16/8 window: how to fit it into your day

Sixteen hours is not a magic number, but a convenient one. During this time, the body has time to use up its liver glycogen stores and switch to fat: according to Harvard Health, the switch from the “fed” state to the “fasted” state begins approximately 5-6 hours after eating, and after 12-14 hours without food it is in full swing. Another 2-4 hours give the body time to work in this state without turning the day into an ordeal.

Shorter windows work too. In Анастасии’s method, the basic option is an 8-10-hour window and a 14-16-hour break: the difference between 14/10 and 16/8 for health and weight is small, but the difference in convenience is noticeable. If 16 hours are difficult, consistent 14 is better than heroic 16 three days a week. All the options are covered in the overview of intermittent fasting schedules.

Longer windows—18/6, 20/4, “one meal a day”—are a different story. For most people, they provide no additional benefit, but they significantly increase the risk of not eating enough protein and overeating in the evening.

Don’t start with breakfast. Start with dinner: it’s the most “social” meal, and the hardest one to move. Check what time you usually finish eating in the evening, and count back eight hours from that time — that will be your first meal.

Finish dinner at 20:00 — your first meal is at 12:00. Eat dinner at 18:00 — you can eat from 10:00. In Анастасии’s method, the schedule looks like this: 10:00, 13:00 and 18:00, three meals in an 8-hour window, with nothing in between. This is also how the basic intermittent fasting schedule described in our main article is structured.

The only thing that’s important to check is that sleep should fall entirely within the pause. If you go to bed at one in the morning but finish dinner at 18:00, the evening will be long and hungry. In that case, shift the entire window two hours later.

If you’re starting from scratch, don’t set 16/8 on the first day: the practical approach is one hour per step over three weeks. It is described in the article how to start intermittent fasting.

For the first 4-5 hours after eating, your body runs on what you ate: glucose and insulin levels are elevated, and absorption is underway. After that, the liver starts releasing stored glycogen — it lasts for about 12-14 hours, depending on how many carbohydrates were in your last meal. On a low-carbohydrate diet, this supply is smaller, so the switch to fat happens earlier and more smoothly.

At around the 12th hour, ketone production increases — ketones are fuel that the liver makes from fat. This is the very moment the fasting window is meant to create. Researchers at Johns Hopkins call this a “metabolic switch” and note that the body needs 2-4 weeks to adapt to the new schedule: irritability and hunger may occur at first, but then they go away.

A wave of hunger during the fasting window usually arrives at the time when you used to eat and subsides on its own after 20-30 minutes. Why this happens and how to tell real hunger from habit are explained in the article hunger during the fasting window.

While the window is closed, you only need water, coffee, and salt — what exactly is allowed and what already counts as food is explained in the article what you can drink during the fasting window. Workouts during the fasting window are allowed, but with some caveats — they are covered in the article fasting and workouts. And if the night turns into a battle with the refrigerator, the cause is usually dinner and bedtime: read about it in night hunger and sleep.

The main mistake with 16/8 is not hunger but undereating. The window is short, there are only two or three meals, and if each of them is “light,” you do not get enough protein, fats, or energy over the course of the day. After a week, fatigue sets in, and the person decides that fasting is not for them. In fact, it was the deficit that did not suit them.

The method’s guideline: 100-130 g of a protein food at each meal, half the plate — vegetables, a quarter — protein, a quarter — fats. You need to eat your entire daily intake until comfortably full, not until you feel “slightly hungry.” How to put together your first plate after a break so as not to overeat or remain hungry is covered in the article about the first meal after a break.

Once 16/8 becomes a habit, many people notice that three meals within the window are no longer necessary — two are enough. This is a normal next step, but it is worth making the transition consciously: read more about it in two meals a day.

A year-long study published in the New England Journal of Medicine in 2022 compared two groups of people with excess weight: both ate with the same calorie deficit, but one fit their meals into an 8-hour window, while the other ate whenever they wanted. After a year, the first group lost an average of about 8 кг, while the second lost about 6,3 кг, and the difference was not statistically significant. The conclusion is simple: the window itself does not cause weight loss, but it helps maintain a deficit without counting — eating less is easier when you simply eat less often.

A review by Harvard Health cites the same figures: intermittent fasting produces a moderate average weight loss of 3-8% of initial body weight and works best alongside sufficient protein and strength training, so that fat is lost rather than muscle.