Day 1 of a Longevity Fast – The Transition Phase
Amanda Hamilton has been guiding people through fasting and nutrition programmes for over 24 years. With a role at The Longevity Doctor clinic on Harley Street, she combines science-led insights with practical, real-world strategies. On her sell-out five-day Longevity Fasts, Amanda guides participants through the experience with confidence and safety, helping to ensure fasting becomes a positive and transformative tool rather than an intimidating hurdle.
The first day of a Longevity Fast is all about transition. Your body begins to move away from its usual reliance on frequent meals and carbohydrate-rich foods into a very different metabolic state — one that promotes flexibility, repair and resilience. As calorie intake drops, particularly from carbohydrates, your blood sugar levels begin to fall. In response, the pancreas releases less insulin, the hormone that normally directs glucose into storage. This is a beneficial change because persistently high insulin is linked to conditions such as type 2 diabetes and even certain cancers. Research shows that lowering insulin through fasting improves insulin sensitivity and reduces inflammation.
Inside the body, the liver begins to take on the role of stabilising energy levels. It holds a supply of glycogen — about 100–120 grams — which is usually enough to fuel twelve to twenty-four hours of normal activity. On day one of the fast, the liver begins breaking down this glycogen to maintain stable blood sugar, a process known as glycogenolysis. As these stores run low, your body prepares to shift towards fat as its primary source of energy.
This is when metabolic flexibility begins to emerge. As glycogen depletes, fat is broken down for energy, and the liver starts to produce ketone bodies, such as beta-hydroxybutyrate. Ketones are not only an alternative fuel but also powerful signalling molecules that activate pathways linked with stress resistance, mitochondrial health and cellular repair.
It is not unusual to feel sluggish during this first stage. Fatigue, brain fog or mild headaches are common as the body recalibrates and adapts, particularly if caffeine intake has been suddenly reduced. The important thing to remember is that this stage is temporary. By tomorrow or the next day, many people feel the opposite — lighter, clearer and more energised. That is the body finding its fasting rhythm, and it is worth allowing space for that adjustment.
My next blog post will cover what happens on days two and three of the Longevity Fast. Our bodies experience incredible healing and renewal. Why not join our upcoming 5 day Guided Longevity Fast (online) >> click here to find out more
