Metabolism 101

The "fuel tank" fallacy

VIV Research
September 20, 2021

It’s common to hear the phrase “breakfast is the most important meal of the day.” It also has no basis in fact. However, it is a good illustration of what we at VIV would call the “fuel tank fallacy” – the idea that people need "fueling" in the same way that, say, a plane or a car needs fuel.

According to this flawed metaphor, people need to eat food just before they do an activity, or else they'll run out of energy – fuel – before they complete the activity. The idea here is that the human body is like a plane or car. Just before a trip, a plane fills up with fuel, and is able to take off – but if it runs out of fuel mid-flight, it falls out of the sky.

Luckily for us, the body is not like that at all. We rarely run out of energy and come to a total standstill at random points of the day (which would be very inconvenient, as well as quite dangerous). Our physiology can very effectively decouple the energy intake and the energy utilization processes.

Looking at the blood glucose level of an individual during a day, using VIV, you will see it dip down for a while, and then, as the body taps into stored resources, it comes back up. Overall, the body regulates it around a tightly controlled band.

But without food, how does BG rise?

The difference between a human and a mechanical vehicle running off gasoline or kerosene is that the human body does not just consume food and immediately use it, as is, but it can store it for later, and also make its own glucose, through the process of gluconeogenesis. Imagine a plane that has not just its standard fuel tanks, but also has a backup supply of fuel in the form of crude oil barrels, plus a mini-distillery and refinery, fast enough to keep the plane in the air if the regular fuel tanks are empty.

As a simple demonstration of the fallacy, VIV Chief Research Officer Tony Martin did something many people would be surprised is possible. In a single day, he:

  • Fasted – with no food intake, only water – for the entire 24-hour period
  • Slept from hour 0 to hour 6
  • Worked, exercised and went about daily life from hour 6 to hour 16
  • Strenuously exercised during hours 16 to 24, including a long hike, and climbing the tallest mountain in Ireland, Carrantuohill, then doing pull-ups at the top

During this day of fasting, his blood glucose level fluctuated to some degree, but stayed generally within the VIV Zone of 4.0 to 6.5 Mmol, despite the complete absence of energy intake – 0 calories consumed. 

Without any food or caloric intake, his body was able to generate the energy it needed, even for a strenuous day of activity, entirely through the internal process of gluconeogenesis – making its own glucose. Despite this lack of “fuel” the plane didn’t fall from the sky.

This flawed metaphor is responsible for a huge amount of erroneous thinking about how, when and why people should eat. With VIV, it’s possible to look inside the body, and understand what is really happening in terms of energy utilization and “fuel,” then finally lay the fuel fallacy to rest.