Eight people. 100 miles. Five days. Zero calories.

A five-day endurance experiment exploring what happens when the body shifts from carbohydrate towards stored fat as its principal source of fuel.

The Route

From Henley on Thames to Bristol following the River Thames and Kennet & Avon Canal.
The project took place from 19th to 23rd September 2020.

The Task

Eight people, including two with Type 1 diabetes and Olympic athlete James Cracknell, set out to cover 100 miles over five days between Henley-on-Thames and Bristol — while consuming zero calories.

The Zero Five 100 project was conceived by Dr Ian Lake, a GP living with Type 1 diabetes, to explore what happens when the body is asked to sustain prolonged endurance exercise without dietary energy.

The participants prepared by training for both the daily distances and periods of fasting, with most already adapted to a ketogenic diet before the challenge.

The aim was not to establish a new way to exercise, or to encourage others to repeat the experiment. It was to explore a physiological question under deliberately demanding conditions:

Could the body draw on its own stored energy to sustain five consecutive days of endurance exercise — and what would happen in people with Type 1 diabetes?

The Team

Steve Bennett, Businessman (Primal Living).
Dr Ian Lake, GP with Type 1 Diabetes.
Dr Trudi Deakin, Dietitian.
Dr Ali Ibrahim, Consultant Psychiatrist.
Gayle Gerry, NHS Practice Nurse.
Jon Furniss, Engineer with Type 1 Diabetes.
James Cracknell, Olympic Athlete and Journalist.
Jake Thompson, Businessman on a ketogenic diet weight programme.

All participants were physically and mentally fit, well nourished and prepared for the challenge. Training included both fasting and covering the distances required each day.

Every participant was free to stop at any point.

All eight completed the project safely.

Important: Zero Five 100 was an experiment in metabolic performance. The team does not advocate that others undertake a similar project, nor suggest that prolonged fasting combined with endurance exercise is an optimal or desirable activity.

Fasting in a well-nourished individual is also physiologically different from starvation associated with nutritional deficiency and malnutrition.

Those ideas ultimately became part of the thinking behind Shifting Gears.

Sometimes, to understand a familiar system differently, you have to change the conditions and see what happens.

Rationale

The human body can obtain energy from more than one fuel source.

Glucose can be used immediately or stored as glycogen. Fat provides a much larger reserve of stored energy. When carbohydrate availability falls, insulin levels reduce and the body increasingly mobilises stored fat. Fatty acids can then provide energy directly, while the liver produces ketones that can be used by a number of tissues as an alternative fuel.

This shift in fuel use is central to nutritional ketosis.

For someone with Type 1 diabetes there is an additional and important question.

Without sufficient insulin, elevated ketones can occur alongside uncontrolled glucose production and develop into diabetic ketoacidosis (DKA), a dangerous medical emergency.

But nutritional ketosis and diabetic ketoacidosis are not the same physiological state.

People with Type 1 diabetes still require insulin when fasting or following a ketogenic diet. The interesting question is what happens to glucose, ketones and insulin requirements when carbohydrate intake is greatly reduced while sufficient insulin is maintained.

Zero Five 100 provided an opportunity to observe this under deliberately demanding conditions.

The project combined prolonged fasting with five consecutive days of endurance exercise. It was intentionally outside normal daily experience — not as something for others to reproduce, but as a way of making the underlying metabolism easier to observe.

If the body could continue to perform while consuming no food, where was the energy coming from?

Project Results

We investigated and demonstrated the following:

The two participants with Type 1 diabetes completed the five-day challenge while continuing to use insulin. As carbohydrate availability fell and fat utilisation increased, their insulin requirements changed substantially. The project also illustrated an important distinction: producing ketones through nutritional ketosis is not, by itself, diabetic ketoacidosis. For people with Type 1 diabetes, insulin remains essential, including during fasting or nutritional ketosis.

Breath metabolic testing and blood ketone measurements showed substantial fat utilisation during the challenge. Participants were able to continue exercising over successive days despite consuming no food, demonstrating the body's ability, when appropriately adapted, to draw upon its stored energy reserves.

Continuous glucose monitoring provided a detailed picture of glucose throughout the project. The body does not depend entirely upon dietary carbohydrate to maintain blood glucose. The liver can produce glucose through processes including gluconeogenesis and glycogenolysis. This is particularly important when thinking about Type 1 diabetes because dietary carbohydrate, liver glucose production and injected insulin all contribute to the glucose concentration we eventually see on a CGM.

The Human Experience. There were also observations that were harder to quantify. Participants commonly reported good mental clarity and surprisingly stable energy despite the combination of fasting and prolonged exercise. There was some minor musculoskeletal discomfort, as might be expected during a 100-mile challenge, but all eight participants completed the project.

Re-Thinking Diabetes

Zero Five 100 began as an experiment in fasting, exercise and metabolic performance.

But it led to a much bigger question.

What if Type 1 diabetes management is not only about correcting glucose, but about understanding what creates the glucose and insulin requirement in the first place?

Carbohydrate intake, liver glucose production, exercise, stored fuel and injected insulin all interact.

Changing one changes the others.

WATCH ZERO FIVE 100

Follow the team through five days, 100 miles and zero calories — and hear from the people who took part.

Watch the movie

THE SCIENCE BEHIND ZERO FIVE 100

Zero Five 100 was more than an endurance challenge. It was designed to examine what happens during prolonged fasting and exercise when the body is relying predominantly on stored fat for energy.

The project included participants with and without Type 1 diabetes and generated physiological data throughout the five-day, 100-mile challenge.

The findings were subsequently published as a peer-reviewed medical paper:

Nutritional ketosis is well-tolerated, even in Type 1 Diabetes: a proof-of-concept study

Read The Medical Paper

Published in Current Opinion in Endocrinology, Diabetes and Obesity, 2021.

Zero Five 100