What is intermittent fasting? It’s an eating pattern that alternates between times when you eat and times when you fast. Instead of focusing first on what foods to eat, this fasting approach focuses on when you eat. Some intermittent fasting rules limit eating to certain hours each day, while others include lower-calorie or fasting days during the week. (1)
An IF schedule alternates between fasting and eating windows. The most popular intermittent fasting plan is 16/8: fast 16 hours, eat in an 8-hour window such as 12 p.m. to 8 p.m. (1)
Intermittent fasting is not for everyone. If you’re pregnant, breastfeeding, under 18, have a history of eating disorders, take diabetes medication, have a history of low blood sugar, or take medicine that needs to be taken with food, talk with a healthcare professional before trying it. (11,12)
How Does Intermittent Fasting Work?
During an intermittent fasting window, you avoid or greatly limit calories for a set amount of time. During your eating window, you eat meals and snacks. (2)
There are several ways to follow intermittent fasting rules effectively. Some people fast overnight and eat during a shorter daytime window. Others use lower-calorie days or full fasting days during the week. (1,2)
For some people, having a clear eating window can make it easier to notice things like late-night snacking or grazing. But intermittent fasting is not magic, rather it’s one tool among many for managing weight, not a guaranteed fix. See “Is Intermittent Fasting Healthy?” below for what the research actually shows.
Common Intermittent Fasting Schedules
There is no single best intermittent fasting schedule for everyone. The right fit depends on your health history, schedule, appetite, workouts, sleep, and how you feel when you go longer without food.
12/12 Fasting
A 12/12 intermittent fasting schedule means fasting for 12 hours and eating during a 12-hour window. This is often a gentle place to start because most of the fasting window happens while you sleep. Eating for about 12 hours and then fasting for about 12 hours is likely safe for most people. (15)
Example 12/12 windows:
- 7 a.m. to 7 p.m.
- 8 a.m. to 8 p.m.
- 9 a.m. to 9 p.m.
- 10 a.m. to 10 p.m.
These intermittent fasting times may work well if you like breakfast, eat dinner with family, or want a less restrictive routine.
16/8 Fasting
The 16/8 method is an intermittent fasting schedule of 16 hours and eating during an 8-hour window. (1)
Example 16/8 windows:
- 10 a.m. to 6 p.m.
- 11 a.m. to 7 p.m.
- 12 p.m. to 8 p.m.
- 1 p.m. to 9 p.m.
This is one of the most well-known fasting patterns. Most members who use MyFitnessPal’s Intermittent Fasting Tracker choose the 16:8 pattern. It’s one of three intermittent fasting hours the Tracker supports (12:12, 14:10, and 16:8) so you can log your fasting window right alongside meals, water, and exercise.
5:2 Fasting
The 5:2 method usually means eating in your usual pattern five days a week and eating much less on two nonconsecutive days. Some versions of this intermittent fasting plan use about 500 to 600 calories on lower-calorie days. (1)
Example 5:2 patterns:
- Lower-calorie days on Monday and Thursday
- Lower-calorie days on Tuesday and Friday
- Lower-calorie days on Wednesday and Saturday
- Lower-calorie days on Sunday and Thursday
These intermittent fasting rules can feel more intense than daily fasting schedules. If lower-calorie days leave you feeling shaky, distracted, or overly hungry, it may not be the right fit for you.
Eat-Stop-Eat
Eat-Stop-Eat usually means fasting for a full 24 hours once or twice a week, then eating in your usual pattern on non-fasting days. Full-day fasting is one form of intermittent fasting. (1)
Example Eat-Stop-Eat windows:
- Dinner Monday to dinner Tuesday
- Lunch Wednesday to lunch Thursday
- Breakfast Friday to breakfast Saturday
- Dinner Sunday to dinner Monday
Longer intermittent fasting hours are more restrictive than 12/12 or 16/8. If you have a medical condition, take medication, or have a history of disordered eating, check with a healthcare professional before trying any fasting plan. (11,12)
Alternate-Day Fasting
Alternate-day fasting means alternating fasting or very-low-calorie days with regular eating days. Some versions involve very few or no calories on fasting days. (1)
Example alternate-day intermittent fasting times:
- Fast Monday, eat Tuesday, fast Wednesday
- Lower-calorie Tuesday, regular Wednesday, lower-calorie Thursday
- Fast every other weekday, eat normally on weekends
- Modified fast every other day with a small meal on fasting days
This can be hard to keep up. It may also not be a good idea for people who need to eat regularly for medical, medication, or personal reasons. (11)
OMAD
OMAD stands for “one meal a day.” It usually means eating one meal during a short window and fasting the rest of the day. It is a more restrictive form of fasting.
Example intermittent fasting hours under OMAD:
- 9 a.m. to 8 a.m. (23 hours)
- 1 p.m. to 12 p.m. (23 hours)
- 4 p.m. to 3 p.m. (23 hours)
- 7 p.m. to 6 p.m. (23 hours)
Because OMAD is so restrictive, it may be difficult to sustain long-term. A less restrictive intermittent fasting schedule may be easier to combine with balanced meals, workouts, family dinners, and time with friends.
Is Intermittent Fasting Healthy?
Intermittent fasting can be a healthy routine for some people, but it depends on the person, the schedule, and what they eat during eating windows.
Potential Intermittent Fasting Benefits
Joanna Gregg, a registered dietitian with MyFitnessPal, says fasting “might be especially beneficial for individuals who struggle with late-night snacking or overeating during the day.” Having set intermittent fasting hours can naturally lower how much people eat overall.
That calorie-limiting effect works alongside another mechanism. During a fasting window, the body uses up its stored sugar and starts burning fat for energy instead. This may support weight loss, including loss of visceral fat, which is the type stored around internal organs and linked to a higher risk of heart disease and type 2 diabetes. (14,6,7)
Fasting for 8 to 16 hours has also been linked to improved inflammation markers and insulin sensitivity. That may help lower the risk of chronic conditions such as diabetes. (6,10)
Side Effects
Intermittent fasting can cause side effects, especially in the early days as your body adjusts to a new eating pattern. The most common include headaches, dehydration, blood sugar swings, fatigue, and dizziness. Hunger during fasting periods may also disrupt sleep. (12)
These effects often ease once your body adapts. Staying hydrated and eating nutrient-dense meals during your eating window can help minimize them.
Who Should Be Careful
An intermittent fasting schedule isn’t safe for everyone. Gregg cautions that people with certain health conditions (including type 1 diabetes) or who are pregnant or breastfeeding should consult a healthcare provider before trying intermittent fasting. Fasting can cause blood sugar to drop to unsafe levels for these groups. (1)
It’s also worth managing expectations, even for people it’s a good fit for. Intermittent fasting isn’t a magic solution for weight loss — it mainly works by helping people eat fewer calories overall. Very restrictive plans that are hard to stick with aren’t necessarily more effective than modest, sustainable changes to calorie intake.
What the Research Says
The research backs this up, to a point. A large 2022 review found that eating within a set window was linked to drops in body weight and body fat in adults. (4)
A 2024 study saw similar results in adults with health risks like high blood sugar and extra belly fat. After three months of eating within an 8- to 10-hour window, they had small improvements in blood sugar, weight, and belly fat. (14)
But the evidence on intermittent fasting benefits is far from settled. One well-known study found the 16/8 method didn’t lead to more weight loss or better heart and blood sugar health than eating throughout the day. (5)
Taken together: intermittent fasting is a structure, not a guarantee. It may help if it makes your routine simpler. It may not help if it makes you feel unwell, overly restricted, or disconnected from hunger and fullness cues.
What Actually Determines Your Results
Food choices, portions, protein, fiber, sleep, stress, activity, and medical history all affect progress. Research on weight-loss strategies points to the same conclusion: the best plan is the one you can realistically stick with. (8)
If weight management is your goal, tracking for a short period may help you spot patterns. MyFitnessPal can help you compare meal timing, calories, protein, fiber, and water intake so you can see whether your fasting routine is supporting your goals.
What Can You Drink While Fasting?
During intermittent fasting times, most plans only calorie-free drinks, since consuming calories signals your body to end a fasted state. (2)
Common fasting-window drink options include:
- Water
- Plain sparkling water
- Black coffee
- Unsweetened tea
- No-calorie electrolyte drinks
Drinks with calories, such as juice, soda, milk, sweetened coffee drinks, smoothies, alcohol, or creamers, are usually saved for the eating window. If you take medication or supplements that need to be taken with food, ask your healthcare professional how to handle them while fasting.
What Should You Eat During Eating Windows?
Intermittent fasting does not tell you what to eat. That part still matters.
A simple place to start is with nutrient-dense foods that help you feel full, such as lean proteins, fruits, vegetables, whole grains, and healthy fats. Fruits and vegetables in particular are linked to a range of health benefits including reduced disease risk and better overall health. U.S. Dietary Guidelines recommend foods like these as the foundation of a balanced diet. . (13,3)
You do not have to make every meal perfect during your intermittent fasting hours. The goal is to make your eating window nourishing enough that fasting does not leave you feeling depleted.
Who Should Avoid Intermittent Fasting?
Intermittent fasting may not be appropriate for people who:
- Are pregnant or breastfeeding
- Are under 18
- Have a history of eating disorders
- Take medicine for diabetes
- Have a history of low blood sugar
- Take medications that must be taken with food
- Have a medical condition that requires regular meals or snacks (11,12)
Frequently Asked Questions (FAQs)
- What is intermittent fasting?
Intermittent fasting is an eating pattern that cycles between fasting periods and eating periods. Some schedules limit eating to certain hours each day, while others use fasting or lower-calorie days during the week. (1)
- Is intermittent fasting healthy?
It can be healthy for some people, but it is not right for everyone. Research suggests that an intermittent fasting schedule may have some short-term benefits for body weight and a few other health numbers, but results are mixed and we still don’t know much about the long-term effects. (4,5)
- Does intermittent fasting work?
Intermittent fasting may help some people lose weight, but it does not work better for everyone than other eating patterns. A 2022 review found small weight changes with fasting schedules, while one 16/8 study found no significant advantage for weight loss compared with standard eating patterns. (4,5)
- How does intermittent fasting affect metabolism?
Fasting on a schedule may affect some health numbers, including blood sugar, insulin, and cholesterol, and may reduce inflammatory markers — though results vary across studies and populations. (6,9,10)
- How long does it take for 16/8 intermittent fasting to work?
There is no guaranteed timeline. In one 12-week study, the 16/8 intermittent fasting schedule did not lead to much more weight loss than eating throughout the day. Some people may notice changes in their routine or hunger sooner, but weight and health changes depend on your whole eating pattern, not just the fasting window. (5)
- What can you drink while fasting 16/8?
During intermittent fasting hours, people usually drink water or calorie-free drinks, since calories are what signal the body to end a fast. Common choices include water, plain sparkling water, black coffee, and unsweetened tea. (2)
- What is the best intermittent fasting window to lose belly fat?
There’s no fasting window proven best for losing belly fat specifically. One 2024 study found small improvements in belly fat after three months of eating within an 8- to 10-hour window, but research on intermittent fasting benefits overall shows mixed results of fasting for weight loss, and a fasting window alone doesn’t guarantee fat loss. (14,4,5)
- How long should I fast to lose weight?
There’s no required length of intermittent fasting times. Many people start with a 12-hour overnight fast before trying 14/10 or 16/8; stricter plans aren’t right for everyone. (15)
- Can you drink coffee while fasting?
Yes, black coffee is allowed during intermittent fasting hours.
Find Your Fasting Pattern in MyFitnessPal
If you want help finding intermittent fasting rules that fit your routine, MyFitnessPal’s Intermittent Fasting Tracker supports three patterns (12:12, 14:10, and 16:8) so you can log your fasting window right alongside your meals, water, and workouts.
Bottom Line
Intermittent fasting is an eating schedule, not a complete nutrition plan. It may help some people manage weight or simplify meal timing, but research does not show that it works better for everyone than other eating patterns. (4,5)
If you try it, start with a gentle schedule, pay attention to how you feel, and eat enough nourishing food during your eating window. If you are pregnant, breastfeeding, have a history of eating disorders, take diabetes medication, have low blood sugar, or have a medical condition, talk with a healthcare professional before fasting. (11,12)
Originally published December 30, 2024; Updated August 11, 2026
The post Intermittent Fasting: What It Is, How It Works & Fasting Schedules appeared first on MyFitnessPal Blog.
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