In short
16:8 intermittent fasting means spending 16 hours of the day without calories and fitting every meal into an 8-hour window — eating between 12:00 and 20:00, for example, and taking only water, black coffee and unsweetened tea outside it. It tends to produce weight loss not through any metabolic trick but because fewer meals means total calorie intake falls on its own.
What 16:8 actually means
Intermittent fasting regulates when you eat rather than what you eat. In a 16:8 pattern the day is split into a 16-hour fast and an 8-hour eating window. The 7-8 hours you spend asleep count towards the fast, so in practice all you have to do is delay breakfast or bring dinner forward.
Common windows are 12:00-20:00, 11:00-19:00 or 10:00-18:00. Which you pick depends on which fits your day — no window has been shown to be decisively better than another.
What you can drink while fasting
The point of the fasting window is to take in too little energy to trigger a meaningful insulin response. In practice the accepted threshold is close to zero calories.
- Allowed: water, sparkling water, plain black coffee, unsweetened herbal and black tea.
- Breaks the window: coffee with milk, fruit juice, anything with honey or sugar, "just one bite" snacks.
- Debated: drinks with sweeteners. They add no calories but can prompt appetite in some people — go by your own experience.
Why it works
Most controlled studies point the same way: when calorie intake is matched, there is no meaningful difference in weight loss between intermittent fasting and conventional calorie restriction. The fast itself does not add fat burning.
It still works for plenty of people, because it offers a behavioural shortcut. An eight-hour window usually holds two meals, at most three; evening grazing disappears by itself and total intake drops. Having a clock to watch instead of numbers to count improves adherence noticeably for some people.
The first fortnight, and the usual mistakes
Hunger, headaches and difficulty concentrating are normal in the first few days and usually settle within 7-10 days. Keeping fluid and salt intake up reduces those complaints considerably.
The real risk is compensating the moment the window opens. Someone eating 2,500 calories in eight hours has taken in more energy than someone eating 2,000 across twelve, and the fast has achieved nothing.
- Build the first meal of the window around protein and fibre — satiety lasts longer.
- In the first week, train inside the window rather than doing heavy sessions fasted.
- Do not abandon the window entirely at weekends; the benefit comes from consistency.
- Do not pick a window that clashes with your sleep — eating late degrades sleep quality.
Who should not do it
Intermittent fasting is not suitable for everyone, and in some situations it is clearly harmful.
- Anyone pregnant or breastfeeding.
- Anyone under 18.
- Anyone with a history of disordered eating — restriction-based patterns can reactivate it.
- People with type 1 diabetes, or anyone on medication timed to meals (particularly insulin or sulfonylureas), without medical supervision.
- People who are underweight or trying to gain weight.
Frequently asked questions
Can I drink coffee while fasting?
Plain black coffee is fine; its calorie content is negligible. The moment you add milk, cream or sugar you have opened the window.
Will 16:8 make me lose muscle?
If your protein intake is adequate and you do resistance training, the risk is low. The variables that matter are total daily protein and the training stimulus, not the length of the fast.
Do I need the same window every day?
Not strictly, but a fixed window makes the habit easier to build and lets hunger signals settle into a rhythm. Shifting it occasionally for social reasons does no harm.
Sources
- 1.
Lowe DA, Wu N, Rohdin-Bibby L, et al. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men with Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Internal Medicine, 180(11):1491-1499, 2020.
- 2.
Liu D, Huang Y, Huang C, et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. The New England Journal of Medicine, 386(16):1495-1504, 2022.
- 3.
Cienfuegos S, Gabel K, Kalam F, et al. Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health in Adults with Obesity. Cell Metabolism, 32(3):366-378, 2020.