Ramadan Fasting: What Happens in Your Body and How to Get Through Your Fasting Days Well

Tuesday, just after half past three. Maybe you know this moment.

If you know this scene, you are in good company. In a survey from 14 countries, headaches during Ramadan fasting occurred mainly in the afternoon and in the time before iftar. That is not a sign of weakness. It is a body handling three changes at once: less energy, no water and a shifted night.

One word up front: I am writing here as a physician. Whether, how and why you fast is your decision and not the subject of this article. My concern is physiology. What happens inside you, what do studies show, and where is a medical perspective worthwhile?

What sets Ramadan fasting apart from intermittent fasting?

In short: With intermittent fasting, you can drink during the fasting period. During Ramadan, you also go without water between dawn and sunset. On top of that, meals and part of your sleep move into the night. So your body faces three changes at the same time.

Maybe you have read about intermittent fasting and thought: I know this, just stricter. Even so, many of the tips do not fit. Drink plenty of water during the fasting period? Not possible. Eat your last meal at 6 pm? That is when your eating day is just getting started.

The difference is bigger than it sounds. An international expert group on diabetes and Ramadan states this explicitly in its recommendations: unlike most forms of intermittent fasting, Ramadan fasting also excludes water and other drinks.

Because Ramadan follows the lunar calendar, it moves through all the seasons in a cycle of about 33 years. In Germany, that makes a big difference. When it falls in summer, fasting days here can last longer than 16 hours. The international IDF-DAR guidelines count fasting days this long as an additional risk factor in diabetes.

Imagine three sliders on a mixing board: energy, fluids and rhythm. With intermittent fasting, you mainly move the first slider. During Ramadan, you move all three at the same time. That is why a fasting day feels different from a long morning without breakfast.

So take tips on intermittent fasting as inspiration, not as a plan. For Ramadan, three questions count: how do you get enough fluid at night? How do you protect your sleep? And do your medications fit the new mealtimes?

And now you know why advice on intermittent fasting only half fits Ramadan.

What happens in your body during a fasting day?

In short: After suhoor, your body first draws on the sugar stores in your liver, and later increasingly on fat. Your kidneys save water as well as they can. In the afternoon, mild dehydration, missing coffee and short sleep add up. That is exactly when many people get head pressure and trouble concentrating.

Remember the scene from the beginning? The pressure behind your forehead did not come at ten in the morning. It came in the afternoon. That is no coincidence.

Think of suhoor as filling the tank one last time before a long drive. After that, your body runs on reserves: first on sugar from the liver, later increasingly on fat. Only water cannot be topped up along the way. That is why your kidneys save wherever they can, and your urine gets darker.

An experiment from the US shows how little it takes.

For many people, there is also the coffee they are missing.

An older study from Riyadh painted a similar picture. On the first day of Ramadan, 41 percent of the hospital staff there who were fasting had headaches, but only 8 percent of those who were not fasting. The researchers named caffeine withdrawal as the most important external factor.

The international survey from 14 countries shows when the pressure builds most often: in the afternoon and before iftar. For 54.6 percent, the headaches improved after iftar. The association was strongest in people who already have migraine or other headache disorders.

And blood sugar? In healthy people, the liver usually keeps it within the normal range, even after many hours. You can read more about this in the next section. With diabetes and certain medications, things look different, and that is covered further below.

For the afternoon itself: feel free to move, but avoid heat and heavy physical work. Stand up slowly if you feel dizzy. And if you are confused, shaking, sweating heavily or feel close to fainting, this is not a moment to push through. From a medical point of view, that is the time to break the fast and drink.

And now you know why, for many people, the afternoon is the hardest part of the day during Ramadan.

What do studies show about weight, blood lipids, blood sugar and blood pressure?

In short: In healthy adults, meta-analyses show on average a little over one kilogram less body weight, slightly more favorable blood lipids, a minimally lower fasting blood sugar and a systolic blood pressure about 3 mmHg lower. Most effects are small and gone again after a few weeks.

At the end of Ramadan, many people step on the scale and are surprised. Some have lost weight, some have gained, and some see hardly any difference. All three experiences are common, and all three can be explained.

An earlier meta-analysis from Kerman in Iran, based on 35 studies, arrived at an average of 1.24 kilograms less at the end of Ramadan. In men it was 1.51 kilograms, in women 0.92. Here too, most of it was back after a few weeks.

The changes in blood lipids and blood sugar are similarly small. An analysis of 91 studies with 4,431 healthy adults found slightly lower LDL cholesterol and slightly higher HDL cholesterol. The authors speak of a possible temporary protective effect in the short term. Another meta-analysis of 72 studies with 3,134 healthy people found a minimally lower fasting blood sugar. Insulin, insulin resistance, leptin and adiponectin, on the other hand, did not change measurably.

If you want to use Ramadan as a nudge, choose a single habit for afterward. For example, the walk after dinner, the water bottle on your desk at work or a breakfast rich in protein and fiber that reminds you of a good suhoor.

And now you know why, for your metabolic values, Ramadan is more of a window than a result.

Why sleep and caffeine matter so much during Ramadan

In short: During Ramadan, people sleep less on average, 6.4 instead of 7.2 hours per night in one meta-analysis. The internal clock shifts along with mealtimes. On top of that, many people go through caffeine withdrawal during the day. Together, this can explain the tiredness in the afternoon.

The alarm goes off in the middle of the night. You eat, drink and lie down again. Two hours later, it goes off again. After two weeks, your sleep feels as if it has been cut into pieces.

Then there is the rhythm. Your internal clock is like an orchestra with a conductor in your brain. Light sets the beat, and meals and sleep tune the individual instruments. During Ramadan, some instruments suddenly play to a different beat than the light outside.

Caffeine plays a double role here. During the day it is missing, and that can trigger headaches. In the evening and at suhoor there is often plenty of it, and then it can disturb sleep that is already in short supply.

What you can do with this: cut back on coffee, black tea and energy drinks step by step in the weeks before Ramadan, as the researchers from Riyadh suggest. Protect a consistent block of sleep before suhoor, and keep the room dark if you lie down again afterward. And if your daily life allows it, allow yourself a short nap. You can read more about light and your internal clock in the article on chronobiology and morning light.

And now you know why your sleep plan during Ramadan deserves just as much attention as your meal plan.

How do I plan suhoor and iftar using blood sugar and electrolyte logic?

In short: Slow energy from fiber, protein, a little fat and foods rich in water suits suhoor. It is best to start iftar gently, with water and a small portion, and then to eat vegetables and protein before the carbohydrates. Spread your drinking over the evening and night instead of having it all at once.

For many people, iftar is the most beautiful moment of the day. The table is full, the family is there, and after a long day everything tastes twice as good. An hour later, you are lying heavily on the couch, wondering why you are so tired.

The blood sugar logic: slow energy in the morning, a gentle start in the evening

Think of carbohydrates as firewood. Sugar, juices and white flour are like newspaper: they flare up quickly and burn out quickly. Whole grains, oats and legumes are like thick logs. They burn slowly and give off warmth for a long time. Protein, fat and fiber can slow the fire down even more.

The international IDF-DAR guidelines on diabetes and Ramadan describe a meal plan that can be good guidance even without diabetes. It spreads energy across suhoor and iftar and relies on carbohydrates with a low glycemic index and plenty of fiber, on lots of vegetables and fruit, and on little fried food and few sweets. The recommendations based on the principles of the American and European diabetes associations additionally emphasize portion size and movement after meals.

Many people traditionally begin iftar with dates. The international recommendations for people with diabetes consider two to three dates for breaking the fast acceptable, because dates in small amounts have a low glycemic index. Here, the amount makes the difference.

The electrolyte logic: water needs an anchor

Salt is like an anchor for your water. A little of it holds fluid in the body. Too much of it draws water out of the cells and signals thirst. That is why the rule during Ramadan is not to avoid salt, but to be mindful of it.

A yogurt drink such as ayran or laban was not tested in this study. But it brings similar building blocks: water, protein and a little salt. Soup, cucumber, melon, tomatoes and yogurt count too, because they deliver water and minerals such as potassium in one package. Very salty foods at suhoor, on the other hand, such as heavily salted cheese, sausage or salty snacks, can increase thirst during the day ahead.

The principle behind it: when you drink a large amount all at once, a good part of it ends up in your bladder quickly. Smaller amounts, spread over the hours and taken with meals, seem to be retained better. How much you need in total depends on your body size, the heat and how active you are. If you have heart or kidney disease, the amount you drink should be agreed with your doctor.

Try it for one week: iftar in two stages, a water bottle in plain sight on the table until bedtime, and a suhoor that resembles a good breakfast more than a late dinner. After eating, a short walk can flatten the rise in blood sugar. You can read more about that in the article on movement after meals. How to ease back into eating gently after longer periods of fasting is covered in Breaking a fast well.

And now you know why, during Ramadan, it is not only what is on your plate that counts, but also when and in which order.

What happens to my medications during Ramadan?

In short: If you take medications in the morning, at midday and in the evening, during Ramadan you have to fit them into two time points. That can change how well they work and how well you tolerate them. Many people adjust their intake without consulting a doctor. A safer option is a conversation with your doctor a few weeks before Ramadan begins.

The pill organizer with its little compartments for morning, midday, evening and night. During Ramadan, it suddenly no longer fits your day. The obvious idea: just take everything at iftar. This is exactly where it is worth pausing for a moment.

Why is this tricky? Imagine the level of a drug in your blood as the water level in a bathtub. If you take all your daily doses at once, it overflows in the evening and is almost empty by the next afternoon. Some medications handle that well. With others, too little and too much lie close together, and experts then speak of a narrow therapeutic range.

The Aberdeen review also names poorer medication adherence as a typical downside of Ramadan. The problem becomes especially clear with medications that themselves move water or salt out of the body.

The international diabetes recommendations advise particular caution with these medications if someone is older, has reduced kidney function or low blood pressure, or also takes water pills. With insulin and sulfonylureas, on the other hand, the main concern is low blood sugar.

Sometimes there are preparations that are taken only once a day, or forms with delayed release. Whether switching is an option for you is up to your doctor, ideally with some lead time. For people with diabetes, the experts recommend ideally starting the consultation six to eight weeks before Ramadan begins. For other regular medications, I consider a similar lead time sensible.

Whether injections, sprays, drops or patches affect the fast is a religious question that I do not assess here. Medically, it can make sense to raise such alternatives openly.

And now you know why the most important appointment before Ramadan is often not on the family calendar, but with your doctor.

Ramadan fasting with diabetes: what do the guidelines say?

In short: The IDF-DAR guidelines sort people with diabetes into risk groups before Ramadan. Low blood sugar episodes are more common during Ramadan, especially with insulin and sulfonylureas. In a randomized trial, education before Ramadan combined with adjusted treatment clearly reduced severe hypoglycemia.

Maybe you have diabetes and have fasted anyway in recent years. Maybe it went well. And maybe there was that one afternoon when your hands suddenly started shaking and you did not know whether to keep going.

You can find the basics of fasting with type 2 diabetes outside of Ramadan in the article on fasting with type 2 diabetes. Here, the focus is on what makes Ramadan special: many hours without water, two meals at night and medications that have to fit around them.

In a later survey of 1,759 people with diabetes from several countries, 16.8 percent reported low blood sugar during Ramadan. Only 67 percent of them then broke their fast. So a third kept fasting despite low blood sugar.

That is why the 2021 IDF-DAR guidelines, backed by the International Diabetes Federation and the Diabetes and Ramadan International Alliance, rely on an assessment before Ramadan. A points score takes into account, among other things, the type of diabetes, previous low blood sugar episodes, treatment, kidney function, pregnancy, frailty, physical work and the length of the fasting days. This results in a low, moderate or high risk.

Simplified from the 2020 international recommendations for type 2 diabetes. There, very high risk also includes an average blood sugar above 300 mg/dL, an HbA1c above 10 percent and advanced dementia. The exact classification belongs in a medical consultation.

For people with type 1 diabetes, for children with type 1 diabetes and for pregnant women with diabetes or gestational diabetes, the recommendations generally advise against fasting. The IDF-DAR guidelines themselves mention that people with serious illnesses, including some with diabetes, may be exempt from fasting.

Have your risk assessed before Ramadan, ideally six to eight weeks ahead. Clarify which medications will be adjusted and when you should measure. And save the thresholds for breaking the fast somewhere visible on your phone.

And now you know why, with diabetes, preparation decides whether and how fasting is an option for you.

Who should be especially careful during Ramadan?

In short: People who should be especially careful include those who are pregnant or breastfeeding, people with diabetes, kidney disease or heart disease, older people, people with migraine or gout, and anyone taking several medications. For them, a medical assessment belongs before the first day of fasting.

In many families, almost everyone fasts during Ramadan. The grandmother, the pregnant sister, the uncle with his heart pills. Nobody wants to be the first to say: I cannot manage this right now.

If you nod at any of these points, that is not a no to Ramadan. It is a yes to a conversation with your doctor before the first day of fasting.

And now you know why a conversation with your doctor before Ramadan is not a sign of mistrust, but of care.

How does KPNI view Ramadan fasting?

Clinical Psychoneuroimmunology (KPNI) asks how the nervous system, hormones, metabolism and the immune system work together. During Ramadan, all four change at the same time, in time with a shifted clock.

I see a fifth level in community and meaning. The international diabetes recommendations mention possible positive effects of Ramadan on stress, self-control and compassion. But they emphasize that there are hardly any studies on this. I take that as an honest reminder: not everything people experience during these weeks can be measured in a lab.

And now you know why I do not see Ramadan as a diet, but as four systems moving to a new rhythm.

Three levers for good fasting days

You do not have to put everything into practice at once. The following three levers are directions, not a treatment plan.

If you would like not only to read, but to look at your own situation together: below this article, you will find the option to book an appointment.

And now you know why good fasting days usually begin the night before.

Frequently asked questions about Ramadan fasting

Where this topic touches other areas

Ramadan fasting touches on fluids, your internal clock, movement, blood sugar and the nervous system. If you want to go deeper, these neighboring topics are worth a look.