Intermittent fasting isn’t a single diet. It’s a collection of eating patterns that cycle between periods of fasting and eating, and there are at least six widely practiced versions. They range from a mild 12-hour overnight fast to a full 24-hour stretch without food. The right one for you depends on your schedule, your goals, and how your body handles longer gaps between meals.
Time-Restricted Eating (16:8, 14:10, and 12:12)
Time-restricted eating is the most popular category. You pick a window of hours each day for all your meals, then fast for the remaining hours. The three common variations are:
- 16:8: Fast for 16 hours, eat within an 8-hour window. A typical schedule is eating between 11 a.m. and 7 p.m.
- 14:10: Fast for 14 hours, eat within 10 hours. For example, eating between 9 a.m. and 7 p.m.
- 12:12: Fast for 12 hours, eat within 12 hours. This often just means finishing dinner by 7 p.m. and not eating again until 7 a.m.
The 16:8 method gets the most attention, but 14:10 and 12:12 are easier starting points if you’ve never fasted before. The shorter fasting windows still give your body a meaningful break from digestion overnight, and many people find they naturally eat fewer total calories when they stop snacking after dinner.
When you place your eating window matters, too. Your body processes food more efficiently earlier in the day. Glucose tolerance and the rate at which you burn dietary fat are both higher in the morning than in the evening. An evening meal produces higher blood sugar spikes than the same meal eaten at breakfast. Research on circadian rhythms suggests that shifting your eating window earlier, say 8 a.m. to 4 p.m. instead of noon to 8 p.m., may improve blood sugar control, blood lipids, and weight loss outcomes. Higher evening calorie intake has been linked to greater total daily calorie consumption and increased risk of metabolic problems.
The 5:2 Method
Instead of fasting every day, the 5:2 approach limits calories on just two days per week. On those two “fasting” days, women eat around 500 calories and men around 600. The other five days, you eat normally.
Spacing matters here. You should leave at least one normal eating day between each fasting day, and ideally two or three. So fasting on Monday and Thursday, for instance, works better than back-to-back days. This spacing prevents excessive hunger from building up and makes the plan more sustainable over weeks and months. The fasting days aren’t zero-calorie days, which makes them more manageable than full fasts, though they still require planning to keep meals satisfying at such a low calorie target.
Alternate-Day Fasting
This method alternates between normal eating days and modified fasting days. On fasting days, you limit intake to about 500 calories, roughly 25% of what you’d normally eat. On non-fasting days, you return to your regular diet. The rhythm is simple: one day on, one day off, repeating indefinitely.
Alternate-day fasting is more aggressive than 5:2 because you’re restricting calories three or four days per week instead of two. It tends to produce faster initial results, but many people find it harder to maintain socially and psychologically. Dinner plans, family meals, and work events don’t always align with a fasting schedule that changes daily.
The Warrior Diet (20:4)
The Warrior Diet compresses eating into a four-hour window, with 20 hours of minimal intake. During the long fasting period, you can eat small amounts of raw fruits and vegetables, but the bulk of your daily calories come from one large meal eaten at night.
This approach sits between standard time-restricted eating and full one-meal-a-day fasting. The small daytime snacks make the long fast more tolerable, but four hours is still a tight window to get adequate nutrition. People who try this method often struggle to eat enough protein, fiber, and micronutrients in a single sitting.
One Meal a Day (OMAD)
OMAD is one of the most extreme common methods: a 23-hour fast followed by a one-hour eating window (some versions allow two hours). You consume your entire day’s calories in that single meal.
The appeal is simplicity. No meal planning, no calorie counting, no decisions about what to eat for breakfast or lunch. But the practical challenges are real. Eating 1,800 to 2,500 calories in one sitting is physically uncomfortable for many people, and it’s difficult to meet all your nutritional needs in a single meal. OMAD is generally considered an advanced approach, not a starting point.
Eat Stop Eat (24-Hour Fasts)
This method involves one or two complete 24-hour fasts per week. You pick a meal and fast until the same meal the next day. If you finish dinner at 7 p.m. on Monday, you don’t eat again until 7 p.m. on Tuesday. The remaining five or six days, you eat normally.
Unlike the 5:2 method, Eat Stop Eat calls for zero calories during the fast, not a reduced amount. That makes it significantly harder, especially the first few times. Most people who use this approach build up to it gradually, starting with 16:8 or 5:2 before attempting a full day without food.
How They Compare for Weight Loss
All intermittent fasting methods produce weight loss primarily by reducing the total number of calories you eat. A large meta-analysis of randomized clinical trials found that both fasting-based approaches and traditional daily calorie restriction led to weight loss of 5.5 to 6.5 kilograms (about 12 to 14 pounds) over six months. At the six-month mark, fasting methods had a slight edge, with participants losing roughly one additional kilogram of body weight and about one additional kilogram of body fat compared to those on standard calorie-restricted diets.
That advantage disappears over longer time frames. When studies tracked participants beyond six months, there was no meaningful difference between fasting and daily calorie restriction for total weight lost. This suggests that the best method is whichever one you can actually stick with. A 16:8 schedule that fits your life will outperform a 5:2 plan you abandon after three weeks.
What You Can Have During Fasting Hours
Anything with calories technically breaks a fast. During your fasting window, the safe options are water, black coffee, and plain tea, all without sugar, milk, or cream. Supplements can be tricky: those containing maltodextrin, pectin, cane sugar, or fruit juice concentrate add enough calories to interrupt fasting. A basic multivitamin without sugar or fillers is generally fine. Bone broth, despite being marketed as a fasting-friendly option, does contain calories and will break a strict fast.
Who Should Be Cautious
Intermittent fasting isn’t appropriate for everyone. People with diabetes face real risks from skipping meals, particularly those on medications that lower blood sugar. If you take blood pressure or heart medications, longer fasting periods can disrupt your balance of sodium, potassium, and other electrolytes. People who need to take medications with food to avoid nausea or stomach irritation will find fasting schedules difficult to manage safely.
If you’re already at a low body weight, fasting can push you into territory that weakens bones, suppresses immune function, and drains energy. There’s also limited evidence on how fasting affects older adults specifically, so the further you are from the typical study participant (generally a middle-aged adult with overweight), the less confident anyone can be about the outcomes.