What Is 16/8 Intermittent Fasting?
The 16/8 method means you fast for 16 consecutive hours and eat all your meals within an 8-hour window. If you eat your first meal at noon and your last at 8pm, you're doing 16/8 — most of the fast happens while you sleep.
It's currently the most popular form of intermittent fasting because it fits naturally into most lifestyles. You're essentially skipping breakfast and eating lunch and dinner as normal. No counting calories (though it helps), no special foods — just a compressed eating schedule.
How 16/8 Works for Weight Loss
There are two main mechanisms:
1. Calorie Restriction (Primary Driver)
Compressing your eating to 8 hours naturally reduces how much you eat. Most people consume 200–500 fewer calories per day on 16/8 without trying — simply because there's less time to eat. This calorie deficit is what drives fat loss. See our guide on calorie deficit for weight loss for more on how this works.
2. Metabolic Switching (Secondary Driver)
After ~12 hours of fasting, your liver's glycogen stores run low and your body shifts to burning fat for fuel — a state called metabolic switching. This increases fat oxidation, though the effect is modest compared to the calorie deficit effect.
A 2022 NEJM review found that 16/8 produced similar weight loss to continuous calorie restriction when calories were matched — confirming that the timing itself isn't magic, but the structure helps most people eat less.
| 16/8 vs Standard Calorie Counting | 16/8 IF | Daily Calorie Deficit |
|---|---|---|
| Average weekly weight loss | 0.5–0.8 kg | 0.4–0.7 kg |
| Muscle preservation | Good (if protein is high) | Good (if protein is high) |
| Hunger management | Better for some | Harder for others |
| Dietary flexibility | Higher — no food rules | Lower — must track everything |
| Compliance at 12 months | Higher in studies | Lower in studies |
Best 16/8 Schedules
Pick whichever eating window fits your life. The best schedule is the one you'll stick to:
Common 16/8 Windows
What to Eat in Your Eating Window
16/8 has no food rules, but what you eat during your window determines how much fat you lose and how much muscle you keep. The non-negotiable is protein.
Aim for at least 1.6g of protein per kg of bodyweight per day. This preserves muscle during the fast and keeps you fuller longer. Check our protein per day guide for your exact target.
| Priority | Food Group | Examples | Why |
|---|---|---|---|
| 🥇 High | Protein | Eggs, chicken, fish, Greek yogurt, cottage cheese, tofu | Preserves muscle, highest satiety |
| 🥈 High | Vegetables | Spinach, broccoli, peppers, zucchini, cucumber | Volume without calories, fiber |
| 🥉 Medium | Complex carbs | Oats, sweet potato, brown rice, legumes | Energy, fiber, micronutrients |
| ✅ Include | Healthy fats | Avocado, olive oil, nuts, fatty fish | Satiety, hormones |
| ⚠️ Limit | Ultra-processed | Chips, cookies, fast food, sugary drinks | High calorie density, low satiety |
Sample 7-Day 16/8 Meal Plan (12pm–8pm window)
~1,600–1,800 kcal/day, 120–140g protein. Adjust portions to your calorie target — use our calorie calculator to find yours.
| Day | Meal 1 (12pm) | Snack (3–4pm) | Meal 2 (7pm) |
|---|---|---|---|
| Monday | 3-egg omelette + spinach + feta | Greek yogurt + berries | Grilled chicken + roasted broccoli + brown rice |
| Tuesday | Tuna salad wrap (whole wheat) | Apple + 20g almonds | Salmon + steamed asparagus + sweet potato |
| Wednesday | Cottage cheese bowl + cucumber + tomato | Protein shake | Ground turkey stir-fry with bell peppers and rice |
| Thursday | Chicken & avocado salad | Hard-boiled egg + carrot sticks | Baked cod + green beans + quinoa |
| Friday | High-protein overnight oats (made dry, eaten at noon) | Edamame | Lean beef + roasted vegetables |
| Saturday | Egg white scramble + sourdough toast | Cottage cheese | Shrimp stir-fry + brown rice + bok choy |
| Sunday | Smoothie: protein powder + banana + spinach + almond milk | Hummus + veggie sticks | Chicken thighs + roasted sweet potato + salad |
Side Effects & Who Should Avoid 16/8
Most people adapt within 1–2 weeks. Common early side effects:
- Hunger in the morning — usually passes after 5–7 days as ghrelin rhythms adjust.
- Headaches and fatigue — often from dehydration or low sodium. Drink water with a pinch of salt.
- Irritability — common in week 1. Plan easy, low-stress days when starting.
- Difficulty sleeping — some people find eating too close to bedtime disrupts sleep. Try a 10am–6pm window instead.
Who should avoid 16/8 or consult a doctor first:
- Pregnant or breastfeeding women
- People with type 1 diabetes or on insulin
- Anyone with a history of eating disorders
- Those who are underweight (BMI under 18.5)
- Children and teenagers
What Results to Expect from 16/8
Here's an honest, research-based timeline:
| Timeframe | What Typically Happens |
|---|---|
| Week 1 | 1–2 kg lost (mostly water weight from glycogen depletion). Hunger and adjustment symptoms peak. |
| Weeks 2–4 | True fat loss begins: 0.3–0.8 kg/week depending on calorie deficit. Energy stabilizes. |
| Month 2–3 | Visible body composition changes. 4–8 kg total fat loss possible with consistent effort. |
| 6+ months | Studies show continued fat loss comparable to continuous restriction, with better adherence for many people. |