“Which mode should I start with?” — a common question.
Light Keto (12-hour fast), Keto Body (16-hour), Town Courier (18-hour), Express Courier (20-hour) — HIKYAKU’s four modes are not simply “different durations.” As the fasting window extends, what happens inside the body shifts qualitatively. Once each step of the staircase is understood, the right starting point becomes visible.
12 hours: the quietness of insulin
Finish dinner, skip breakfast — or eat an early dinner and a normal breakfast. Either way, twelve hours is within reach.
In this window, the dominant event is the drop in insulin. A few hours after eating, blood glucose stabilizes; insulin returns to baseline. Fat cells switch slightly from “storage mode” toward “available for mobilization mode.”
This is the biochemical foundation of Light Keto (12–14h fasting, 50–100g carbs/day). No major metabolic shift has occurred yet, but giving insulin a daily “rest period” alone significantly lowers the risk of chronic hyperinsulinemia.
For someone new to keto, this is the first gate. You don’t need to eliminate carbohydrates entirely.
16 hours: fatty acid mobilization in earnest
Past 16 hours, liver glycogen (the body’s sugar reserve) begins to deplete. The body shifts toward active mobilization of fatty acids as its energy source.
Free fatty acids in the blood rise. The liver intensifies ketone body synthesis (β-hydroxybutyrate, acetoacetate). The brain begins using ketones too. The phenomenon described as “mental clarity” has its biochemical basis here.
Keto Body (16–18h fasting, 20–50g carbs/day) builds this window into a daily habit. With carbohydrate intake also reduced, ketosis remains stable across the full 24-hour cycle.
The path for intermediate practitioners — those bringing keto into daily life.
18 hours: autophagy awakens
Past 18 hours, another cellular system activates — autophagy.
Autophagy is the cell’s internal recycling mechanism, breaking down and reusing damaged proteins and organelles. When nutrients become scarce, it activates — an evolutionarily conserved survival strategy. Yoshinori Ohsumi received the 2016 Nobel Prize in Physiology or Medicine for elucidating this mechanism.
When autophagy intensifies, the cell undertakes internal “housekeeping.” Aged mitochondria are broken down, and synthesis of new mitochondria is promoted. This is sometimes called “cellular rejuvenation” — more accurately, “replacement.”
Town Courier (18–21h fasting, 20–30g carbs/day) carries the body into this window. Advanced keto practice, realistic deep ketosis.
20 hours: growth hormone surges
Around the 20-hour mark, growth hormone (GH) secretion surges dramatically. Some studies have reported increases of over 2000% during a 24-hour fast.
Growth hormone is responsible for fat oxidation, muscle maintenance, and tissue repair. The reason muscle is preserved during fasting is this mechanism.
Norepinephrine also rises, keeping energy expenditure elevated. A metabolic state that is “burning while preserving” — an evolutionarily refined design.
Express Courier (20–23h fasting, under 20g carbs/day) takes the body to this deepest point. The strictest practice, the path for advanced and “arrived” practitioners.
Modes are not “where you are” — they are “the wave”
A common misconception to clear here.
The four modes are not a staircase where higher equals better. Rather, each step has a duration and purpose for which the body should stay there.
- Light Keto can be sustained for life — suitable as a baseline
- Keto Body is deep keto as everyday practice — realistic for working adults
- Town Courier is a few times a week for deeper exploration — for advanced practitioners
- Express Courier is a few days a month to fully reset — total reset days
As discussed in the mTOR scale (→ separate article), longevity research suggests the target ratio of 60% suppression / 25% activation / 15% neutral. This translates to a lifestyle centered on Keto Body or Town Courier, with sufficient protein and exercise on activation days.
In other words: “Always Express Courier” is not the right answer. Cycling between the four modes — drawing a wave across the year — is the essence of longevity.
A path for today’s body
Choosing among the four modes is straightforward.
| If you… | We suggest |
|---|---|
| Have never tried keto / want a daily practice | Light Keto |
| Already fast 16h, want to go deeper | Keto Body |
| Want to seriously pursue ketogenic metabolism and autophagy | Town Courier |
| Want a few deep-reset days per month | Express Courier (combined with other modes) |
The body is not a fixed machine. The mode you need yesterday and today can differ. HIKYAKU’s mode setting is switchable anytime in settings.
To live cleanly and beautifully is, perhaps, to hear today’s voice of your body, from among four available paths.
This article is for informational purposes and is not medical advice. Consult a physician before beginning extended fasting. Those who are pregnant, breastfeeding, or have diabetes or eating disorders should consult a physician before practicing fasting.