Who Should Not Do Intermittent Fasting Without Advice?
Who should not do intermittent fasting without advice? Diabetes medicines, pregnancy and eating disorders need care; few data on children or over-60s.
- Written by
- Blimbi Editorial
- Reviewed by
- Blimbi editorial team
- Reading time
- 5 min
Editorial review against cited sources, not medical review. Educational, not medical advice.
In 30 seconds
Ask a clinician before fasting if you use insulin, sulfonylureas, SGLT-2 inhibitors or diuretics, have type 1 diabetes or a high A1C, or recently had a heart attack, stroke or fever. Pregnancy is not the time to diet, and an eating disorder calls for professional advice first. Evidence is thin for children and adults over 60.
- Insulin, sulfonylureas, type 1 diabetes and a high A1C call for a plan with your diabetes team before any fast.
- Do not stop or change prescribed medicines to try fasting without medical advice.
- NHS guidance says pregnancy is not the time to go on a diet.
- Eating very little and strict food routines can be signs of an eating disorder; see a GP if that sounds like you.
- Fasting trials mostly enrolled adults aged 60 or younger, so results don't necessarily apply to children or older adults.
Who needs advice before fasting?
The trials studied mostly healthy adults. The groups below have a specific reason to talk to a professional first, and for some the advice is not to fast.
An NIDDK diabetes specialist links insulin and sulfonylureas with low blood sugar during a fast, says type 1 diabetes carries more risk than type 2, and supports fasting with diabetes only under medical supervision.Source 1
He adds that SGLT-2 inhibitors and diuretics raise dehydration risk, strongly discourages fasting with an A1C of 9% or higher or a fever in the past week, and notes extra risk after a heart attack or stroke in the last three months.Source 1
Do not stop or change prescription medicines to attempt fasting without professional medical advice and an individual plan.Source 1
| Group | What the sources say |
|---|---|
| Insulin or sulfonylurea users | Main risk is low blood sugar; fast only with a plan from your diabetes team |
| Type 1 diabetes or an A1C of 9% or higher | More risk of low or high blood sugar and ketoacidosis; the NIDDK expert strongly discourages fasting with a high A1C |
| Heart attack or stroke in 3 months, or recent fever | Dehydration and a drop in blood pressure; no fasting with a fever in the past week |
| SGLT-2 inhibitors or diuretics | More fluid loss; review them with your clinician first |
| Pregnancy | NHS: pregnancy is not the time to go on a diet |
| Eating disorder, now or in the past | NHS: eating very little and strict food routines can be symptoms; see a GP |
| Children and adults over 60 | Trials mostly enrolled adults aged 60 or younger, so results don't necessarily apply |
Two groups outside diabetes have direct public guidance behind them.
NHS pregnancy guidance says pregnancy isn't the time to go on a diet, as it may harm the health of the unborn baby, and advises asking a midwife or GP about any concerns about weight.Source 2
NHS guidance lists eating very little and very strict food routines among eating-disorder symptoms, notes that teenagers and young adults are mostly affected, and advises seeing a GP as soon as possible.Source 3
What evidence covers these groups?
Mixed evidence
Expert and official guidance, not trials of these groups
No trial here tested fasting in these groups. The diabetes advice comes from an NIDDK interview with a diabetes specialist for health professionals; the pregnancy and eating-disorder points come from general NHS pages that do not mention fasting.Source 1Source 2Source 3
That leaves real gaps at both ends of life.
An NIA overview says there is not enough evidence to recommend any calorie-restriction or fasting diet, and that much more needs to be learned about effectiveness and safety, especially in older adults.Source 4
The same overview notes that trials have typically recruited adults aged 60 or younger, so results don't necessarily apply to children.Source 4
What should these groups do?
Talk to a qualified health professional before fasting if you are pregnant or breastfeeding, under 18, living with or recovering from an eating disorder, have diabetes, take insulin or a medicine affected by meal timing, are an older adult, or are acutely ill. Do not change the dose or timing of any medicine without your clinician. See Blimbi’s safety guide.
Frequently asked questions
Can I fast if I have diabetes?
Only with an individual plan from your diabetes team. With insulin or a sulfonylurea, fasting can cause low blood sugar, and cutting doses too far can push glucose too high.Source 1
Can I do intermittent fasting while pregnant?
NHS guidance says pregnancy isn't the time to go on a diet, as it may harm the health of the unborn baby. Talk to your midwife or GP about eating and weight during pregnancy instead of starting a fasting plan.Source 2
Sources
Fasting Safely with DiabetesMartin M. Grajower. National Institute of Diabetes and Digestive and Kidney Diseases, August 26, 2020.Official guidance
Weight gain in pregnancyNHS. NHS, July 6, 2022.Official guidance
Overview – Eating disordersNHS. NHS, January 23, 2024.Official guidance
Calorie restriction and fasting diets: What do we know?National Institute on Aging. National Institute on Aging, August 14, 2018.Official guidance
Low blood sugar (hypoglycaemia)NHS. NHS, August 3, 2023.Official guidance
DehydrationNHS. NHS, May 1, 2026.Official guidance