Read this before you start.

Hard exclusions — do not attempt this protocol

These conditions make a sardine fast actively unsafe. The list is not exhaustive; it covers the most common and most serious contraindications. If any apply, this protocol is not for you.

• Type 1 diabetes (insulin-dependent) — Fasting can be life-threatening without medical supervision and insulin protocol adjustment.
• Type 2 diabetes on insulin or sulfonylureas — Same risk class as T1D; only attempt under endocrinologist supervision.
• History of any eating disorder (anorexia, bulimia, BED, OSFED) — Restrictive protocols can trigger relapse.
• Pregnancy or breastfeeding — Fasting is contraindicated; nutritional needs are elevated.
• Underweight (BMI < 18.5) — Calorie restriction is medically inappropriate.
• Children and adolescents under 18 — Energy needs and developmental considerations.
• Active cancer treatment without explicit oncologist sign-off — Interactions with chemotherapy, surgical recovery, and altered nutritional needs.
• Chronic kidney disease (Stage 3 or higher) — High-protein, high-purine intake risks.
• Severe hepatic disease — Protein metabolism risks.
• Bariatric surgery patients — Radically altered nutrient absorption.
• Active eating disorder symptoms — Restriction, binge cycles, body-image distress.
• Mercury sensitivity, fish allergy, or shellfish cross-reactivity — The protocol is built around a single ingredient; allergies make it inappropriate.
• Adrenal insufficiency without endocrinologist supervision — Cortisol regulation considerations.

Soft exclusions — proceed only with medical supervision

These conditions don’t automatically rule out a sardine fast, but they raise the risk profile enough that you should clear the protocol with a clinician who knows your case before starting.

• Hypoglycemia history
• Gout or hyperuricemia (sardines are high in purines — manageable with adequate hydration but consult)
• Histamine intolerance (canned fish is histamine-rich)
• Cardiovascular disease, especially atrial fibrillation
• Currently taking: warfarin / coumadin (vitamin K + omega-3 interactions), antihypertensives (BP often drops on a fast), antipsychotics, lithium, diuretics, MAOIs (tyramine in aged fish)
• Pre-existing electrolyte abnormalities
• Recent surgery or hospitalization
• Significant alcohol consumption (within 7 days of starting)
• Active GI disease (IBD flare, gastroparesis, severe GERD)
• Mental health crisis or active depression
• Endurance athletes mid-training block (energy availability concerns)
• Female athletes with history of amenorrhea / RED-S
• Postmenopausal women on HRT — metabolic interactions

Universal recommendation: consult your doctor before starting a fast, regardless of whether any exclusion applies to you. The list above is a floor, not a ceiling.

When to STOP the fast immediately

Stop a sardine fast and seek medical attention if you experience any of the following. This list is pinned in every cohort thread and at the top of every protocol page on purpose.

• Fainting or near-fainting
• Heart palpitations, irregular heartbeat, or chest pain
• Prolonged confusion, disorientation, or difficulty speaking
• Severe weakness that prevents normal activity
• Severe muscle cramps that don’t resolve with electrolytes
• Vomiting that prevents fluid intake
• Any symptom of dehydration (dark urine for >12 hours, dizziness, dry mouth)
• Mental health crisis: severe depression, suicidal ideation, panic attacks
• Any symptom that worries you — listen to your body

It’s normal to feel hungry, mildly tired, or slightly headachey. It is not normal to feel any of the above. Stop, eat, and reassess.