Shortcut to Slim

Season 1: Episode 6

Intermittent Fasting: The Science of Cellular Metabolism

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I know I promised I would finally get to sugar cravings and gut bugs, but after the last episode a lot of emails came in asking about the science behind IF, so here we are in (another) unexpected part 2…

(If you've hit a plateau with weight-loss or you still think breakfast is the most important meal of the day… read on)

So what is intermittent fasting?

Fasting intermittently--voluntarily going set periods without food on a specific schedule.

Most IF'ers eat for 8 hours a day, fasting the other 16. This is called the Leangains method. It doesn't matter when you start your window, just as long as it's the same window each day.

I first blogged about IF back in October 2012 when a bodybuilder suggested it to me. (I'd plateaued for the second or third time.) I ignored him, rattling off conventional wisdom about how breakfast was the most important meal of the day, you have to eat within an hour of waking up, you need 6 small meals, not eating was bad, blah blah blah

(NONE of that is true, btw. See STS episode 5.)

Noel didn't offer a scientific rebuttal, just a simple “well, I do it and look at me.”

And sure he was gorgeous.

Ripped, 6-pack that looks airbrushed. Lean! Gorgeous skin too.

But since I liked science, and excuses, I figured well, he's a dude, and he probably has a superpower metabolism or special DNA that I don't… so that explains it.

Then The 8-Hour Diet was published in 2013. As much as I wanted to poke holes in another “fad” diet book -- when I read the actual science, I couldn't. Not completely anyway.

Remember when I was talking about the “slow metabolism” myth last week and I said the question shouldn't be: “what can I do to speed up my metabolism” but instead:

“what can I do to make my body burn more fat?”

This is where intermittent fasting comes in. It's not a perfect cheat. You still can't eat all you want, all calories still count and all that...I'm getting ahead of myself.

How does fasting work for promoting fat burning?

In two ways.

First, it powers up your mitochondria--the “battery packs” in your cells that form the basis of your metabolism, and second, intermittent fasting promotes fat burning.

The Science of Cellular Metabolism

Most of the cells in your body are a caboodle of organelles, mini organs called mitochondria. This is where the biochemical processes of respiration and energy production occur.

Zinczenko, the former Editor-in-Chief of Men's Health (magazine), and author of the 8-Hour Diet, compares mitochondria to dimmer switches, garden hoses, and home generators, because they increase and decrease energy flow, and act as our own personal power plants.

Basically, these guys are the engine in my Prius vs. Hummer metaphor.

And Like all engines, mitochondria will burn fuel more efficiently, produce more energy, and throw off less waste, if they are properly maintained and not overused.

Except when you eat all day, your mitochondria never get a break from processing calories.

It's like driving your car all day and night and never stopping to change the oil.

So what does this have to do with fat burning? Wouldn't an inefficient engine be ideal if weight-loss is the sum game? Don't we want to be a gas guzzling Hummer?

If only it were that simple...

Your body stockpiles calories in 2 ways: in glycogen in your muscles and liver, and as fat, which is stored in all the places you can pinch.

The glycogen calories are quick-burning and always ready, while your fat is the slow-burning, saved-for-a-rainy-day calories.

Using your groceries as an example: You're glycogen is a bowl of fresh strawberries--instant food, while you're fat is a can of dusty chickpeas in the back of your pantry.

So how do you get your body to use the stored up fat?

The same way I get you to use the can of old chickpeas, by taking all other energy sources (food options) away.

That one beautifully simple constant to weight-loss--creating a caloric deficit, is accomplishing that. When your body needs more energy than it's been given, it starts tapping into your storage, burning your fat for energy. Intermittent fasting simply gets your body to do that sooner.

Let me explain: When you wake up, your body starts looking for energy to burn to power up your arms and legs, so it goes straight to all the quick-energy ready and waiting in your glycogen. (You store about 1500-2000 calories there.)

But then you eat breakfast--oatmeal, a bagel, smoothie, whatever.

And now your body has a NEW source of glycogen to burn--breakfast!

So it stops using what's stored up and switches to this new stuff.

Your body is thinking, “Why would I eat this dusty can of old chickpeas if there's fresh fruit available now? That fruit's going to go bad sooner too so let's eat the strawberries and stick these chickpeas back in the pantry. What's another few days or months? It can wait.”

By eating, you basically ran out to the store to buy new groceries, rather than suck it up and eat what was in your cupboard.

And if you don't completely zero out your pantry before you go shopping, or take care to only buy EXACTLY what you need down to the last tablespoon of tomato paste, that's exactly how you end up with an overflowing pantry, or excess body fat.

Your pantry and belly are the same here: it's all food you took in and didn't use yet.

To lose weight you have to stop the overbuying and duplicate purchasing.

Day after day you do this with eating all the time. Yikes!

Here's the good news: By intermittent fasting, you can burn more glycogen and consequently, use up the fat stores sooner.

It's like deciding you're not going to the grocery store and immediately replace the food you used. Instead, you decide you won't buy anything until exhausting what's in the fridge and then use up whatever is in the pantry.

Now maybe you really appreciate the futility of a pantry challenge!

And you're wondering about snacking late at night, yes, it is also refilling the supplies. It's the literal midnight run to the convenience store down the street. The more research I read, the more I realize it's not the time of day that causes the weight-gain. It's the constant resupply. It also doesn't help that the foods people eat at night often tend to be high calorie bombs that are more easily absorbed because they're super processed.

Now I get to be controversial: A lot of people assume I'm anti-exercise. For the record, I'm not against physical movement in and of itself. I simply recognize that it's a lot easier to control caloric input for weight-loss than it is to create deficiency with caloric output.

Zinczenko has a great statement in The 8-Hour Diet about this (he agrees with me). He says

“It would would take a 155-pound man 15 minutes of jogging to burn off a Twinkie. Which is a lot of time to burn off something you ate in less than a minute.”

It's too difficult to create the necessary caloric deficit required for weight-loss with exercise, especially if you are overeating, eating highly absorbent foods, and/or have stored calories a.k.a. Excess fat already.

It's so much easier to create that deficit via your diet, and IF can help you double down on that investment!

And if you still need more convincing that eating less frequently is a good idea, consider this: It's only in our very recent history that humans have had such glorious access to an abundance of food. Eating three meals a day is a habit exclusive to the developed world and in a lot of developed countries, like France for example, “snacking” is still not really socially acceptable. That's a very American thing, which I'm sure we can trace back to marketing endeavors.

There's also new revolutionary research (beyond Wrangham's energy theory of cooking), that says humans are evolved to eat only a few hours per day, AND that all this constant eating is yet another reason why we're so obese.

How a Lightbulb Makes you Fat

Take a look at a NASA-NOAA satellite night map. Most of the map is dark, but you see big, bright lights in cities like New York or Tokyo. While looking at these maps, Satchidananda Panda PhD realized where there are more lights, there is more diabetes.

Dr. Panda doesn't just mean more diabetes cases, because that makes sense. There's more people in cities so there is more of everything.

Dr. Panda means more in proportion. More risk.

His theory is that the advent of artificial light led to an artificial extension of our feeding times.

For most of human history, humans didn't have light. We had fire, true, but most humans couldn't afford to use fire after sunset because it exposed them to predators. It's only in the last 50 years that we've had light at night.

Now, I know what you're thinking… only 50 years? That can't be right. I thought so too and fell down a rabbit hole on this history of the light bulb. There were lamps and bulbs in the 1930's, but it wasn't until the 1940's that fluorescents entered the picture, and this matters because fluorescents lasted about three times longer which promoted more usage.

The rapid adoption of linear fluorescents can be attributed to the need for energy-efficient lighting in American war plants. Then another energy shortage, the 1973 oil crisis, caused lighting engineers to develop a fluorescent bulb that could be used in residential applications.

In 1976, Edward Hammer at General Electric figured out how to bend the fluorescent tube into a spiral shape, creating the first-ever compact fluorescent light (or CFL). After few design changes, early CFL's hit the market in the mid-1980's.

(I'm just old enough to remember the big and bulky bulbs of the 1990s and how often they didn't fit well in our lamps. Now in 2016 we have LEDs and all kinds of super bulbs.)

I'll stop myself here. If you want to learn more about the history of the lightbulb, go here.

So 50 years of night lights...

...and interestingly, 50 years ago is when first saw rise of weight problems.

Dr. Panda theorizes that artificial light led to an artificial extension of our feeding times, which interferes with our circadian rhythms.

If you've ever been camping, that was probably the only time you've ever been truly in tune with your circadian rhythm… if you got up and went to bed with the sun, that is.

There's a natural stop sign with eating built into our circadian rhythms, but most of us run through it every day by eating later because we had to commute home, or workout, etc. before we ate.

Delayed eating, he says, throws off our digestive system as well as the hormones and enzymes that manage it, which means you don't process and use the consumed energy as efficiently, which means more storage.

Dr. Panda believes not following our circadian rhythms, and reducing our fasting time between meals, is a contributing cause to obesity and diabetes.

If you're looking for another reason to batch cook the meal plans, I think this is a good one.

It's too tiring to cook after a long day anyway, but the sooner you can eat, meaning the sooner you can start that fast, or the closer you can live to your circadian rhythm, the better. So batch cook your meal plans guys!

Dr. Panda also does a lot of research with mice. In one study, one group of mice were given the freedom to eat anything they wanted 24 hours a day. The other group had the same freedom, but only for 8 hours. The study lasted 100 days.

The 8-hour mice looked normal but the 24-hr mice were practically twice their size.

This makes me think back to what my husband said in the last episode. He believes IF works simply because your head isn't in the trough as many hours per day, and I do think that is definitely part of it.

Closing the window of opportunity to take in calories does make it easier not to overeat and create that deficit needed for weight-loss, though now I'm wondering about appestat.

Remember? from the first episode? When I talked about how I became an overeater simply because I developed a habit of eating a lot of volume?

This next part is for my fellow overeaters:

Dr. Panda further divided the mice, giving some of the mice a diet that was higher in fat. The mice who ate a healthier diet stuck to their normal eating pattern but the mice on the high-fat diet tended to expand their eating time, nibbling all day and night.

And just to throw a human study in the mix, in 2011, researchers followed the eating habits of 100 normal-weight and 280 obese participants for 2 weeks. In both groups, the more calories someone ate at breakfast, the more total calories they ate for the rest of the day. If they ate a smaller breakfast or no breakfast at all, their total intake was less.

{Side bar: Have you ever thought about the word “breakfast”? It's literally break-fast.”}

I'll end this post with one of Zinczenko's analogies that brings all this information to life.

He compares the human body to an office building, saying:

“Most people go into the office during the day, work for 8 hours, and go home. Then, at night, the janitorial staff comes in to clean up the trash and repair the damage. The human body operates most efficiently on the same schedule; we just don't let it… A huge part of food isn't just nutrition; a lot of it is toxic, things our body doesn't need. And our stomachs and liver have to break them up and send them out. It's a huge amount of work, and it's causing a lot of damage to our system. The stomach lining has to regenerate once a day, and that happens in the middle of the night.”

I'll be back next week talking more about how environmental changes, such as our light bulbs, have led to obesity and what we can do about it.

{Side bar: I've been dying to say this since I started this new podcast: your brain is a pig. A total glycogen glutton. Although your brain is only 2% of your body weight, it demand 20% of your BMR.

If you ever got really hungry writing a book report or felt hungover after a big exam, now you might understand why. If this fascinates you, I've included a link to an article titled, “Does Thinking Really Hard Burn More Calories” by Scientific American in the show notes on below.}

Download your free research-based 7-day meal plan at and leave the guesswork and science to me.

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