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The Beginner's Guide to Intermittent Fasting, by James Clear

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I'm reading James Clear's explanation of intermittent fasting.

Intermittent fasting is not a diet, it’s a pattern of eating. It’s a way of scheduling your meals so that you get the most out of them. Intermittent fasting doesn’t change what you eat, it changes when you eat.

How Does Intermittent Fasting Work?

To understand how intermittent fasting leads to fat loss we first need to understand the difference between the fed state and the fasted state.

Your body is in the fed state when it is digesting and absorbing food. Typically, the fed state starts when you begin eating and lasts for three to five hours as your body digests and absorbs the food you just ate. When you are in the fed state, it’s very hard for your body to burn fat because your insulin levels are high.

After that timespan, your body goes into what is known as the post–absorptive state, which is just a fancy way of saying that your body isn’t processing a meal. The post–absorptive state lasts until 8 to 12 hours after your last meal, which is when you enter the fasted state. It is much easier for you body to burn fat in the fasted state because your insulin levels are low.

When you’re in the fasted state your body can burn fat that has been inaccessible during the fed state.

Because we don’t enter the fasted state until 12 hours after our last meal, it’s rare that our bodies are in this fat burning state. This is one of the reasons why many people who start intermittent fasting will lose fat without changing what they eat, how much they eat, or how often they exercise. Fasting puts your body in a fat burning state that you rarely make it to during a normal eating schedule.


Way back in 1945 it was discovered that intermittent fasting extended life in mice. (Here’s the study.) More recently, this study found that alternate day intermittent fasting led to longer lifespans.

It is a simplistic approach and I guess if you are going to try to balance simple vs in depth time consuming and mentally draining dieting for fat loss this is on the Keep it simple, stupid side. insulin levels are based on the amount and type of carbohydrates you consume. the point about burning fat vs insulin levels is true but simplistic.

Nathaniel, what would be an improvement over this?

tl;dr Fasting heals the brain.

Thank you for the links

You are very welcome, Nathaniel.

Fasting is good, I do it as well but I do eat around ten then fast until I work out, and following the workout I eat simple carbs for the insulin spike. Then I eat my late lunch and have salad and meat or other protein for dinner

Cycling carbohydrate consumption to every other day may help as well, buy I haven't researched or tried it on myself yet.

So your fast between 10 and work out is only a few hours?

James Clear thinks you need at least 12 hours of fast to get into burning mode. 

Between 9p.m. and 10a.m. Also a three hour window between carbs or one to one and a half after protein and you are good to burn fat at the gym, skill it would be better to just do completely fasted HIIT.

I'm not sure of the science of the 3 hour carb window and the 1.5 hour protein window.

If I go to the gym first thing in the morning should I eat before I go or stay in the fasting state?

Yes, and the science behind it is taught in a physiology class, I took bio, anatomy/physiology in college because I care about this kind of stuff. That class supports my understanding of the phenomena we experience at the gym. this also helps me with questions like you asked. as you say below, most definitely you don't want to eat before going to the gym 1st thing in the morning. the science behind the carb window is your body's insulin trigger mechanism, how insulin affects fat storage (positive storage and conversion of carbs to fat) vs a catabolic state (negative storage, using fat as the final energy source for muscle ATP cycle as opposed to creatine)"

Using glycogen (and no oxygen)Fortunately, muscles also have large stores of a carbohydrate, calledglycogen, which can be used to make ATP from glucose. But this takes about 12 chemical reactions so it supplies energy more slowly than fromcreatine phosphate. It’s still pretty rapid, though, and will produce enough energy to last about 90 seconds. Oxygen is not needed – this is great, because it takes the heart and lungs some time to get increased oxygen supply to the muscles. A by-product of making ATP without using oxygen islactic acid. You know when your muscles are building up lactic acid because it causes tiredness and soreness – the stitch." the above is why we don't want carbs readily available to the body for conversion during a workout."

Using aerobic respiration (using oxygen again)Within two minutes of exercise, the body starts to supply working muscles with oxygen. When oxygen is present, aerobic respiration  can take place to break down the glucose for ATP. This glucose can come from several places:

A selection of foods supplying carbohydrates, fats and oils, proteins, vitamins and minerals.

Image: Selection of foods

  • remaining glucose supply in the muscle cells
  • glucose from food in the intestine
  • glycogen in the liver
  • fat reserves in the muscles
  • in extreme cases (like starvation), the body’sprotein.

Aerobic respiration takes even more chemical reactions to produce ATP than either of the above two systems. It is the slowest of all three systems – but it can supply ATP for several hours or longer, as long as the supply of fuel lasts." 

see "uses fat reserves in the muscles" bullet point here, this is aerobic and not anaerobic using carbs. you don't really need 12 hours, that is optimal (digestion past small intestine where everything is really digested) but 3 hours is good enough to be past any insulin spike your body gets, you know that groggy feeling after eating tons of white rice or a basket of fried diced potatoes from outback steakhouse. 

like I said it isn't that simple and I don't like to get into the weeds of the details because I have argued with even certified physical trainers about this before and I know I am right because I make sure to be. it is and has been a major part of my life for 15 years. for you, I will explain because you're a great person and i have nothing but respect for you. I could go into more detail but it looks like you have done some research as well and if you have more questions feel free to field them with me.

Thanks, this helps: Go to the gym fasted whenever possible. 

if, and only if your goal is to get shredded">via GIPHY

Lol, not the shredding I had in mind. :)

Simpsons shredder couch gag gif imgur

Okay so it's better to go to the gym first thing in the morning in a fasting state. 

Most people equate “cardio on an empty stomach” with “fasted cardio.”

They’re wrong.

Your stomach is empty when you do fasted cardio but not all cardio on an empty stomach qualifies as fasted cardio.

Quick…say it three times out loud!

Let’s break that statement down so it makes some sense.

First, the proper definition of fasted cardio:

Fasted cardio is cardio done in a fasted state.

Simple enough. So what’s a fasted state?

Well, to understand that, we have to review what happens in your body when you eat food.

When you eat a meal, your body digests and breaks the food down into various molecules like amino acidsglucose, and fatty acids.

The small intestine absorbs these nutrients into the blood, where they’re met by the hormone insulin.

Insulin’s job is to shuttle these nutrients into your cells for use.

How long this takes–and how long insulin levels remain elevated–depends on the composition and size of the meal.

  • When your body is processing the food you’ve eaten, you’re in a “fed” or “postprandial” state (prandial means “having to do with a meal.”)
  • Once your body has completed the job, it enters a “fasted” or “postabsorptive” state.

When you’re in a fed state, insulin levels are higher than normal.

When you’re in a fasted state, insulin levels are at a low, baseline level.

As you can see, your body moves in and out of these states every day.

And as you’ve probably already concluded, this goes beyond how “empty” your stomach feels.

and remember HIIT>cardio 

Right, working my way up to that. :)

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