The simplest way to start intermittent fasting is to pick an eating window that fits your schedule, skip meals outside that window, and drink only zero-calorie beverages during fasting hours. Most beginners do well with a 14- to 16-hour overnight fast, which means finishing dinner by 7 or 8 p.m. and pushing your first meal to late morning. From there, you can adjust the timing, shorten the window, or try a different protocol entirely.
Choosing a Fasting Schedule
There are four main approaches, and the best one is whichever you can stick with consistently.
16:8 or 14:10 (daily time-restricted eating): You eat within a set window every day. A 16:8 schedule might mean eating only between 11 a.m. and 7 p.m. A 14:10 version gives you a wider window, say 9 a.m. to 7 p.m. This is the most popular method because it essentially just means skipping breakfast or eating an early dinner.
5:2 (twice-a-week calorie cap): You eat normally five days a week and limit yourself to about 500 calories on two non-consecutive days. On those low days, most people split the calories into a 200-calorie meal and a 300-calorie meal. You pick whatever two days work for you, as long as there’s a normal eating day between them.
Alternate-day fasting: Every other day, you either eat about 25% of your normal calories (roughly 500) or nothing at all. Non-fasting days are unrestricted. This is more aggressive and harder to maintain socially.
24-hour fasts (Eat Stop Eat): You fast completely for a full 24 hours, usually once or twice a week. Most people go breakfast to breakfast or lunch to lunch so they still eat something every calendar day.
If you’re new to fasting, start with 14:10 for a week or two, then tighten the window to 16:8 if it feels manageable. Jumping straight into 24-hour fasts or alternate-day fasting often leads to irritability, overeating during your window, and quitting.
What You Can Have During the Fast
The goal during fasting hours is to avoid triggering a significant insulin response. Water, black coffee, and plain tea are universally considered safe. Sparkling water is fine too. Adding cream, sugar, or honey to your coffee breaks the fast.
Artificial sweeteners are more nuanced than most fasting guides suggest. Research on drinks sweetened with sucralose or aspartame shows they don’t cause any acute rise in blood sugar or insulin over a two-hour period. So a diet soda or zero-calorie flavored water technically won’t break your fast in metabolic terms. That said, some people find that sweet flavors during fasting hours increase cravings, making the fast harder to sustain. If that’s you, stick with plain beverages.
When to Place Your Eating Window
Timing matters more than most people realize. Your body processes food more efficiently earlier in the day, when insulin sensitivity is higher and your digestive system is most active. An NIH-funded trial on time-restricted eating found that people who started eating at least one hour after waking and stopped at least three hours before sleep saw meaningful improvements: about 3% to 4% reductions in weight, BMI, and trunk fat, with an average loss of roughly 6.6 pounds. Importantly, that weight came primarily from fat rather than lean muscle.
The same study showed a modest but statistically significant improvement in hemoglobin A1C, a marker of long-term blood sugar control. This suggests that aligning your eating window with daylight hours, rather than eating late into the evening, amplifies the metabolic benefits of fasting. A practical schedule: eat between 10 a.m. and 6 p.m. rather than noon to 8 p.m.
Realistic Weight Loss Expectations
Intermittent fasting works for weight loss primarily because it reduces how much you eat. There’s no strong evidence that the fasting itself burns more fat than simply eating fewer calories would. A large Cochrane review comparing intermittent fasting to standard calorie-reduction diets found essentially no difference in weight loss between the two approaches, with the fasting group losing only about 0.33% more body weight on average.
Compared to doing nothing at all, intermittent fasting does produce results: roughly 3.4% of body weight over the study periods, which for a 200-pound person works out to about 7 pounds. That’s meaningful but modest. The real advantage of fasting over calorie counting is simplicity. Instead of tracking every meal, you follow one rule: eat during this window, don’t eat outside it. For many people, that’s easier to sustain long term.
Managing Side Effects
The first one to two weeks are the hardest. Common side effects include headaches, irritability, difficulty concentrating, and feeling lightheaded. Most of these fade as your body adjusts.
Headaches during fasting are often caused by dehydration or electrolyte shifts, not hunger. When you stop eating for extended periods, your body excretes more sodium and water. Drinking enough water is the obvious fix, but adding a pinch of salt to your water or drinking mineral water can help replace lost sodium. If you’re doing longer fasts (24 hours or more), consider an electrolyte supplement that includes sodium, potassium, and magnesium. Start with small amounts, around a teaspoon of an electrolyte powder mixed into water, and adjust based on how you feel.
Hunger tends to come in waves rather than building steadily. If you feel ravenous at 10 a.m. during a 16:8 fast, that sensation will typically pass within 20 to 30 minutes. Black coffee or sparkling water can blunt the wave. After a week or two, most people find their hunger signals naturally shift to align with their eating window.
Considerations for Women
Women’s hormonal responses to fasting appear somewhat different from men’s, though the research is still catching up. A study from the University of Illinois Chicago tested a strict four-hour eating window in both pre-menopausal and post-menopausal women over eight weeks. The good news: testosterone, androstenedione, and sex hormone-binding globulin (a protein that carries reproductive hormones) were all unchanged. The concern: DHEA, a hormone involved in ovarian function and egg quality, dropped by about 14% in both groups.
What this means practically is uncertain. A 14% drop in DHEA over eight weeks on a fairly extreme protocol (only four hours of eating per day) may not apply to more moderate schedules like 16:8. But if you’re actively trying to conceive or have a history of irregular periods, a gentler approach like 14:10 is a reasonable starting point. Pay attention to changes in your cycle length or symptoms, and adjust your fasting window if anything shifts noticeably.
A Note on Heart Health
A widely reported 2024 study of over 20,000 U.S. adults, presented at an American Heart Association conference, found that people who ate within an 8-hour window had a 91% higher risk of dying from cardiovascular disease over a follow-up period of up to 17 years. Among those with existing heart disease, eating within an 8- to 10-hour window was associated with a 66% higher risk of cardiovascular death.
These numbers sound alarming, but context matters. This was an observational study using dietary recall surveys, not a controlled trial. It cannot prove that time-restricted eating caused the deaths. People who eat in very narrow windows may have other risk factors, like shift work, disordered eating patterns, or medical conditions that led them to restrict eating in the first place. The study also didn’t capture what participants were eating, only when. Still, it’s a signal worth noting: restricting your eating to fewer than 8 hours a day has not been shown to extend lifespan, and the long-term cardiovascular effects remain genuinely unclear.
Who Should Be Cautious
Fasting is not safe for everyone. People with diabetes, particularly those on insulin or blood sugar-lowering medications, face real risks of dangerous blood sugar drops during extended fasts. If you take medications for blood pressure or heart disease, longer fasts can cause imbalances in sodium, potassium, and other minerals. People who need to take medications with food to avoid nausea or stomach irritation may find fasting incompatible with their treatment schedule.
Anyone with a history of eating disorders should approach fasting carefully. The rigid rules around when you can and cannot eat can reinforce restrictive patterns. Pregnant or breastfeeding women need consistent caloric intake and should not fast.
How to Start This Week
Pick a 14:10 window that fits your life. If you normally eat dinner at 7 p.m., that means your first meal is at 9 a.m. Do this for five to seven days. If it feels comfortable, narrow the window to 12 hours, then 10, then 8. There’s no need to rush to 16:8 or beyond.
During your eating window, eat the way you’d eat if you weren’t fasting: balanced meals with protein, vegetables, healthy fats, and fiber. Fasting doesn’t give you a free pass to eat poorly during your window. The research showing metabolic benefits involved people eating normal, healthy diets within their restricted hours.
Track how you feel, not just what the scale says. Improved energy, better sleep, and reduced afternoon crashes are common benefits people report within the first few weeks, often before any significant weight change shows up. If you’re consistently irritable, exhausted, or binge eating when your window opens, the schedule is too aggressive. Widen it, stabilize, and try again later.