During a long fast, your body works quite hard to keep blood glucose (sugar) in a safe range, but what happens depends a lot on whether you are healthy or have diabetes / other illness.

1. In a healthy person (no diabetes)

Roughly:

• First 12–24 hours

- The liver slowly uses up its stored glycogen (stored glucose). - Blood sugar may fall slightly but usually stays in a normal or near‑normal range.

• After about 24 hours and onwards

- Liver and kidneys start making new glucose from protein and glycerol (this is called gluconeogenesis). ( ncbi.nlm.nih.gov) - The body shifts more and more to burning fat and producing ketones, which the brain can use for energy. ( en.wikipedia.org) - Because of this shift, blood glucose often settles a bit lower than usual (for many people around 70–85 mg/dL instead of 90–100 mg/dL), but usually does not crash in a healthy person. ( academic.oup.com)

So in a normal, healthy adult, even with several days of fasting, the body usually keeps blood glucose just low‑normal, while ketones go up and supply the brain.

2. When can blood glucose become dangerous?

• People with diabetes (especially on insulin or tablets like sulfonylureas)

- Very high risk of dangerous low sugar (hypoglycemia) during a fast if medicines are not adjusted. ( journals.ekb.eg) - Type 1 diabetes has an additional risk of ketoacidosis (DKA), which can be life‑threatening.

• Children, very thin or very elderly people, or those with liver/kidney disease

- Their body may not maintain glucose well; they can develop low sugar, weakness, confusion, fainting, even seizures.

If any of these apply, long fasting must not be done without a doctor’s direct guidance.

3. Jain dharm viewpoint

In Jainism, upvās / long fasts are a powerful tapas, but:

• Ārogyā (health) is also part of dharm.

Harming your own body ignorantly is not considered true tapas; it can even increase himsā (violence) towards this body.

• If someone has illness like diabetes, heart disease, pregnancy, old age weakness etc., Acharyas and upādhyāys usually advise:

- Shorter or modified fasts (e.g., ekāsan, bēsanu, limited upvās) - Or giving up long fasts altogether and focusing on other forms of tapas (swādhyāy, pratikraman, japa, etc.)

• If during fast you get dizziness, blacking out, confusion, chest pain, severe weakness, Jain dharm does not insist you continue stubbornly.

Breaking the fast carefully, on medical advice, is better than risking serious harm.

4. Practical guidance if you plan a long Jain fast

• If you have any medical condition (especially diabetes, BP, heart, kidney, liver issues, are elderly, or on regular medicines):

- Consult your doctor first and clearly say you want to do a Jain fast. - Ask exactly how to adjust medicines and how to monitor sugar.

• During the fast:

- If you feel very weak, confused, shaking, sweating, or about to faint, treat it as potentially low sugar and stop the fast safely and seek medical help.

• Remember: in Jainism, right wisdom (samyak jñān) and non‑violence (ahimsā) come before sheer length of fast.

If you tell me:

• Your age
• Whether you have diabetes or take any regular medicines
• How long you are thinking to fast

I can explain what is generally considered safer from a Jain‑dharm and basic health point of view (but final word must be from your doctor).