The Contraindication List
Every fasting page on this site assumes you are not on this list. This page is where the list lives, row by row, with no grading and no exceptions: pregnancy, eating-disorder history, underweight, insulin-treated diabetes, and medications that depend on food or stable electrolytes. One match anywhere means no fasting protocols — not shorter, not supervised, not "just on weekends." The people who clear or evaluate each row are named here, because that is who the decision belongs to.
What the evidence supports
- Hunger and restriction patterns are documented relapse triggers for people with eating-disorder history — restriction protocols are contraindicated, period.
- Fasted hours are hypoglycemic hours for insulin users; insulin dosing and food timing are tightly coupled by design.
- Guidelines documenting refeeding risk name the same profiles this list protects: very low BMI, significant unintended weight loss, and prolonged minimal intake (NICE CG32, 2006).
What remains uncertain
- How short a "fast" must be before it stops mattering in pregnancy — the safe answer is that fasting protocols are simply not studied here, so none are recommended.
- Whether a clinician-managed trial could ever fit someone with an eating-disorder history — a question for their treatment team, not for this page or any website.
- The exact thresholds where individual medications become risky — they vary by drug, dose, and person, which is precisely why prescribers decide.
Evidence last reviewed: August 21, 2026. Conclusions may change as new research is published.
the pre-screen list
How to Read This List
- 🚪 One match, anywhere, is the answer — this is not a scorecard where mild matches cancel out. The safety chapter that owns this series' rules puts it as a wall, not a suggestion; this page walks the wall row by row.
- 📅 The list is not seasonal — it applies to every fast and every season of life. A person cleared at twenty-five can be on this list at thirty-five without any fault — pregnancy, a new medication, a new diagnosis, or weight that drifted down change the answer.
- 🩺 Nobody on this page clears you — the rows below name who holds each decision: the OB or midwife, the clinician managing the eating-disorder history, the prescriber, the diabetes team. When a row applies, the conversation replaces the protocol.
The Hard-No Rows
| Group | Why it's a hard no | The rule |
|---|---|---|
| 🤰 Pregnant or breastfeeding | Nutrient demand is continuous; fetal growth and milk supply pay the bill | Never — no fasting beyond overnight sleep |
| ⚖️ Underweight (BMI under 18.5) or losing weight without trying | No reserves to spend; fasting accelerates the loss | Never — eat normally; weight first |
| 🧠 Eating-disorder history, active or past | Restriction patterns are the relapse trigger — fasting is a restriction pattern | Never — no fasting protocols, this site's position |
| 💉 Type-1 diabetes on insulin (or sulfonylureas) | Fasted hours become hypoglycemic hours; dosing is tied to food by design | Never — only with the diabetes team, and this page does not write that plan |
| 💊 Medications that need food or stable electrolytes (lithium, digoxin, diuretics, some blood-pressure drugs) | Absorption and blood levels shift on an empty stomach | Never — keep the meal schedule unless the prescriber says otherwise |
| 🧒 Children and teenagers | Growth and brain development need steady energy | Never — not the audience for any protocol here |
Every row is "never" deliberately — graded lists invite negotiation, and these profiles do not need it.
Why the List Is a Wall
- 🤰 Pregnancy is continuous demand — there is no safe "catching up" meal after a fasted day; growth and placental function run on a schedule fasting cannot negotiate with. The OB or midwife owns the answer, and the default is no.
- 🧠 Eating-disorder history is the row where people often argue hardest — "it's different now," "just time-restricted," "I'm in control this time." The pattern is documented and the stakes are high; the conversation belongs with a clinician who knows the history, and no fasting protocol is the honest recommendation this site can make. If disordered eating is present or returning — even without a formal diagnosis — that is the row that applies, treatment support first.
- ⚖️ Underweight is a reserves problem — a BMI under 18.5, or weight that falls without trying, means there is no buffer; the body spends muscle and function before anyone notices. The prolonged-fasts topic carries the same line at its boundary: refeeding risk rises in exactly these profiles, and the guidelines name them (NICE CG32, 2006).
- 💉 Insulin is the hardest strict row — for type-1 diabetes, insulin doses are calibrated to meals, and skipped meals mean the insulin that remains works on an empty tank. The schematic below shows the shape of the problem; the diabetes team owns the plan, and this page will not sketch one.
Medications: The Unseen Row
The medication row is the one people forget they are on. Daily pills are background noise until an empty stomach changes what they do — lithium and electrolyte levels shift with food and hydration, digoxin has a narrow window, diuretics empty the minerals fasting depletes, and some blood-pressure drugs combine with fasting to produce dizziness and fainting. The what-breaks-a-fast topic covers the intake ledger; the medication side is simpler: if a drug needs food, stable electrolytes, or timing, the prescriber and pharmacist decide whether a fast fits — and most of the time the answer is no, and the fast is the thing that moves.
- 💊 The question to ask — "Does any medication I take depend on food timing, blood levels, or electrolytes?" The answer is usually in the pharmacy leaflet or one call to the pharmacist; the call costs ten minutes and buys the whole decision.
- 📉 The blood-pressure case — fasting lowers intake, and some pressure drugs lower it further; lightheadedness on standing is the early warning. Anyone on pressure medication who fasts should have the prescriber in the loop before, not during, a fainting episode.
- 🚩 The honesty test — if you would hide the fast from the person who prescribes your medication, that is your answer. The prescriber's office is where the plan gets built; nothing here overrides a medication that needs food.
⚠️ One match, anywhere
The rule this page refuses to soften: one match on the list and the answer is "no," not "less." Shorter windows, "clean" fasts, and supervised versions do not clear a hard contraindication — they negotiate with one. The clinicians named in each row — the OB or midwife, the clinician who knows the eating-disorder history, the registered dietitian, the prescriber, the diabetes team — are the people who hold these decisions, and every one of them costs less than a symptom you decided to tough out.
The Re-Screen Habit
- 📅 Every season, not once — run the list at the start of each fasting block, because life changes the rows: a positive pregnancy test, a new prescription, a diagnosis, weight drifting down, disordered patterns returning.
- ⚖️ The scale tells the truth — losing weight without trying is its own red flag and moves anyone into the underweight row regardless of starting point. Unintended loss means evaluation, not a longer fast.
- 🧠 The ED row is the hardest to check honestly — it is the row a person can talk themselves out of. If food thoughts are taking up more space, if restriction feels like control, if the fast feels like the point rather than the schedule — that is the row applying, and support belongs with a clinician who knows eating disorders, not with a stricter window. The craving-defense playbook later in this series defers the same way.
- 🚩 Symptoms always stop — fainting, chest pain, palpitations, confusion, or vomiting mid-fast are medical events, not protocol problems; stop the fast and seek care. No list on this page excuses a trip to urgent care.
The Refeeding Boundary
This list protects the front door; the refeeding side belongs to the refeeding protocol in this series, and the two connect at one point: the people here are substantially the same profiles the guidelines name as refeeding-risk — very low BMI, significant unintended weight loss, and prolonged minimal intake (NICE CG32, 2006; the BMJ review of refeeding syndrome makes the same list, Mehanna 2008). The overlap is not coincidence: the bodies that should not fast hard are the bodies that pay most when intake restarts wrong, so the two pages act as one system.
Questions, Answered Briefly
- ❓ Does a past eating disorder ever clear? — That is a question for the clinician who knows the history, and the honest default is that fasting remains off the table for good. Treatment and support belong to the team; a fasting schedule is not part of this site's advice in this row.
- ❓ I'm pregnant — is a 12-hour overnight gap okay? — Overnight sleep is not a fasting protocol, and nighttime fasting is not what this list means. Anything beyond ordinary overnight sleep is the no; the OB or midwife decides, and schedules wait until after breastfeeding ends.
- ❓ My clinician said fasting is fine for me — does that beat this list? — If a row applies and the clinician who knows the condition says it is safe, their plan replaces this page — this page does not diagnose, clear, or override. What it asks is that the conversation actually happened with the person who holds the medical record.
- ❓ I take metformin — am I on the list? — Not by default; metformin is not the insulin row. But the prescriber decides: any drug that can cause low blood sugar, needs food, or touches electrolytes moves the answer toward no. One call settles it.
- ❓ What if I'm on the list but "only want to try" 14 hours? — The list does not have a trial-size section. Pregnancy, relapse risk, hypoglycemia, and medication levels do not scale down with the window; the row applies at 14 hours as much as at 72, and the named clinician is who you argue with — not a schedule.
The Bottom Line
- Six rows, every one a "never" — pregnancy, underweight, eating-disorder history, insulin-treated diabetes, food-dependent medications, childhood.
- The list is a wall, not a scorecard — one match anywhere answers the question, with no grading and no trial sizes.
- Clinicians hold each row by name — OB, prescriber, diabetes team, registered dietitian, ED-informed clinician; the conversation replaces the protocol.
- Re-screen every season — pregnancy, new medications, weight drift, and returning disordered patterns move people onto the list without notice.
Related Topics
- National Institute for Health and Care Excellence, "Nutrition support in adults," Clinical Guideline CG32 (2006)
- Mehanna et al., "Refeeding syndrome: what it is, and how to prevent and treat it," BMJ (2008)
- American Psychiatric Association, Diagnostic and Statistical Manual of Mental Disorders, 5th ed. (2013)
- Wilhelmi de Toledo et al., "Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects," PLOS ONE (2019)