16:8 Intermittent Fasting: The Most Popular Schedule Explained

Quick answer: 16:8 intermittent fasting means you eat within an 8-hour window and fast for the remaining 16 hours each day. It is the most widely practiced fasting schedule because it balances meaningful metabolic benefits with real-world sustainability, and most people can adapt to it within a week.

Why 16:8 Dominates the Fasting World

If you have heard of intermittent fasting, there is a good chance 16:8 was the first protocol mentioned. It occupies the sweet spot between doing something meaningful for your metabolism and not turning every social meal into a logistical nightmare. The schedule was popularized by Martin Berkhan's Leangains approach in the early 2010s, but it has since become the default recommendation from researchers, dietitians, and fasting apps alike.

The reason is straightforward: 16 hours is long enough to deplete liver glycogen stores and shift the body toward fat oxidation, yet short enough that most people can achieve it simply by skipping breakfast or pushing it back a few hours. A 2020 trial published in Cell Metabolism by Wilkinson et al. found that restricting eating to a 10-hour window improved cardiometabolic markers in patients with metabolic syndrome. Narrowing that window to 8 hours intensifies those benefits without dramatically increasing difficulty.

How the 16:8 Schedule Works

The mechanics are simple. Pick an 8-hour eating window that fits your life. Common choices include:

10 AM to 6 PM -- works well for people who prefer an earlier dinner
12 PM to 8 PM -- the most popular window; effectively skipping breakfast
8 AM to 4 PM -- an early eating window that aligns with circadian rhythm fasting research

During your 8-hour window, you eat your normal meals. During the 16-hour fast, you consume only water, black coffee, or plain tea. No calories.

There is no magic in these exact hours. The principle is consistency. Your body adapts to predictable feeding windows by adjusting hunger hormones, particularly ghrelin, which tends to peak at habitual meal times. After about 5 to 7 days on a consistent schedule, most people report that the fasting period feels natural rather than forced.

What Happens During a 16-Hour Fast

Understanding the physiology helps you trust the process, especially during the first week when hunger can feel disproportionate to what is actually happening inside.

Hours 0 to 4 (Post-meal): Your body is digesting and absorbing nutrients. Insulin is elevated, directing glucose into cells for energy and storage.

Hours 4 to 8: Insulin levels drop. Your body begins tapping into glycogen -- stored glucose in the liver and muscles -- for energy.

Hours 8 to 12: Glycogen stores start to deplete. The metabolic shift toward fat oxidation begins. Levels of norepinephrine rise slightly, which helps mobilize fatty acids from adipose tissue.

Hours 12 to 16: You are now in a fasted state where fat oxidation is the primary fuel source. Research by Anton et al. (2018) in the journal Obesity describes this as the "metabolic switch," where the body transitions from glucose-based to fat-based energy. Human growth hormone levels also begin to rise, which supports muscle preservation during the fast.

This is why 16 hours matters. Shorter fasts -- say 12 or 13 hours -- may not fully engage this metabolic switch in most people. The 14:10 schedule is a great stepping stone, but 16:8 is where the metabolic benefits become more pronounced.

Evidence-Based Benefits of 16:8 Fasting

The research on time-restricted eating has expanded rapidly. Here is what the evidence supports:

Weight and Fat Loss

A 2018 study in Nutrition and Healthy Aging by Gabel et al. found that participants following a 16:8 protocol for 12 weeks lost an average of 3% of body weight without calorie counting. The effect was driven primarily by a natural reduction in caloric intake -- eating within a shorter window tends to reduce overall consumption by 300 to 500 calories per day.

Improved Insulin Sensitivity

Sutton et al. (2018) published a controlled trial in Cell Metabolism showing that early time-restricted feeding (an 8-hour eating window ending by mid-afternoon) improved insulin sensitivity, beta-cell function, and blood pressure in men with prediabetes, even without weight loss. This suggests the timing itself has metabolic value beyond calorie reduction.

Cardiovascular Health

A systematic review by Regmi and Heilbronn (2020) in Annual Review of Nutrition concluded that time-restricted eating protocols consistently reduce blood pressure, LDL cholesterol, and triglycerides in overweight adults.

Reduced Inflammation

Moro et al. (2016) studied resistance-trained males on a 16:8 schedule and found significant reductions in inflammatory markers (IL-6, TNF-alpha) after 8 weeks, alongside maintained muscle mass and reduced fat mass.

How to Start 16:8 Fasting

If you are new to fasting, jumping straight to 16 hours can feel aggressive. Here is a practical ramp-up:

Week 1: Start with a 12 or 14-hour fast. If you normally eat dinner at 8 PM, simply delay breakfast until 10 AM.

Week 2: Push your first meal to 11 AM or noon. You are now at 15 to 16 hours.

Week 3 onward: Lock in your preferred 8-hour window and keep it consistent.

A few things that make the transition easier:

Stay hydrated. Thirst often masquerades as hunger. Sparkling water, black coffee, and herbal tea are all fine during the fast.
Keep busy during the morning. Hunger is partly psychological. If you are engaged in work or activity, the fasting hours pass quickly.
Eat enough during your window. This is not a starvation diet. If you under-eat during your 8 hours, you will feel terrible and quit. Aim for your normal caloric needs.
Be flexible when life demands it. Breaking your fast an hour early for a family breakfast will not undo your progress. Consistency over perfection.

For a broader introduction, the beginner's guide to intermittent fasting covers the fundamentals in depth.

Common Mistakes to Avoid

Overeating during the window. Some people treat the 8-hour window as a free pass. While 16:8 does not require calorie counting, consuming 3,000 calories of processed food in 8 hours will not produce the results you are looking for.

Choosing the wrong window for your schedule. If you eat dinner with your family at 7:30 PM every night, an eating window of 8 AM to 4 PM is going to create friction. Pick a window that works with your actual life.

Not adjusting on training days. If you exercise intensely, you may want to shift your eating window to include a post-workout meal. Fasted training is fine for many people, but recovery requires fuel.

Expecting overnight results. The metabolic and body composition changes from 16:8 fasting accumulate over weeks and months. Most studies showing significant results ran for 8 to 12 weeks minimum.

16:8 vs. Other Fasting Schedules

The 16:8 protocol sits in the middle of the fasting spectrum. If you find it easy after a few weeks, you might consider progressing to an 18:6 schedule, which extends the fasted state and deepens fat oxidation. If 16:8 feels too restrictive, the 14:10 schedule offers a gentler alternative while still delivering meaningful benefits.

For a side-by-side comparison of all major fasting protocols, see our guide to the best intermittent fasting schedule for your goals.

Who Should (and Should Not) Try 16:8

16:8 is appropriate for most healthy adults. It is particularly well-suited for people who want to lose weight without tracking calories, improve metabolic health markers, or simply bring more structure to their eating habits.

It is not recommended for:

Pregnant or breastfeeding women
People with a history of eating disorders
Anyone with Type 1 diabetes or on insulin (without medical supervision)
Children and adolescents

If you have any medical conditions, talk to your doctor before starting.

How Fasted Helps

Tracking your fasting window manually gets old fast. Fasted gives you a simple timer that counts down your 16-hour fast, sends reminders when your eating window opens and closes, and tracks your streaks so you can see your consistency over time. The app supports 16:8 as a preset schedule, and you can adjust your eating window anytime. Weight tracking and meal logging let you connect your fasting routine to actual results, and the stats dashboard shows patterns you would never catch on your own.

Frequently Asked Questions

Can I drink coffee during the 16-hour fast?

Yes. Black coffee, plain tea, and water are fine. Adding milk, cream, or sugar breaks the fast because they trigger an insulin response. A splash of cream (under 10 calories) is debated, but to be safe, keep it black.

Will I lose muscle on 16:8?

Unlikely, provided you eat adequate protein during your eating window (1.6 to 2.2 grams per kilogram of body weight) and maintain resistance training. The Moro et al. (2016) study found no muscle loss in trained individuals following 16:8 for 8 weeks.

How quickly will I see results?

Most people notice reduced bloating and improved energy within the first week. Measurable weight loss typically becomes apparent by weeks 2 to 4. Significant body composition changes usually require 8 to 12 weeks of consistent practice.

Can I do 16:8 every day?

Yes. Unlike extended fasting protocols, 16:8 is designed to be a daily practice. Most research studies use daily adherence, and the protocol is considered safe for long-term use in healthy adults.

Is it better to skip breakfast or dinner?

Research on circadian rhythm fasting suggests earlier eating windows may offer metabolic advantages. However, the best window is the one you will actually stick to. Skipping breakfast is more practical for most people's social and work lives.