The simplest way to start fasting is to pick a daily eating window of eight hours, eat your meals within it, and consume nothing but water, black coffee, or plain tea for the remaining 16 hours. This 16:8 approach is the most studied and sustainable entry point, but several other methods work depending on your goals and lifestyle. What matters more than which protocol you choose is how you structure your eating window, what you drink during the fast, and how you break it.
Choosing a Fasting Method
Most people gravitate toward one of three approaches. The 16:8 method means eating during an eight-hour window and fasting for 16 hours each day. If you finish dinner at 7 p.m., your next meal would be at 11 a.m. This is the easiest to maintain long-term because it essentially means skipping breakfast or skipping a late dinner.
The 5:2 method takes a weekly approach instead of a daily one. You eat normally five days a week and limit yourself to one 500 to 600 calorie meal on the other two days. Those two low-calorie days shouldn’t be back to back. This works well for people who find daily fasting windows too restrictive or whose social lives make consistent meal timing difficult.
A third option is OMAD (one meal a day), where you compress your entire day’s intake into a single meal. This is significantly more demanding and harder to get adequate nutrition from, so it’s best treated as an occasional tool rather than a permanent lifestyle. A review of 40 studies found that intermittent fasting typically produces a loss of 7 to 11 pounds over 10 weeks, regardless of which specific method people used.
When You Eat Matters as Much as When You Don’t
Your body processes food differently depending on the time of day. Research comparing early eating windows (first meal between 6:30 and 10:30 a.m.) with late eating windows (first meal after 11:30 a.m.) consistently finds that eating earlier produces better metabolic results. People who ate earlier showed greater improvements in insulin resistance, with measurable reductions in how hard the body has to work to manage blood sugar. There was also a trend toward lower fasting glucose and modestly more weight loss, though those differences were smaller.
This means an eating window of, say, 8 a.m. to 4 p.m. is likely more beneficial than noon to 8 p.m., even though both are technically 16:8 fasts. If you can shift your eating earlier in the day, the evidence suggests you’ll get more out of the same fasting duration. That said, a later window you actually stick with beats an earlier one you abandon after a week.
What You Can Drink While Fasting
Water is always fine. Black coffee and unsweetened tea are generally considered acceptable because they contain negligible calories. However, caffeine does affect blood sugar regulation. About 200 milligrams of caffeine (one to two cups of brewed coffee) can temporarily reduce insulin sensitivity, meaning your body has to produce more insulin to manage the same amount of sugar. For most healthy people this effect is minor and doesn’t negate fasting benefits, but if you’re fasting specifically for blood sugar control, keep your coffee intake moderate.
Anything with calories, sweeteners, or cream will break your fast. Diet sodas are a gray area: they contain zero calories but some artificial sweeteners can trigger an insulin response in certain people. If you want to play it safe, stick to water, plain coffee, and plain tea.
Staying Hydrated and Avoiding Side Effects
The most common complaints during fasting are headaches, fatigue, irritability, and muscle cramps. These are almost always caused by dehydration or electrolyte imbalances, not hunger itself. When you’re not eating, you miss out on the water and minerals that food normally provides, so you need to compensate deliberately.
During fasting periods, aim for these daily electrolyte targets:
- Sodium: 1,500 to 2,300 mg. A pinch of salt in your water handles this.
- Potassium: 1,000 to 2,000 mg. Easily covered during your eating window with bananas, potatoes, or avocados.
- Magnesium: 300 to 400 mg. Nuts, dark chocolate, and leafy greens are good sources, or a simple supplement.
If you’re doing a standard 16:8 fast, you can get most of these through your meals. For longer fasts (24 hours or more), adding a small amount of salt and a magnesium supplement to your water becomes more important. Most people who say fasting made them feel terrible were simply under-hydrated.
How to Break Your Fast
For a daily 16:8 fast, breaking the fast doesn’t require much ceremony. A normal, balanced meal works fine. But if you’ve fasted for 24 hours or longer, your digestive system needs a gentler reintroduction.
Start with foods that are easy to digest and contain some protein and healthy fats. Eggs, avocado, and unsweetened yogurt or kefir are solid choices. Fermented foods are particularly well-tolerated because they support digestion. Avoid diving straight into greasy, high-sugar, or very high-fiber foods after a long fast. Raw vegetables, nuts, and seeds can cause bloating and discomfort when your gut hasn’t processed anything in a while.
Once you’ve eaten something gentle and given your body 30 to 60 minutes, you can move on to a full meal with whole grains, beans, vegetables, meat, or fish.
Adjustments for Women
Women’s hormonal cycles affect how the body responds to fasting stress. The week before your period is when your body is most sensitive to caloric restriction, and fasting during this phase can worsen PMS symptoms, disrupt sleep, and increase cortisol. Cleveland Clinic recommends avoiding fasting during the week before your period entirely.
Better times to fast are a day or two after your period begins and for about a week afterward. During the two weeks before your period is due (the luteal phase), either shorten your fasting window or skip fasting days altogether. Some women find that a 14:10 window works better than 16:8 throughout their cycle. If you notice your period becoming irregular after starting a fasting routine, that’s a clear signal to pull back.
Who Should Be Cautious
Fasting isn’t appropriate for everyone. People who are already at a low body weight risk losing too much, which can weaken bones, suppress immune function, and drain energy levels. If you have diabetes, skipping meals can cause dangerous blood sugar swings, especially if you’re on medication that lowers glucose.
People taking blood pressure or heart medications may be more prone to imbalances in sodium, potassium, and other minerals during extended fasts. And if any of your medications need to be taken with food to avoid nausea or stomach irritation, daily fasting windows may need to be designed around your medication schedule rather than the other way around.
A Practical Starting Plan
If you’ve never fasted before, don’t jump into a 20-hour fast on day one. Start with a 12:12 schedule for the first week: eat between 8 a.m. and 8 p.m., fast overnight. Most people already do something close to this naturally. During week two, push to 14:10 by delaying your first meal by an hour and finishing dinner an hour earlier. By week three, you can try a full 16:8 window and see how you feel.
Keep your meals nutrient-dense during eating windows. Fasting doesn’t cancel out poor food choices. The metabolic benefits, including improved insulin sensitivity (studies show meaningful reductions in insulin resistance markers), come from giving your body a consistent break from processing food, not from the fasting itself creating a caloric deficit. Some people lose weight with fasting, others don’t, and the difference almost always comes down to what and how much they eat when the window opens.