Who should be careful with fasting

Quick checklist

If any of these is you, do not start an unsupervised fast. Use this as a pocket list, not a clearance form.

• Pregnant or breastfeeding
• Under 18
• Underweight, or a clinician has said you need more food
• Current or past eating disorder, or food already carries shame or rigid rules
• Diabetes, especially if you use insulin or other drugs that can drop blood sugar
• Kidney disease, liver disease, gout, advanced heart disease, or a history of fainting, seizures, or adrenal disorders
• Recovering from surgery, an active infection, or cancer treatment
• Medicines that lower blood sugar or blood pressure, water pills (diuretics), some heart medicines, or lithium
• Unsure — ask your clinician. Do not start until they say it is appropriate.

Groups that generally should not fast unsupervised

Pregnancy and breastfeeding. Energy and nutrient needs are different. Recreational fasting is not a reasonable experiment then. If you menstruate and are not pregnant, that is a different question: read Fasting, periods, and hormones for more information.

Under 18. Growing bodies are not the same as adult wellness plans. This app is not for children.

Underweight, or anyone whose clinician has said they need more food, not less clock time.

Current or past eating disorders, including anorexia, bulimia, binge-eating disorder, and rigid restriction around “clean” eating. A fasting timer can become a tool for harm. If food already carries shame or rigid rules, do not add a clock. Get specialist care.

Conditions that raise the stakes

Diabetes (type 1 or type 2), especially if you use insulin or other drugs that can drop blood sugar. Fasting can cause dangerous lows. It can also change how those medicines are timed. That belongs in a clinic.

Kidney disease, liver disease, gout, advanced heart disease, or a history of fainting, seizures, or adrenal disorders. Fluid, minerals, and blood pressure all shift when you stop eating.

Recovery from surgery, an active infection, or a cancer treatment plan. Do not add a fast on top of medical care unless the team that knows you said so.

This list is not complete. Rare conditions exist. “I feel fine” is not a medical workup.

Medicines that change the question

Anything that lowers blood sugar or blood pressure can become too strong when you are not eating. Water pills (diuretics), some heart medicines, and lithium are other examples people should not adjust from a blog.

Do not skip or change a prescribed dose because a timer is running. Call the prescriber. Bring this list if it helps you remember what to ask.

Supplements are not automatically safe. Extra sodium, potassium, or magnesium can be harmful with the wrong kidneys or the wrong pills. Read Hydration and electrolytes for more information.

What this app will not do

It will not tell you that fasting is appropriate. The notice you agree to on first use is a notice, not a screening visit.

It will not stop you when you should stop. You have to tap End Fast. See When to stop a fast. Keep that closer than any name on the timer.

It will not replace emergency care. Confusion, fainting, chest pain, severe weakness, or a sense that something is badly wrong means stop, eat if you can do so safely, and get help.

If this list is not you

If none of the groups, conditions, or medicines above apply, you still need a plan you can live with, not a dare. How to start fasting is day one of a daily window. Choosing a starting window is how to pick the hours.

If you already mean more than a day, that is extra caution, not extra clearance. Start with Before a longer fast.

The online fasting timer will count hours. It still cannot see your labs. The legal and health disclaimer is the same limit in legal language.