is the one that caught my attention: What to Eat & When to Eat for Longevity. And you may have guessed by now, that the number one recommendation Dr. Sinclair has for increasing your lifespan is to eat less frequently, i.e. time-restricted fasting a.k.a. intermittent fasting. He and his co-host discuss:
…how frequently we should eat, what food we should avoid, and what food we should pursue. They discuss the science behind how a "low energy state," which can be induced by a period of fasting, combats aging and promotes health. They also walk through research that points to the benefits of a mostly plant-based diet for slowing aging and offer key insights into when to eat and what to eat to maximize longevity.
Ellen - For most people who practice intermittent fasting, coffee is a vital part of our program, as it acts as an appetite suppressant, has a variety of health effects and it also simply just tastes good!
I love cold brew coffee and purchase the concentrate (Chameleon brand) at the grocery store. But in the back of my mind, I’m always thinking maybe I should really learn to brew it myself.
So when I came across Jessica Easto’s book Craft Coffee: A Manual - Brewing A Better Cup At Home, my senses perked up (pun intended!) Her book was named a top food & drink book of 2017 by Food Network, Wired, Sprudge, and Booklist.
Unlike many other coffee books, this one focuses solely on coffee, not espresso, and teaches you to master ten manual methods from the pour-over to cold brew.
Did you like this article and learn something new? If so, please let us know in the comments! Questions and suggestions for future articles are welcome, too!
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