The best way to fast depends on your experience level and goals, but most people start with a daily time-restricted approach: eat within an 8-hour window and consume nothing but water, plain coffee, or tea for the remaining 16 hours. This method, known as 16:8 fasting, is the most studied and sustainable entry point. From there, you can adjust the duration and frequency based on how your body responds.
Choose a Fasting Schedule That Fits Your Life
The most practical fasting method for beginners is the 16:8 pattern. You eat during an 8-hour window and fast for 16 hours, including sleep. Popular windows include 9 a.m. to 5 p.m., 12 p.m. to 8 p.m., or 7 a.m. to 3 p.m. The window you pick matters less than your ability to stick with it. If you naturally skip breakfast, a noon-to-8 p.m. window requires almost no lifestyle change. If you prefer early dinners, a 7 a.m. to 3 p.m. window works better. You can do this every day or just a few days per week.
The 5:2 method takes a different approach. You eat normally five days per week and limit yourself to roughly 500 to 600 calories on the other two days. Those two low-calorie days shouldn’t be back to back. This works well for people who don’t want to think about fasting every single day but still want the metabolic benefits of periodic calorie restriction.
OMAD (one meal a day) compresses your entire daily intake into a single meal, creating a roughly 23-hour fast. This is a more advanced protocol and not ideal for beginners, since eating enough nutrients in one sitting is genuinely difficult. Most people who do well with OMAD work up to it after months of shorter fasting windows.
What Happens in Your Body During a Fast
In the first 4 to 8 hours after your last meal, your body finishes digesting and absorbing food. Insulin levels gradually drop, which signals your cells to stop storing energy and start using it. By around 12 hours, your body has burned through most of its readily available sugar stores (glycogen) in the liver and begins shifting toward burning fat for fuel. This transition is when many people notice a shift in mental clarity or energy.
Between 18 and 24 hours, your body enters a deeper fat-burning state. Ketone production increases as fat is broken down more aggressively. Some people report reduced hunger at this stage because ketones themselves can suppress appetite.
A process called autophagy, where your cells break down and recycle damaged components, is one of the most talked-about benefits of fasting. Animal studies suggest autophagy ramps up significantly between 24 and 48 hours of fasting. However, according to the Cleveland Clinic, not enough research exists to pinpoint the exact timing in humans. The takeaway: a 16-hour fast likely triggers some degree of cellular cleanup, but the deeper benefits probably require longer fasts.
What You Can Drink Without Breaking Your Fast
Water is always fine. Plain black coffee and unsweetened tea are also safe choices during a fast. They contain essentially zero calories and don’t produce a meaningful insulin response. Adding cream, sugar, or flavored syrups will break your fast.
Artificially sweetened drinks are more complicated. Diet sodas, even with zero calories, can increase insulin resistance over time. If your goal is metabolic improvement, skip them during your fasting window. Sparkling water and mineral water are fine alternatives. Bone broth technically contains calories, so it breaks a strict fast, but some people use it during longer fasts (24+ hours) to maintain electrolyte balance while keeping calorie intake minimal.
Electrolytes Matter More Than You Think
Short fasts of 16 to 20 hours rarely cause electrolyte problems if you eat a balanced diet during your eating window. But if you’re fasting for 24 hours or longer, or fasting frequently, you need to pay attention to three minerals in particular.
- Sodium: 1,500 to 2,300 mg per day. This is critical for maintaining blood volume and hydration. A pinch of salt in your water can prevent headaches and dizziness.
- Potassium: 1,000 to 2,000 mg per day. Essential for heart rhythm and muscle function. Low potassium causes fatigue and cramping.
- Magnesium: 300 to 400 mg per day. Important for sleep quality, muscle relaxation, and preventing cramps.
You can get these through electrolyte supplements, mineral water, or simply adding a small amount of salt and a magnesium supplement to your water. Avoid electrolyte drinks with sugar or artificial sweeteners, which defeat the purpose.
How to Break a Fast Properly
After a 16- to 20-hour fast, you can eat a normal meal without much concern. Your digestive system hasn’t shut down, it’s just been resting. Start with something balanced: protein, healthy fats, and vegetables. Avoid diving straight into a large amount of refined carbohydrates or sugar, which can cause a sharp blood sugar spike and leave you feeling sluggish.
After fasts lasting 24 hours or more, ease back in. A small meal with easily digestible protein (eggs, yogurt, fish) and cooked vegetables works well. Give yourself 30 to 60 minutes before eating a larger meal. The longer you’ve fasted, the more gently you should reintroduce food. Eating a massive, carb-heavy meal after a 48-hour fast can cause bloating, nausea, and uncomfortable blood sugar swings.
Common Mistakes to Avoid
The biggest mistake new fasters make is compensating by overeating during their eating window. Fasting isn’t a free pass to eat anything. If you consume more calories than your body needs in 8 hours, you won’t lose weight regardless of how long you fasted.
Another common error is starting too aggressively. Jumping from three meals and two snacks per day straight into a 24-hour fast is uncomfortable and unnecessary. Start by pushing breakfast back an hour or two. Once you’re comfortable with a 14-hour overnight fast, extend it to 16. Your body adapts to fasting over days and weeks, and the hunger you feel in the first few days usually diminishes significantly by the end of the first week.
Exercising intensely during your first few fasts can backfire. Light movement like walking is fine and may even help your body shift into fat-burning mode faster. But heavy lifting or high-intensity cardio on an empty stomach, before you’re adapted, often leads to dizziness, poor performance, and excessive fatigue. Once you’ve been fasting consistently for two to three weeks, your body becomes more efficient at using fat for fuel and exercise tolerance improves.
Who Should Be Careful With Fasting
Fasting is not appropriate for everyone. People with diabetes face real risks from extended periods without food, particularly if they take insulin or medications that lower blood sugar. Blood sugar can drop dangerously low during a fast if medication timing isn’t adjusted.
People who take blood pressure or heart disease medications may be more prone to imbalances in sodium, potassium, and other minerals during fasting. Anyone who needs to take medication with food to avoid nausea or stomach irritation will also have difficulty with longer fasting windows.
If you’re already at a low body weight, fasting can push you into a range that affects bone density, immune function, and energy levels. And for anyone with a history of disordered eating, the rigid rules around fasting can trigger or worsen unhealthy patterns. In these cases, the risks clearly outweigh the potential benefits.