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Common
Red flags
6
This article is educational and does not replace your doctor's advice. Seek urgent care for any red-flag symptoms.
What is it?
Intermittent fasting means alternating periods of eating with periods of little or no calorie intake. Common forms are: time-restricted eating (eating within a set window, for example 8 to 10 hours, and fasting for the rest, such as the 16:8 pattern); alternate-day fasting (a very low-calorie day, about 500 kcal, alternating with normal days); and the 5:2 pattern (two low-calorie days a week). Ramadan fasting is a religious obligation, not a diet: it is a month of dawn-to-sunset abstinence from food and drink, so it is a form of time-restricted eating with no fluids during the day. It differs from diet fasting in that fluids are also avoided, the eating window is at night, and the pattern is social and spiritual.
How common is it?
Intermittent fasting is one of the most popular diet trends. Ramadan fasting is practised every year by hundreds of millions of Muslims, including most adults in Saudi Arabia, and many people with long-term medical conditions also choose to fast, which makes advice before Ramadan important.
Why does it happen?
Fasting may help weight by reducing the number of occasions and hours in which a person eats, which lowers calories for many people. Effects on body clock, insulin levels and fat burning are being studied. During Ramadan, weight changes depend on what is eaten: heavy, sugary, fried iftar meals and late-night sweets can cancel the calorie savings of the day, and less sleep and less activity can add to weight gain. Dehydration, reduced medicine absorption timing and changes in sleep can also affect health.
Symptoms
- Hunger, headache, irritability and trouble concentrating, especially in the first days
- Constipation, heartburn and reflux after large meals at iftar or suhoor
- Tiredness, sleep disruption and daytime sleepiness
- Dizziness or fatigue from dehydration, especially in hot weather
- Weight gain, bloating and high blood sugar after sugary or fried iftar foods
Red flags — seek urgent medical care
Shaking, sweating, confusion, palpitations, or blurred vision during the fast (diabetes)
Low blood sugar can be dangerous. Break the fast immediately and treat it. You are permitted to break the fast in illness. Call your doctor.
Blood sugar above about 16.7 mmol/L (300 mg/dL), or thirst with frequent urination, nausea, vomiting and abdominal pain
Possible dangerously high blood sugar or ketoacidosis. Break the fast and go to the emergency room.
Fainting, severe dizziness, very dark or little urine, or confusion
Severe dehydration. Break the fast, drink fluids and seek care.
Vomiting blood, black stools, or severe upper abdominal pain
Possible ulcer bleeding or other emergency. Break the fast and go to the emergency room.
Pregnant: reduced baby movements, dizziness, fainting or contractions while fasting
Break the fast and contact your maternity unit or go to hospital the same day.
Confusion, drowsiness, swelling, vomiting blood or black stools in cirrhosis
Emergency; do not continue to fast. Go to hospital.
How is it diagnosed?
There is no test for choosing intermittent fasting, but a pre-fasting assessment is strongly advised for anyone with a medical condition. IDF-DAR (International Diabetes Federation and Diabetes and Ramadan Alliance) guidelines recommend a risk assessment 6 to 8 weeks before Ramadan for people with diabetes, with a review of blood sugar, medicines, kidney function, blood pressure and complications, and structured education. For other conditions (cirrhosis, kidney disease, heart disease, ulcers, inflammatory bowel disease, pregnancy), your own doctor judges the risk. Doctors also ask about past or current eating disorders, because fasting can trigger relapse.
What the latest science says
Intermittent fasting for weight: randomised trials and systematic reviews show that, compared with doing nothing, intermittent fasting produces modest weight loss, but compared with continuous daily calorie restriction the difference is small or none. In a 12-month randomised trial of alternate-day fasting versus daily restriction (JAMA Internal Medicine 2017) weight loss was similar and dropout was higher with fasting. A trial of 16:8 time-restricted eating without calorie counting (JAMA Internal Medicine 2020) found no significant extra weight loss versus usual meals, with some lean-mass loss. A 12-month trial in China (NEJM 2022) found that adding an 8-hour eating window to calorie restriction gave no significant extra benefit. Systematic reviews rate the certainty as low to moderate and long-term data as scarce. A conference abstract in 2024 reported a possible association between very short eating windows and cardiovascular death; this was observational, not peer-reviewed at the time and cannot prove harm, but it shows long-term safety is not established. Ramadan fasting: systematic reviews of healthy adults report an average weight loss of roughly 1 to 1.5 kg during the month, most of which returns within weeks after Ramadan; some people gain weight. The IDF-DAR practical guidelines (2021) classify people with diabetes into very high, high and moderate/low risk groups; people at very high risk (for example type 1 diabetes with recent severe hypoglycaemia or ketoacidosis, poorly controlled diabetes, pregnancy with diabetes, advanced kidney disease, acute illness) are advised not to fast. For patients with cirrhosis, fasting is not recommended in decompensated disease (ascites, bleeding, encephalopathy), and stable compensated patients should be individually assessed.
Outlook — what to expect
For healthy adults, a moderate form of intermittent fasting or Ramadan fasting is generally safe, and may suit people who find a defined eating window easier than counting calories. It is not magic: results depend on total food quality and quantity. For people with medical conditions, the outlook depends on a careful risk assessment, treatment adjustment and monitoring; many can fast safely with their doctor’s guidance, while for some the safest choice is not to fast, which is permitted by religion.
Treatment
Habits & Lifestyle
Good habits make fasting safer and protect your weight.
- See your doctor 6 to 8 weeks before Ramadan if you have diabetes, heart, kidney, liver or gut disease, or take regular medicines.
- Sleep enough: keep a regular sleep pattern, with a short nap if possible.
- Stay active: gentle walking after iftar (and light strength exercise) helps maintain muscle and weight.
- Avoid strenuous activity and heat exposure in daytime; rest in the shade or indoors.
- If you break the fast for health reasons, do not feel guilt; follow your doctor’s advice and make up days later or as your scholar advises.
- After Ramadan, return gradually to your usual routine and keep the healthy habits.
Diet
What you eat in the eating window matters more than the fast itself. See also our Ramadan and GI conditions article.
- Break the fast gently with water, one to three dates, and a light soup or salad, then pray, and then eat a balanced main meal. Avoid eating very large amounts quickly.
- Fill half the main-meal plate with vegetables and salad, a quarter with protein (fish, chicken, lean meat, eggs, legumes) and a quarter with whole grains or starch.
- Limit fried foods (samboosa, fried pastries), sugary drinks, juices, and syrup-soaked sweets (kunafa, qatayef, luqaimat). Choose fruit, laban or yoghurt with a small portion of sweets once in a while.
- Take suhoor and do not skip it: choose slow-digesting foods (oats, whole-grain bread, eggs, ful, yoghurt, nuts, vegetables) and avoid very salty or sugary foods that increase thirst.
- Drink at least 8 glasses of water or unsweetened fluids between iftar and suhoor, spread out; limit caffeine as it increases fluid loss.
- For weight loss in Ramadan: keep portions moderate, avoid grazing after the main meal, and aim for steady loss rather than a quick drop. Rapid loss is not encouraged.
- For non-religious intermittent fasting: choose a window you can keep (for example 10 to 12 hours of eating), drink water, tea or coffee without sugar during the fast, and eat balanced meals in the window. It is not a licence for unlimited food in the window.
Medications
Medicines often need a new schedule during fasting. Never change doses on your own; agree a plan with your doctor or pharmacist before fasting begins.
- Diabetes medicines: insulin and sulfonylureas carry the highest risk of low sugar and usually need dose and timing changes; some other tablets may be taken at iftar and suhoor. Check your blood sugar as often as advised, including during the fast; checking blood sugar does not break the fast.
- Medicines for blood pressure, reflux, ulcers, bowel disease and others may be rescheduled to the eating hours; some can be switched to once-daily forms.
- Do not stop essential medicines (for example steroids, immunosuppressants, anticoagulants, antiepileptic or heart drugs) without medical advice.
- Anti-obesity medicines (GLP-1) can cause nausea and reduced drinking; discuss with your prescriber before fasting.
- Avoid herbal and slimming products during fasting.
Procedures & Surgery
There is no procedure for fasting itself, but some procedures and tests need planning around it.
- Blood tests that need fasting (cholesterol, glucose) are best scheduled in the morning outside Ramadan or at iftar-timed visits, as advised by your clinic.
- Endoscopy or colonoscopy with sedation may need a rescheduled time; discuss timing with your endoscopy unit.
- Bariatric surgery patients should review fasting with their surgical team, because of risks of dehydration and low intake.
Living with the condition
- Prepare early: shop, plan balanced iftar and suhoor menus, and agree your medicine plan before the month begins.
- Know your personal stop-fasting rules and tell your family.
- Keep a small record of weight and blood sugar during the month, and share it at your follow-up visit.
- If you use fasting for weight control, watch for obsession with food or weight; seek help if fasting is driving binge eating.
In the Saudi context
Ramadan is a time when many Saudis gain rather than lose weight because of rich iftar buffets, late-night sweets and less activity. Plan simple iftar meals, share large dishes rather than preparing too much, and walk after taraweeh or iftar. Medical rulings in Islam exempt the sick, the pregnant and breastfeeding women who fear for themselves or their baby, travellers and others; a doctor’s advice that fasting would harm you is a valid basis to not fast, and you can make up the days or give fidya according to your scholar’s guidance. Many hospitals and diabetes centres in the Kingdom run pre-Ramadan clinics and education sessions; ask for one. For people with gut or liver conditions, see our article on Ramadan and GI conditions. In hot months, outdoor workers need particular care for dehydration.
Questions to ask your doctor
Save this list or print it before your appointment — doctors appreciate prepared patients.
- Is it safe for me to fast, given my conditions and medicines?
- How should my medicines be timed or changed during fasting?
- When should I break my fast for health reasons?
- Is intermittent fasting a good option for my weight goals compared with a normal diet?
- Can I get a pre-Ramadan review and education session?
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Status: Approved for publication by SGA; individual clinician review is ongoing · Published 24/04/2026
For general education only; it does not replace your doctor’s advice. Individual clinician review of this guide is ongoing. SGA clinician? Review this guide