What happens during fat loss: A brief dive into the good stuff

It's not uncommon, and in fact pretty typical, that people think of the word "burning" when they think of fat loss.

"I'm burning calories"

"You need to burn that off"

"Feel the burn"

In this way, our relationship with fat loss is one we are convinced we need to "feel" and because of this exercise is often the first avenue people choose to lose fat.

I've beaten the idea down more time than I can remember but the reality is that exercise doesn't really burn that many calories.  At least not enough that the average person with plenty of other things to do in their life could create a substantial and sustainable calorie deficit from.  Plus, the idea of "burning off" calories during exercise then shifts the focus on exercise solely as a means to get leaner and not to get stronger, more resilient, stable and mobile.

Lets change that.

When You Eat Less

There are two major enzyme  complexes associated with calorie status: mTor and AMPK. mTor is associated with anabolism (or building up) so we're going to focus on AMPK

Lets jump back to calories quickly - you probably know that we get calories from the food we eat.  We digest and assimilate foods to derive energy from them.  But instead of thinking of different "fuels" like carbs, fats or proteins, there is only one TRUE fuel of the body: ATP.  ATP is what ALL food (whether it's protein, carbs or fats) is oxidized by your cells into.  There are different pathways that each macronutrient can take but the end result is always ATP.  And it is looked at as the energy currency of the body for that reason.

So if all food, no matter the source, is essentially turned into ATP and that ATP is what actually gives us "energy", then what happens where there is less coming in than usual?

Glad you asked.

What the brain does

Your hypothalamus is a small portion of your brain with a few very important neuronal networks.  The hypothalamus is sensitive to hormones released by fat cells and the digestive tract which help it coordinate feelings of hunger, satiety, fullness and so on.  In essence, your hunger is dictated by more than just how full your stomach is.  The nervous systen works with other systens (like the digestive system) to help sense your calorie intake to maintain homeostasis. 

What AMPK does

Along with hormones that tell the hypothalamus what your calorie intake is like, when ATP is low (which, remember comes from the calories we eat) AMPK is upregulated.

So the body senses low ATP and AMPK rises  - this enzyme complex will do things to raise and preserve ATP.

This is where fat loss comes in and why low energy states are required for losing body fat and even improving cell health.  When AMPK rises, it will:

-Increase glucose transport into cells 

-Shut down the creation of new fatt acids

-Break down existing fatty acids

-Increases autophagy of old low functioning mitochondria

-Increases biogenesis of new mitochondria

In laymans terms, AMPK helps drive more glucose into your cells, inhibits fat storage, promotes fat "burning" (there it is!!), recycles old mitochondria and upregulates the ability of new mitochondria to oxidize fuels.

Why this is important

We need low energy states like this because you can see that it not only keeps us from storing more fat but it causes us to use the fat on our bodies for energy, thus getting us leaner.  In addition, our insulin sensitivity likely increases from the upregulation of glucose transporters. And finally, recycling old mitochondria and upregulating our mitochondrial health means our ability to get lean and stay lean improves. Our ability to use the food we eat for fuel improves.  Kind of a win-win:)

You might remember from a few posts ago here where I talked about obesity and inflammation, how poor mitochondrial health creates a Catch-22 where getting obese causes inflammation and that inflammation impedes our ability to get lean.  But we can see that low-energy states not only get us leaner but improve those inflammation markers.

But all of this is not an attempt by the body to get you beach-ready.  Instead it is a physiological adaptation to make sure there is enough energy to function which is why you release fatt acids from fat cells to create more ATP so the body has energy.  And your cells become more insulin sensitive so they can uptake glucose and make ATP.  And the mitochondria improve their function so they can be more efficient with fuel use to again, improve the ATP availability in the body.  But for you, it might just mean that it helps you get beach-ready at the same time!

Where most people screw it up

This is really just a brief snapshot.  But you can see the tip of the iceberg in adaptations the body is making you ensure you don't whither away and die. And there are rate limiting steps in how fast you can lose body fat, not nearly the same limit as BUILDING muscle but still, a limit.  Which means dieting too hard or too long comes with consequences.

AMPK also downregulates protein synthesis.  Protein synthesis is a very energy costly process and building muscle (which is the synthesis of new proteins) becomes a low priority when in a fat loss state. It doesn't mean it can't be done but it does mean on average at least a 15% reduction in anabolism and likely more with longer and harder dieting.

So an extreme diet for the average person usually just means stagnation in training or possibly some muscle loss. And if you tend to crash diet then rebound, the signals you are sending your physiology are those of extremes.  It's either way too little ATP or way too much ATP and there is no chance to come back to center and find a balance. What that means for the chronic crash dieter is experiencing all the extremes of those physiological states without much of the benefit.  Too harsh of a diet means a crashed metabolism and sky-high cortisol and inability to make gains in training - bingeing means no added bump to muscle building but lots of added fat gain and decreased insulin sensitivity. Then it's back to the other extreme.

What you want to do is find that fat loss window where you can still train, sleep and manage your day while experiencing some hunger.  Hunger is inevitable as the hypothalamus is sensing lower energy and trying to tell you to eat more.  In essence, feeling hungry means you're probably burning (there it is again!( some fat. But faster and harder doesn't mean better progress. As you diet, your metabolism will slow, training won't be as good and mentally you might feel you need a break, maybe sleep starts to become interrupted or you feel burned out.  So the thing to do here is come back to baseline and maintain.  You need 24-72 hrs back at maintenance to see a cessation of the negative effects of dieting.  But remember, bingeing doesn't improve that situation even more, maintenance will do just fine.

Some people choose to do a week or two at maintenance to come back refreshed and restored, ready to enter a fat loss phase again while others choose a slightly longer fat loss phase with 1-2 maintenance days each week instead.

What this really is

From what you've read above, the ultimate factor here is energy intake and the desire by the body to have enough ATP to perform all of it's functions. Fat loss, fat gain, muscle loss, muscle gain are all products of ATP availability and signals we send our physiology.  Instead of thinking of just "burning things off" think of getting leaner as a process and adaptation your body needs to make to help you still live and function despite fewer calories - so hammering yourself with loads of exercise or starving yourself impedes your ability to function properly while also providing little to no benefit to the speed at which you lean out.

I present this for one reason: instead of trying to argue or reason with a person, just look to the science.  Look to your physiology and once you understand what is happening it becomes clear why you would want to do things the right way.  And of course there are times for pushing the limit and stepping on the gas pedal but remember that that always comes with side effects and consequences - those of which the average person is not prepared to deal with (which is why people hire coaches).

Find a low energy state, eat high volume foods to help you feel full even while the brain knows better and eat enough protein (about a gram per pound) to maintain your muscle mass. Whether you want lower fat or lower carbs doesn't matter as much as choosing an approach that you can maintain and function well on.  And remember that the brain senses calories, not how much your stomach stretches which is why you can't diet on bowls of raw cabbage and live on easy street. Even a buttload of broccoli isn't that many calories and the hypothalamus WILL sense whether it's enough energy or not.  This is why choosing foods that maximize satiety for YOU is so important.  At a time when you will probably be hungry it's imperative your food choices curtail that as much as possible.

This all comes down to how much ATP is available - how you approach that balance can determine your success.