Photo by Google Gemini / Olaf Kock · License: Public Domain
The Preferred Fuel
Published
Here’s another point where inverting the usual framing is more helpful than
the standard narrative. Let’s frame it around the question: “Which fuel does
the body actually prefer?”
In carbohydrate metabolism, the body uses glucose, its most important energy
source. Excess glucose is also stored as fat. When glucose runs short, the
body switches to fat metabolism and taps into its fat reserves so that our
cells can keep working.
And in the DGEDeutsche Gesellschaft für Ernährung - German Nutritional Society, a largely government funded NGO, designated as appointed authority on nutritional matters
Fat Guideline
(2), fat metabolism
(ketosisMetabolic state in which the body burns fat rather than glucose for fuel. Characterised by a measurable level of ketone bodies in the blood. → more
) is described as a
metabolic imbalance or - in the german version - derailment:
At the same time, biomarkers for the supply of essential nutrients and
metabolic imbalances (e.g. ketone bodies) must be observed.
Does That Already Answer the Question?
Both statements sound as though the body burns carbohydrates first, and only
then fat. That’s true - but it easily creates the impression that
carbohydrates are preferred, and therefore need to be replenished to avoid
slipping into emergency mode, the “derailment”.
I’ll take my usual approach of reversing cause and effect. To illustrate, let
me bring in another fuel that doesn’t usually feature in this discussion:
alcohol.
Alcohol is a toxin. It can be burned (alcohol is not calorie-free). When
alcohol is present, it is metabolised preferentially - but naturally not
because the body prefers this toxin. It has to be broken down as quickly
as possible.
Only then does the body turn its full attention back to carbohydrates. And
carbohydrates, much like alcohol, are not entirely harmless: we know
chronically elevated blood sugar as diabetes (though there are other lenses on
that too - more in a later article), and it is not healthy. The more sugar
available, the more
AGEs can form
in the body.
Only when blood sugar is low enough that it can no longer cause significant
damage does the body turn to fat. Sugar is therefore not the preferred
fuel - it’s the one that causes more damage when in excess.
The Answer
The preferred fuel for nearly all cells in our body (3) is fat. The
body simply prefers to deal with toxins first, before returning to normal
operations.
Example: a very lean person weighing 80 kg with 10% body fat has 8 kg of fat
stored - around 56,000 kcal (4). Carbohydrates account for roughly
2,000 kcal. That’s hardly a convincing argument for a preference…
Photo by Google Gemini / Olaf Kock
License: Public Domain
Relationship of so-called 'Reserve' (Fat) to actual fuel content (Carbohydrates) in wrong proportions, but closer to reality
It does no good to give overweight people the constant impression that
fat-burning is the body’s emergency mode: it is the default. It’s just
a mode that becomes hard to reach with excessive carbohydrate intake
and constant snacking.
Let me return to the DGE quote above to close, because it takes some nerve as
a nutrition nerd to question a professional society…
The only explanation I can think of is that someone confused “ketosis” (a
normal metabolic state in which the body primarily burns fat) with
ketoacidosisDangerous Metabolic state in which both very high blood sugar and very high ketone level appear at the same time. Typically observed only with type 1 diabetes. Not to be confused with ketosis. → more
- which could
genuinely be called a metabolic imbalance or even derailment.
If ketosis were a derailment, I would by now have been living with a derailed
metabolism for nearly 14 years - in which case I’d be curious to know when
the adverse effects are typically supposed to kick in.
