Fasting means voluntarily going without food for a set period, then eating during a designated window. The most common approach for beginners is time-restricted eating, where you fast for 16 hours and eat within an 8-hour window each day. But there are several methods, and the right one depends on your schedule, your goals, and how your body responds. Here’s how each one works in practice.
Choose a Fasting Method
Most people who fast follow one of three popular schedules. They all work by limiting when you eat rather than obsessing over what you eat, though food quality still matters.
16:8 (time-restricted eating): You eat during an 8-hour window and fast for the remaining 16 hours. A common setup is eating between 11 a.m. and 7 p.m., which essentially means skipping breakfast and stopping eating after dinner. This is the easiest method to start with because most of your fasting hours happen while you sleep.
5:2: You eat normally five days a week and cap your intake at 500 calories on the other two days. On those low-calorie days, most people split their food into a 200-calorie meal and a 300-calorie meal. The two fasting days shouldn’t be back-to-back; spacing them out (say, Tuesday and Thursday) makes the method more sustainable.
One meal a day (OMAD): You eat a single large meal within roughly a one-hour window and fast for the remaining 23 hours. This is the most aggressive common method and generally not recommended as a starting point.
What You Can Drink While Fasting
During your fasting window, stick to zero-calorie and minimal-calorie beverages. Water (plain or sparkling) is the obvious choice and keeps you hydrated, which helps manage hunger. Black coffee and unsweetened tea are also fine. Zero-calorie electrolyte drinks without artificial sweeteners work too, especially if you’re fasting for longer stretches or exercising.
Anything with calories, sugar, cream, or artificial sweeteners can disrupt the fasted state. That means no milk in your coffee, no juice, no diet soda. If it has a nutrition label with calories on it, save it for your eating window.
How to Start Your First Fast
The simplest way to begin is with the 16:8 method. Pick an 8-hour eating window that fits your life. If you normally eat dinner around 7 p.m., that means your first meal the next day would be at 11 a.m. For the first few days, you’ll likely feel hungry in the morning. This is mostly habit, not genuine caloric need, and it typically fades within a week as your body adjusts.
Start by pushing breakfast back by an hour or two, then gradually extend until you reach the full 16-hour fast. There’s no rule that says you need to jump straight into the deep end. Some people ease in over a week, going from a 12-hour fast to 14, then to 16. Others find it easier to commit fully from day one and ride out the adjustment period.
During your eating window, eat balanced meals with enough protein, healthy fats, fiber, and complex carbohydrates. Fasting is not an excuse to binge. The calorie reduction happens naturally for most people because they’re simply eating fewer meals, but cramming a day’s worth of junk food into 8 hours will undermine any benefit.
What Happens in Your Body During a Fast
In the first several hours without food, your body burns through its stored glucose (glycogen) for energy. Once those reserves run low, typically 12 to 16 hours in, your body shifts toward burning stored fat for fuel. This metabolic shift is one reason fasting can be effective for fat loss.
With longer fasts (24 hours and beyond), your body ramps up a cellular recycling process where damaged cell components are broken down and reused. Animal studies suggest this process kicks in somewhere between 24 and 48 hours of fasting, though researchers haven’t pinpointed the exact timing in humans. For most people doing daily 16:8 fasting, this deeper cellular cleanup isn’t the primary benefit. The practical gains come from the metabolic shift and reduced overall calorie intake.
Fasting and Weight Loss
Fasting works for weight loss primarily because it reduces how much you eat. A Harvard-covered study of 165 people compared a fasting group (who ate only 20% of their usual calories on three fasting days per week) with a group that simply cut daily calories by 34%. After one year, the fasting group lost about 6 more pounds on average than the calorie-restriction group.
That said, the difference isn’t dramatic. Both approaches lead to weight loss. Fasting’s advantage for many people is behavioral: it’s simpler to follow a rule about when to eat than to count every calorie at every meal. If traditional calorie counting works well for you, fasting won’t offer a magic metabolic edge. It’s a different tool that some people find easier to stick with.
Exercise While Fasting
You can exercise during a fast, but the timing and type of exercise matter. Light cardio, walking, and moderate workouts are generally well-tolerated in a fasted state. Some people prefer training near the end of their fasting window and then eating shortly after.
If building or maintaining muscle is a priority, resistance training paired with fasting can preserve muscle mass. A systematic review found no significant differences in lean mass between people who did resistance training while fasting and those who trained on a normal eating schedule. The key is making sure you get enough total protein during your eating window. Research on muscle growth suggests that spreading protein across 3 to 4 meals, at roughly 0.25 to 0.3 grams per kilogram of body weight per meal, supports better muscle repair than eating it all in one sitting. For a 160-pound person, that works out to about 18 to 22 grams of protein per meal.
This is one area where OMAD and very narrow eating windows have a disadvantage. Cramming all your protein into a single meal is less effective for muscle building than distributing it across two or three meals within your window.
How to Break a Fast
For standard 16:8 fasting, breaking your fast doesn’t require much ceremony. A normal, balanced meal works fine. Some people find that very heavy, greasy, or sugary foods on an empty stomach cause bloating or discomfort, so starting with something moderate is a good habit. A meal with protein, some vegetables, and a healthy fat source is a solid choice.
If you’ve fasted for 24 hours or longer, your digestive system may be more sensitive. Start with something easy to digest: a small portion of soup, eggs, cooked vegetables, or a smoothie. Give yourself 30 to 60 minutes before eating a larger meal. The longer the fast, the more gently you should reintroduce food.
Common Mistakes to Avoid
- Overeating during your window. Fasting creates a natural calorie deficit, but only if you don’t compensate by eating significantly more during your meals.
- Not drinking enough water. A surprising amount of your daily water intake normally comes from food. When you skip meals, you need to consciously drink more.
- Starting too aggressively. Jumping straight into OMAD or 24-hour fasts without experience often leads to headaches, irritability, and quitting within days.
- Ignoring food quality. Fasting narrows the window, but what you eat during that window still determines your nutrition. Prioritize whole foods, adequate protein, and enough fiber.
- Fasting every single day without flexibility. Missing your window occasionally is fine. Rigid adherence that causes stress or social isolation works against you long-term.
Who Should Be Cautious
Fasting isn’t appropriate for everyone. People with a history of eating disorders may find that restricting eating windows triggers unhealthy patterns. Pregnant or breastfeeding women have increased caloric and nutritional needs that fasting can undermine. People with diabetes, particularly those on insulin or medications that lower blood sugar, face real risks from extended periods without food. Children and teenagers are still growing and generally shouldn’t restrict their eating windows.
If you’re on any medication that needs to be taken with food at specific times, fasting schedules may conflict with your prescription. Adjusting your eating window to accommodate medication timing is usually straightforward, but it’s worth thinking through before you start.