Fasting Zone Tracker

What's happening: Your body is actively digesting your last meal. Insulin levels are elevated as nutrients are absorbed from your gut into the bloodstream. Blood sugar rises, and your body is primarily using glucose for energy.

Key biomarkers: Insulin is high, blood glucose is elevated, and your metabolism is in storage mode — any excess energy is being packed away as glycogen or fat.

How you feel: Satisfied, energised from your meal. You may feel slightly sluggish if you ate a large or carb-heavy meal.

What's happening: Digestion is winding down. Insulin levels begin to drop, and your body starts tapping into glycogen stores (stored glucose in your liver and muscles) for energy. This is the transition away from the fed state.

Key biomarkers: Insulin is falling, blood sugar normalises, glycogen is being broken down (glycogenolysis). Glucagon starts to rise, signalling your body to release stored energy.

How you feel: Generally normal. Some people start to notice the first hints of hunger, especially if they ate a lighter meal.

What's happening: With glycogen stores becoming depleted, your body increasingly turns to fat as its primary fuel source. Fat cells release fatty acids into the bloodstream, which are then broken down through a process called beta-oxidation.

Key biomarkers: Insulin is low, growth hormone begins to rise (helping preserve muscle), and fat oxidation rates increase significantly. Norepinephrine also increases, boosting alertness and metabolic rate.

How you feel: You might experience a wave of hunger that often passes. Many people report increased mental clarity and a subtle energy boost as the body adapts to fat burning.

What's happening: Your liver begins converting fatty acids into ketone bodies (beta-hydroxybutyrate, acetoacetate, and acetone). These ketones serve as an alternative fuel source for your brain and muscles. This is the hallmark of fasting-induced ketosis.

Key biomarkers: Blood ketone levels begin to rise measurably. Insulin is at baseline. Growth hormone can be elevated 2–3x above fed levels. The cellular recycling process known as autophagy is beginning to activate.

How you feel: Many fasters describe a sense of calm focus and sustained energy. Hunger often diminishes paradoxically. Some people notice a slight metallic taste or fruity breath (from acetone).

What's happening: Ketone production peaks as your body becomes fully fat-adapted for the fast. Autophagy — the process by which cells clean up damaged proteins and organelles — is now actively under way. Your body is in a deep state of metabolic switching.

Key biomarkers: Blood ketones reach their peak levels (typically 1–3 mmol/L). Growth hormone may surge to 5x baseline levels. Inflammatory markers like IL-6 and TNF-alpha begin to decrease. BDNF (brain-derived neurotrophic factor) increases, supporting brain health.

How you feel: Most experienced fasters feel clear-headed and energised. Physical hunger is often minimal. You may notice enhanced focus and a sense of lightness. Some people feel slightly cold as metabolic rate shifts.

What's happening: Autophagy accelerates significantly. Your body is in a sustained state of cellular renewal, breaking down and recycling damaged components more aggressively. Immune cell regeneration begins — old white blood cells are broken down and new ones are produced.

Key biomarkers: Autophagy markers peak. Insulin-like growth factor 1 (IGF-1) drops, which research associates with longevity benefits. Stem cell activation begins in the gut and immune system. Ketones remain elevated and stable.

How you feel: Varies greatly between individuals. Some feel exceptionally clear and energetic, others may feel fatigued. Electrolyte balance becomes important. Extended fasts beyond 24 hours should be approached with care and ideally with medical guidance.