Going a full 24 hours without food is something your body can handle safely in most cases, but doing it comfortably takes some planning. The key factors are what you eat beforehand, what you drink during, how you manage the waves of hunger that come and go, and how you break the fast afterward. Here’s how to get through it without feeling miserable.
Eat the Right Meal Before You Start
Your last meal before the fast sets the tone for the next 24 hours. You want slow-burning fuel: complex carbohydrates like brown rice, potatoes, or whole-grain pasta paired with protein from meat, beans, or legumes. This combination takes longer to digest and keeps your blood sugar steadier in the early hours. A meal heavy in simple sugars or refined carbs will spike your blood sugar and then crash it, making the first stretch of fasting feel much harder than it needs to.
Aim to eat until you’re comfortably full, not stuffed. Overeating before a fast often backfires with bloating and discomfort that lingers into the early hours.
What Your Body Does Over 24 Hours
For the first 3 to 4 hours after your last meal, your body is still digesting and absorbing nutrients. Nothing unusual is happening yet. After that, you enter an early fasting state where blood sugar and insulin levels start to drop. Your body begins converting stored glycogen (a form of sugar kept in your liver) into usable energy. This phase carries you through roughly the first 18 hours.
Toward the end of that window, your liver’s glycogen stores run low, and your body ramps up a process called lipolysis, where fat cells are broken down into smaller molecules and burned for fuel. By the 18 to 24 hour mark, your body has largely shifted to drawing energy from fat and, to a lesser extent, protein. This is also when cellular cleanup processes begin to ramp up. In animal studies, markers of autophagy (the body’s way of recycling damaged cell components) increased more than threefold after 24 hours of food restriction.
Why Hunger Comes in Waves
One of the most useful things to know is that hunger doesn’t build in a straight line. The hormone ghrelin, which triggers the feeling of hunger, normally rises before your usual mealtimes and then drops afterward. When you skip a meal entirely, that spike still happens, but it passes. Most people find that the hardest points are around the times they’d normally eat. If you usually have lunch at noon, expect a strong hunger signal around noon that fades within an hour or two.
This wave pattern means you don’t need to white-knuckle through 24 straight hours of increasing misery. The hunger peaks, plateaus, and recedes. Staying busy during those windows (going for a walk, working on a project, even cleaning the house) makes them pass faster. Many people report that the stretch from roughly hour 16 onward actually feels easier than the middle of the day, because the body has settled into using stored fuel and ghrelin signals have quieted down.
What You Can Drink
Water is the foundation. You should be drinking it steadily throughout the day, not just when you feel thirsty. Beyond water, several beverages won’t meaningfully disrupt the fasted state.
- Black coffee and plain tea are fine and can help blunt appetite.
- Diet soda contains no calories and doesn’t provoke a measurable insulin response, though plain water or sparkling water is a better choice for hydration.
- A splash of cream or butter in coffee technically contains calories, but fat is the least insulin-stimulating nutrient. A small amount of high-fat dairy without added sugar won’t derail your fast.
- Stevia, monk fruit, and allulose are zero-calorie or near-zero sweeteners that have minimal to no effect on insulin. Allulose, in particular, has been shown to lower blood glucose without raising insulin at all.
- Bone broth contains some calories and a small amount of protein, but a mug or two is generally considered compatible with a fast and can help with electrolytes.
Keep Your Electrolytes Up
Most of the unpleasant side effects people experience during a one-day fast, such as dizziness, headaches, fatigue, and muscle cramps, come from electrolyte depletion rather than the lack of food itself. When insulin drops during fasting, your kidneys excrete more sodium, and potassium and magnesium follow it out.
For a 24-hour fast, aim to take in roughly 1,500 to 2,300 mg of sodium, 1,000 to 2,000 mg of potassium, and 300 to 400 mg of magnesium. The simplest approach is adding a pinch or two of salt to your water throughout the day. You can also use electrolyte packets or supplements designed for fasting. If you start feeling lightheaded, sip salted water and sit down. That symptom almost always resolves within minutes once you get sodium in.
Your Brain Will Probably Work Fine
A common worry is that skipping food for a day will leave you foggy and unable to concentrate. The research is more reassuring than you might expect. A controlled lab experiment that randomly assigned participants to different fasting lengths and then tested them with a standard cognitive ability assessment found no significant effect on mental performance from fasting. A separate review of studies looking at fasting up to 24 hours found no substantial effects on cognitive function, with the only notable change being a slightly slower finger-tapping speed in the longest-fasting group.
Broader reviews of intermittent fasting and cognition in healthy adults have reached no consensus that short fasts impair thinking. You may feel somewhat distracted during hunger peaks, but your actual capacity for reasoning, decision-making, and focus is unlikely to take a meaningful hit over a single day.
How to Break the Fast
The meal you break your fast with matters more than most people realize. Eating a large, heavy, or greasy meal after 24 hours without food commonly causes heartburn, bloating, and general digestive discomfort. Your digestive system has been essentially idle, and it needs a gentle restart.
Start with something small and easy to digest. Dates are a traditional choice for breaking fasts during Ramadan for good reason: a single Medjool date provides about 18 grams of quick-absorbing carbohydrates. Smoothies, fruit juice, or a small bowl of soup with lentils or rice are other good options. These give your body nutrition without overwhelming your gut.
After that first small portion, wait 30 to 60 minutes before eating a fuller meal. When you do eat more, lean toward lean proteins like fish or plant-based options rather than red meat, and go easy on fatty or spicy foods. Eat slowly and stop at comfortable fullness. Your appetite after a fast can be deceptively large, and eating too fast is the most common cause of post-fast digestive regret.
Who Should Skip This
A 24-hour fast is not appropriate for everyone. You should not attempt it if you have diabetes and require multiple insulin injections per day, if you take blood thinners that need to be taken every 12 hours with food, or if you have any unstable medical condition requiring IV fluids or blood transfusions. People with a history of eating disorders should also approach any form of deliberate food restriction with extreme caution, as fasting can reinforce harmful patterns around food.
Pregnant or breastfeeding women, children, and anyone who is underweight should not fast for 24 hours. If you’re on any prescription medication that’s meant to be taken with food, skipping meals for a full day can alter how that medication is absorbed and how it affects you.