The best things to do while fasting are activities that keep you occupied, support your body through the process, and don’t accidentally break your fast. Whether you’re doing a 16:8 intermittent fast or a longer multi-day fast, what you drink, how you move, and how you manage hunger all determine whether fasting feels productive or miserable.
Stay Hydrated With the Right Drinks
Water is your baseline, but you’re not limited to it. Black coffee, plain tea (green, black, herbal), and sparkling water are all safe choices that won’t trigger an insulin response or pull you out of a fasted state. The key rule: if it has calories, sugar, protein, or fat, it can break your fast. That means no cream in your coffee, no honey in your tea, and no flavored waters sweetened with fruit juice.
If you’re fasting longer than 18 to 24 hours, plain water alone isn’t enough. Your body loses electrolytes faster without food, and the deficit shows up as headaches, muscle cramps, fatigue, and brain fog. Aim for roughly 1,500 to 2,300 mg of sodium, 1,000 to 2,000 mg of potassium, and 300 to 400 mg of magnesium per day. You can get these through sugar-free electrolyte powders, a pinch of salt in your water, or magnesium supplements in capsule form. Avoid electrolyte drinks with added sugars or maltodextrin, which will break your fast.
Move Your Body, but Choose Wisely
Light to moderate exercise pairs well with fasting. Walking, yoga, stretching, and easy cycling are all good options that keep you active without draining your energy reserves. Many people find that a 20 to 40 minute walk is the single best way to push past a wave of hunger and reset their focus.
High-intensity workouts are a different story. Heavy weightlifting or intense interval training in a fasted state can leave you dizzy, shaky, or nauseous, especially if you’re new to fasting or past the 18-hour mark. If you do want to train hard, schedule it near the end of your fasting window so you can eat shortly afterward. Over time, your body adapts to exercising in a fasted state, but the first few sessions are typically the hardest.
One notable benefit of combining fasting with regular exercise: both independently boost a protein called BDNF, which supports memory, learning, and overall brain health. When you stack the two, the effects appear to compound. Animal studies consistently show that fasting upregulates BDNF and improves cognitive performance, and the combination with physical activity amplifies the signal through multiple pathways.
Use the Mental Clarity Window
Many people report a noticeable sharpening of focus after 12 to 16 hours of fasting. This isn’t placebo. As your body shifts from burning glucose to using ketones for fuel, your brain gets access to a cleaner, more stable energy source. This metabolic switch also triggers mild stress-response pathways that enhance brain performance and resilience.
This makes your fasting window a surprisingly good time for deep work: writing, reading, studying, planning, or any task that requires sustained concentration. If you have mentally demanding work to do, try scheduling it during the second half of your fast rather than defaulting to Netflix. Some fasters treat their morning fasting hours as their most productive block of the day.
Manage Hunger Instead of Fighting It
Hunger during a fast doesn’t build in a straight line. It comes in waves driven by ghrelin, a hormone your stomach releases on a schedule tied to your usual mealtimes. If you normally eat breakfast at 8 AM, you’ll feel a ghrelin surge around 8 AM whether you need food or not. The wave peaks, then passes, typically within 20 to 30 minutes.
Here’s what makes this manageable: research on humans shows that total ghrelin levels don’t actually increase after 24 hours of fasting. Your body doesn’t ramp up the hunger signal indefinitely. Instead, it keeps pulsing at your habitual meal times, and as you adapt to a fasting schedule, those pulses weaken. The first three to five days of any new fasting routine are the hardest. After that, your ghrelin patterns start to shift.
When a hunger wave hits, the most effective responses are drinking water or black coffee, going for a short walk, or switching to an engaging task. Sitting still while thinking about food is the worst possible strategy.
Watch Your Supplements
Not everything in your medicine cabinet is fasting-safe. Gummy vitamins almost always contain sugar, protein, or fat and will break your fast. Protein powder and branched-chain amino acids (BCAAs) both trigger an insulin response. Any supplement containing maltodextrin, pectin, cane sugar, or fruit juice concentrate has enough calories to pull you out of a fasted state.
What’s generally fine: standard capsule or tablet multivitamins without added sugars, fish oil in small amounts (though technically caloric, a single capsule is unlikely to trigger a meaningful insulin response), and magnesium or sodium supplements. If you take prescription medications with food, talk to your pharmacist about whether they can safely be taken on an empty stomach instead.
Prepare for Sleep Changes
Fasting raises cortisol levels. In humans, cortisol begins increasing immediately after fasting starts, and with multi-day fasts, the cortisol peak can shift from morning to afternoon or evening. That shift matters because elevated evening cortisol makes it harder to fall asleep and can reduce sleep quality.
If you’re doing time-restricted eating, this is a practical argument for eating earlier in the day rather than later. One study found that an early eating window (8 AM to 2 PM) produced only a slight cortisol increase in the morning, which is when cortisol is supposed to be high anyway. Fasting through the evening and night, on the other hand, can leave cortisol elevated right when you’re trying to wind down. If you notice trouble sleeping during your first week of fasting, this is likely why, and it typically improves as your body adjusts.
Know When to Stop
Some discomfort during fasting is normal: mild hunger, slight irritability, occasional low energy. But certain symptoms signal that your fast has crossed from beneficial stress into something your body can’t handle. Heart palpitations or a racing heart, extreme fatigue that doesn’t improve with rest, persistent nausea or vomiting, numbness or tingling in your hands and feet, and unexplained confusion are all signs of an electrolyte imbalance that requires you to eat.
These symptoms are more common during fasts longer than 24 hours, in hot weather, or if you’ve been exercising without replacing electrolytes. Breaking a fast for safety isn’t failure. You can always try again with better preparation.
Breaking Your Fast the Right Way
How you end your fast matters almost as much as how you spend it, especially after longer fasts of 24 hours or more. Your digestive system has been resting, and dumping a large, heavy meal into it can cause bloating, cramping, and nausea.
Start with something easy to digest: bone broth, a small portion of cooked vegetables, eggs, or a handful of nuts. Avoid highly processed foods, large amounts of sugar, or big portions for your first meal. Give yourself 30 to 60 minutes after your initial small meal before eating a full plate. For standard 16:8 intermittent fasting, this is less critical since your gut hasn’t been dormant for very long, but even then, starting with a balanced meal of protein, healthy fats, and vegetables rather than a pile of refined carbs will keep your blood sugar more stable and help you feel better for the rest of the day.