SardinesFasting
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A water fast eventually burns through lean tissue. SardinesFasting flips the same metabolic switch — glucose to ketones to autophagy — while protein and omega-3 keep your muscle and your sanity intact. Tracked hour by hour on your iPhone.
During a prolonged water fast the body eventually breaks down lean tissue for amino acids. Sardines are a near-perfect fasting food: 22–25 g of protein and roughly 1–1.7 g of EPA + DHA omega-3 per can, with very low mercury because they're small forage fish. You get the metabolic shift of a fast — with the raw material to protect your muscle.
Nutrition ranges per USDA FoodData Central for canned sardines; values vary by brand, can size and pack.
Four mechanisms do the work. Each card below states the evidence level honestly — yeast, animal, or human — and links to the paper so you can read it yourself. None of this is medical advice.
Autophagy is the cell's recycling system — packaging and breaking down its own worn-out parts. Lab and animal studies show nutrient starvation switches it on. The foundational work (Takeshige & Ohsumi, in yeast) earned the 2016 Nobel Prize in Physiology or Medicine.
Takeshige 1992 · Mizushima 2007 →Once glycogen runs low, the liver makes beta-hydroxybutyrate (BHB). Research describes BHB as more than fuel — a signaling molecule that inhibits certain HDACs and engages receptors involved in inflammation. It's why "fasted clarity" has a biochemical story behind it.
Newman & Verdin 2017 · Veech 2004 →A JAMA review found regular fish intake (~1–2 servings/week, ~250 mg/day EPA+DHA) associated with markedly lower coronary-death risk, and concluded the benefits outweigh contaminant risk for most adults. Sardines deliver that omega-3 with low mercury.
Mozaffarian & Rimm 2006 · Calder 2017 →Glucose ÷ ketones (and the related GKI) is a practical number for how deep you are in the fasted, low-insulin state. The app computes it from your logs so you can watch it fall — the same index introduced in the metabolic-management literature.
Meidenbauer 2015 →Reviews describe a shift from glucose toward fat-derived ketones that generally begins after ~12 hours and unfolds across the 12–36 hour window. The exact timing varies with your last meal, activity and metabolism. The app shows you which phase you're in, live.
Insulin is elevated from your last meal. Fuel comes from food and stored glucose.
Liver glycogen drains — reviews put depletion around the 10–14 hour mark. Mild hunger waves are normal.
The body begins favouring fat. Blood ketones start climbing (often measurable from ~8–12 hours).
BHB can reach roughly 2–5 mM by around 24 hours. This is the window the GK Ratio tracks.
Cellular cleanup signals (lower insulin/IGF-1, AMPK up, mTOR down) are most active. Mechanism strongest in animal models.
In mice, prolonged 2–3 day fasts triggered stem-cell-based regeneration (Cheng 2014). Early human data only — supervision territory.
Timeline synthesised from de Cabo & Mattson 2019 (NEJM) and Anton 2018 ("Flipping the Metabolic Switch", Obesity). Individual results vary.
Real screenshots, not mockups.
Start a protocol and the dashboard tracks elapsed time, the active metabolic phase, and the three numbers that matter — ketones, glucose, and your GK Ratio — updating as you log. No guessing where you are in the fast.
Pick the fast that fits — a one-day reset or a 21-day self-experiment — each with its evidence base, expected ketone range, and the safe ramp to get there. The app recommends one based on your experience.
Sardines, water, electrolytes, ketones, glucose, weight, waist — quick-log chips for everything. The GK Ratio and GKI recompute instantly so you can literally watch yourself cross into the autophagy zone.
The Education hub carries the autophagy, ketosis, omega-3 and cycle-aware research in plain language — every claim tied to a paper. Read How Autophagy Works, the GK Ratio explainer, or the anonymized 21-day case study.
Join structured group challenges, post your progress, and see a weekly leaderboard ranked by autophagy hours. Moderated, opt-in, and never required — your logs stay private on your device by default.
Sardines, water, coffee or tea. Start gentle, progress when you're ready.
One-day metabolic switch. Cross the 16-hour mark with food on board — the easiest first fast.
24 hoursA sustainable daily 17-hour window with sardines as the eating window. Lifestyle-friendly.
17 hours / dayThree days of sardines + water. Targets insulin resistance; GK Ratio typically drops hard by day 3.
72 hoursDeeper autophagy and ketosis. Protein + omega-3 spare lean mass through the longer fast.
120 hoursAn extended self-experiment for very experienced fasters. Requires bloodwork and DEXA before and after, and medical supervision. The app flags contraindications first.
21 daysThirty-five peer-reviewed references behind the app and this page. Filter by topic; every card links to Google Scholar. We cite mechanism and human evidence separately — and never claim fasting treats or cures any disease.
Straight answers. The app is a tracker and educational tool — not a doctor.
Eating a small amount of pure protein and fat keeps insulin low enough for autophagy to ramp up, and the absence of carbohydrate keeps you in fat-burning. In mechanistic terms you get much of what a water fast offers. In a strict religious or cultural sense — no, you are eating. The app is explicit about this.
Nutrient density (22–25 g protein, ~1–1.7 g long-chain omega-3, B12, selenium, calcium from the bones per can), a low toxin load (small fish don't bioaccumulate mercury like big species), and they're cheap and shelf-stable — practical for a multi-day protocol.
Far less than on a water fast. Protein turnover stays closer to maintenance because you're getting real protein each day, and omega-3 is anti-catabolic. You'll still lose some lean mass on extended fasts (>5 days), but much less than fasting on water alone.
For most healthy adults, short protocols (24–72h) are generally well tolerated; longer ones need medical supervision. The app's onboarding flags contraindications — pregnancy, eating-disorder history, diabetes or blood-pressure medication, very low BMI, heart or kidney conditions — and adjusts. It is not a substitute for your doctor.
Keto and carnivore are diets you sustain. A sardine fast is a structured, time-bound protocol with a defined start and end, designed to push you toward autophagy and then return you to normal eating. Many people do daily 17h IF between sardine challenges.
Yes — with cycle awareness. The app suggests avoiding extended fasts in the late luteal phase (roughly days 18–28) and concentrating deeper protocols in the follicular phase (roughly days 6–14). Onboarding asks about your cycle so the guidance fits.
The GK Ratio is glucose (mg/dL) ÷ ketones (mmol/L) — a practical readout of how deep you are in the fasted, low-insulin state; under ~80 is the target. The GKI (Glucose-Ketone Index) is glucose (mmol/L) ÷ ketones (mmol/L), from the Meidenbauer 2015 paper. You need a glucose and ketone meter to use them; the app works without one too.
On your phone. No account is required to track. Apple Health sync is optional. The app is local-first by design; the AI coach (Pro) processes your message in-memory and does not retain it.
Free to download. SardinesFasting Pro unlocks the AI coach, CGM/CKM sync, doctor-ready PDF reports and hour-by-hour autophagy tracking — €4.99/month or €49/year, cancel anytime.
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