You’re Using Carbs Right Now (more than likely)

It would be cool if we could know when we are using one over the other because we could tailor our life to be optimized in such a way.

For example…

When we’re burning carbs, it would be great to go run some sprints or hit the bike for a bit.

When we’re burning fat, it would be awesome to use our brains more to capitalize on that fuel source or maybe go for a walk to torch more of it off our bodies!

Knowledge is power, and if we know what we’re burning, we can do a lot more with it. So here are a few ways to know WHAT fuel you are burning.

1) Simple… You ate carbs within the last couple hours
This one seems like it goes without saying…

But if you had carbs inside of two hours, I don’t care how much you think you’re in ketosis, you’re probably burning carbs at this point in time.

Before the body can start utilizing fat as a fuel, it first has to burn through available glucose.

Nothing makes glucose more available then eating carbohydrates… and it takes time to burn them.

2) You Can Test If You’re Burning Carbs or Fat By Monitoring Breath Carbon Dioxide

This one is a bit newer, but there is a device that measures the CO2 in your breath to tell you on a scale of 1-5 how much you are burning in the way of either carbs or fat.

It’s not designed to make you feel bad one way or the other. It’s designed to help you know where your body is at a certain point in time. It’s for metabolic flexibility.

The device is called LUMEN. It is pretty unreal. Its not like a ketone meter. It’s not measuring breath acetone so much as it is levels of CO2.

The thing I like about it is that it is very user friendly and not an advanced tool. I find, for most of my audience, it is a great tool to have because it is so simple and cuts out the noise.

Dr. Mark Hyman as well as some Gold Medalist and Tour De France Champions have been endorsing it as well.


For me, it’s nice to know when a workout was SO TOUGH that I started burning carbs. Or it’s nice to know that the fasting that I have been doing has gotten me deep into a fat-burning state.

OR, it’s nice to know that I am metabolically flexible and burning BOTH at a given point in time. Then I work backwards from there and figure out what I should make a lifestyle habit.



3) Peaks and Troughs in Energy
This is a common one if you’re a carb burner.

And at first, this sounds negative, but it’s not meant to be.

When you’re burning carbs, you can expect a nice, strong surge of energy that can actually be very beneficial. But when you burn through that fuel, the post-surge is called a trough.

This is where you get fatigued and bonk faster. It’s a smaller fuel tank with faster burning fuel compared to fats/ketones where we have a LARGER tank of a slower burning fuel.

Another reason that carb burning makes you feel tired is Tryptophan.

We know that when you spike insulin levels, it binds to cells and basically breaks the door down so other molecules can enter.

Specifically, large-neutral amino acids (LNAAs) can enter muscle cells more easily thanks to insulin opening the door for it.

Tryptophan is an amino acid that enters the brain to eventually be converted to our sleep hormone – melatonin. However, it usually has to fight very hard with other aminos to be accepted by its receptor to cross the blood-brain barrier.

Since insulin causes other aminos to uptake into muscle cells, tryptophan does not have to fight as hard as usual and has easy passage into the brain to produce melatonin and cause sleepiness.

Obviously, great for sleep…. but not so great for being able to maintain consistent energy throughout the day. Not bad, not good, just what we need to consider.

4) More Hungry

There was a study in the International Journal of Obesity that looked at the effect of carbohydrate ingestion on hunger and satiety.

A simple carbohydrate meal, where more carbs are burned in a shorter timeframe, was associated with greater hunger at every time point after meal ingestion (30, 60, 90, 120, 180, 240 mins).

This increase was statistically significant at 60 and 180 mins. Following a simple carb breakfast, satiety was lower at every time point than for a complex carb breakfast, and significantly lower at 30, 60 and 90 mins.

So, it seems that burning carbohydrates, particularly high GI carbs, can increase hunger and make you feel less full in the short-term. When you burn carbs and get that sharp spike in insulin, the crash in blood glucose can leave you craving more food.

5) The Brain…. Fats (ketones) provide a more STABLE Network Stability

Ketones are a more efficient brain fuel than glucose as they provide more energy per oxygen molecule utilized.

When looking at the literature in this area, a study in Proceedings of the National Academy of Sciences of the United States of America looked at how diet influences brain network stability (basically how the brain regions communicate with one another).

42 adults had their brains scanned by fMRI while under either a standard diet, overnight fasting or a ketogenic diet.

Another overnight fasted cohort was used, however, they were scanned before and after ingesting either a glucose or exogenous ketone ester bolus.

Interestingly, the researchers found that “networks were destabilized by glucose and stabilized by ketones, irrespective of whether ketosis was achieved with a ketogenic diet or exogenous ketone ester“.

Ketones both increased overall brain activity and stabilized networks, which was defined as the ability to modulate sustained functional communication between brain regions.

The main part to focus on this study here is the fact that glucose de-stabilized the brain in comparison.

So, although it could be highly subjective in our own scenarios, if you start feeling foggier than usual, maybe you’re not running on the fats or ketones that you thought you were.

This is exactly the kind of scenario in which I would like to test using LUMEN and see what fuel I am actually burning.

It can help confirm my hunches and help me learn and associate more about why my body feels a certain way at a given time.

Remember, the goal isn’t to be one way or the other, it is to learn your body and learn the flexibility associated with it and WHAT THAT FEELS and also what it LOOKS like with the data!

As always, I will see you tomorrow!