If you caught my recent post, you likely found yourself astonished by Angus Barbieri’s ability to sustain a 382-day fast, relying solely on water, vitamins, and electrolytes. My longest fast lasted only three days, and it’s truly mind-boggling to consider how he managed to sustain such a state for over a year.
Angus hated the fact that he was obese and decided to work towards his ideal weight of 180 pounds (82 kg). His own doctors didn’t believe that he would last that long, but to their surprise, he did. In a press conference after his fast, he said:
It went down okay. I feel a bit weak, but I thoroughly enjoyed it.
A ton of questions riddled my mind when I first read about Angus’ fast.
How was it possible for a person to survive over a year without any food?
Wouldn’t the body start breaking down and eating away at itself after a certain point?
How did he avoid life-threatening complications like organ failure, severe muscle wasting, and extreme nutritional deficiencies?
What drove him to attempt such an unusually prolonged and dangerous fast in the first place?
I was fascinated by this extreme case that surpassed my understanding of Biology and the body’s nutritional needs. The more I learned, however, the more I realized that the body employs different physiological mechanisms to preserve normal capabilities during periods of starvation or reduced food intake.
A series of metabolic changes are activated within the body when you fast. The body transitions through different phases, tapping into different fuel sources, and adjusting hormone levels to adapt during fasting.
Anabolic Phase (0-4 Hours)
During this phase, the body breaks down ingested food into nutrients (glucose, amino acids, fatty acids) that are used to provide energy to the body, make new tissue, or stored as energy for future use.
Insulin is released into the bloodstream to stimulate the uptake of glucose into body cells. Insulin levels vary depending on the macro-nutrient composition of your pre-fast meal. On ketogenic or low-carb diets, for instance, insulin levels tend to be lower as compared to high-carb diets.
Excess sugar is stored as glycogen in the liver and muscles, or as fat which acts as a long-term energy storage option.
Ghrelin, the hunger hormone level decreases and leptin, the satiety hormone level increases to signal to the brain that the body is full.
Catabolic Phase (4-16 Hours)
During this phase, the body makes use of the nutrients from digestion for energy. As your blood sugar goes down, insulin levels drop as well. This signals the pancreas to release glucagon, a hormone that stimulates the breakdown of glycogen in the liver into energy.
When the stored glycogen runs out, the body turns free fatty acids and amino acids into glucose for energy. This process, called gluconeogenesis, takes place in the liver and kidneys.
As insulin levels drop and as the body gets deeper into the catabolic phase, a cellular “housekeeping” process called autophagy gets activated.
Autophagy is derived from the Greek words auto meaning “self” and phagein meaning “to eat”. It means “self-eating”. It is the process by which cells recycle their own damaged proteins and compromised components leading to cellular rejuvenation.
Apart from fasting, autophagy be activated through other means:
- Caloric restriction directly limits nutrient availability, forcing cells to recycle components for energy.
- Exercise stresses cells, stimulating autophagy to meet increased energy demands
- Ketogenic diets shift metabolism to burn fat instead of carbs, mimicking a fasted state and activating autophagy.
Autophagy is associated with various benefits including:
- Promoting longevity and healthy aging by clearing out damaged cell components.
- Reducing detrimental inflammation by eliminating defective proteins.
- Destruction of pathogens and disease-causing agents boosting immunity.
Check out this simple illustration on autophagy to learn more.
Fat-Burning Phase (16-24 Hours)
Your body shifts to stored fat as fuel in this state. Gluconeogenesis resumes, and the body’s fat cells release fatty acids for oxidation in the liver.
Most of the glucose produced through gluconeogenesis is used by the brain while the rest of the body relies on fat fuel. Decreasing glycogen and insulin levels trigger the release of AMPK, a protein factor that accelerates autophagy.
Transition to a fat-burning state is influenced by different factors such as exercise or the nutrient composition of your pre-fast meal. During exercise, your body exhausts glycogen stores much faster, speeding up the switch to fat metabolism. Ketogenic diets reduce the amount of glycogen stores created, making it easier for the body to tap into its fat stores.
Ketosis (24-72 Hours)
Ketosis is the process by which fatty acids are converted into ketones and burned for fuel. At this point, the body relies heavily on fat for energy. The brain switches to using ketones as its main source of fuel due to depleting glucose levels.
Brain-derived neurotrophic factor (BDNF) is synthesized during this stage in the fast. It serves different functions:
- Supports neuron growth which facilitates learning and improved memory formation.
- Repairs damaged neurons helping retain brain function.
- Regulates mood. Low BDNF levels have been linked to depression.
- Some studies suggest that it could be a protective factor against age-related cognitive impairment and illnesses such as dementia.
Deep Ketosis (72+ Hours)
Ketones continue to be the main fuel source for the body and brain. Glucose and insulin levels remain low, improving insulin sensitivity and metabolic health.
Insulin-like Growth Factor (IGF-1) levels decrease, further accelerating autophagy. Lower IGF-1 signals to cells that nutrients are scarce, spurring them to recycle components.
Growth hormone is released to maintain muscle mass and lean tissues. It signals the breakdown of fat for energy further enhancing ketosis and progressing weight loss.
Health Benefits of Fasting
Intermittent or prolonged fasting routines offer various health benefits including:
- Weight loss: You eat fewer calories and break down body fat as an alternative fuel source.
- Improved insulin sensitivity: This improves your blood sugar levels reducing the risk of type 2 diabetes.
- Reduce inflammation and improve immune response through autophagy.
- Improve metabolic processes that may enhance brain function for instance production of BDNF.
- Induce cellular repair processes that offer anti-aging benefits.
- Improved mood and mental clarity due to high BDNF levels during the ketotic phase.
You don’t have to fast for 382 days to achieve these benefits. Angus was literally just built different (he had ample fat reserves to sustain him that long). He demonstrated incredible discipline in sticking to his fasting regimen and following his doctors’ advice. He even gave up working at his family’s fish and chips shop where the temptation to eat would have been too difficult to resist on a daily basis.
Conclusion
Taking a deeper dive into the body’s physiological capabilities during fasting helped me appreciate its resilience and adaptability during periods of reduced caloric intake such as fasting. Nonetheless, it is important to seek professional health advice and guidance to ensure safe practices, especially during prolonged fasting.
Stay tuned for the next post where I’ll go over my personal experience with fasting. For those of you celebrating Thanksgiving, go easy on the Turkey and pies 🙂
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