<aside> <img src="/icons/light-bulb_blue.svg" alt="/icons/light-bulb_blue.svg" width="40px" /> Put simply, consuming all of your calories in a given window of the day, usually 8 hours or less, and abstaining from calories in the remaining hours.

When you start consuming calories, you push the first domino in a series of responses that allow your body to process what you’re consuming, including rising levels of insulin, which converts the food you’re consuming into energy, ready to be used or stored for later.

The idea of fasting is to restrict this response to a small window of the day, and in doing so, your body will simply use what it already has at its disposal in the remaining hours.

Consuming Nothing vs. Consuming a Small Amount

In the Minnesota Starvation Experiment, researchers aimed to better understand the effects of hunger and starvation to help people rehabilitate and recover from starvation that resulted from World War II. 36 men consumed 3,200 calories for 3 months, followed by 1,570 calories for 6 months, these figures adjusted to their weight with the aim of losing 1.1kg per week. Participants saw a significant reduction in strength and endurance, body temperature, heart rate and sex drive. Reports claimed that the men would dream, read and talk about food, also displaying fatigue, irritability, and symptoms of depression.[1]

By contrast is the story of Angus Barbieri, who carried out the longest fast recorded to date in 1965, lasting 380 days. Angus started this fast over 200kg in weight, losing a staggering 125kg in the year-long period, consuming no calories whatsoever. This process was carefully monitored with frequent hospital visits and regular blood tests. The report states, “The patient remained symptom-free, felt well and walked about normally,” and “prolonged fasting had no ill effects.”. Angus’ weight also remained stable for years following the fast.[2] The procedural measures of these two studies were far from similar, with Angus being a single individual who initially weighed over 200kg; however, these cases sparked a great debate on the difference between eating nothing and eating not quite enough. So, what causes this contrast?

Why causes this disparity?

When you consume regular meals, you keep insulin steadily high, and in doing so, you are unable to access stored fat for energy.

You give yourself ‘just enough’ to keep your metabolism primed for burning glucose as a source of fuel, this glucose being in limited supply - in the case of the study, just a portion of the 1,570 calories consumed.

In contrast, by eating nothing, you make the switch from using glucose as a source of fuel to ketones from fat stores, with fat stores being in much greater supply - the average human carrying over 70,000 calories worth of fat on their body.

Your body will get it’s glucose whether you give it to it or not!

A finding that may surprise you from Angus’ 380-day fast was that blood glucose levels remained consistent at around 30 mg/100 ml for the duration[2], despite no consumption of carbohydrates... How could this be possible?

In the absence of incoming carbohydrates, your liver is actually capable of producing glucose from glycerol, which is produced from the breakdown of stored fat. This process is called gluconeogenesis, translating to “making new glucose”.

Having what is called ‘metabolic flexibility’ means that our body is able to use glucose and fat at the appropriate times.

This is to ensure we enter the most efficient metabolic state based on food availability, so, during the day, we are primed to use glucose as we consume food, and then in the evening, we steer towards using fat.

Intermittent fasting allows you to, almost ‘practice’, tapping in and out of the different energy stores, making you much more metabolically flexible.

This has been a practiced method for endurance athletes for some time, using fasting or fasted training to practice using both energy sources so that when the lengthy training session or race arrives, they have the greatest access to both energy sources!

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