Temper your expectations when it comes to intermittent fasting. A lot of research has been done with animals, and it’s more difficult to apply the results to humans, who have to deal with things like work stress, crazy schedules, and food cravings, which can all affect one’s ability to stick with a specific diet.
1. 5:2 Fasting
With 5:2 fasting, you eat normally for five days, and don’t count calories. Then on the two other days, you eat between 500 and 800 calories, depending on your nutritional needs.
The fasting days are any days of your choosing.
The idea is that short bouts of fasting keep you compliant; should you be hungry on a fasting day, you can look forward to the next day, when you can “feast” again.
“Some people say, ‘I can do anything for two days, but it’s too much to cut back on what I eat all seven days,’” Kumar says. For those people, a 5:2 approach may work better than cutting calories for the entire week.
That said, try to avoid fasting on days when you may be doing a lot of endurance exercise. If you’re prepping for a bike or running race (or run high-mileage weeks), evaluate whether this type of fasting will work with your training plan, or talk with a sports nutritionist.
2. Time-Restricted Fasting
With this type of intermittent fasting, you choose an eating window every day, which should ideally leave a 14- to 16-hour fasting period. Due to hormonal concerns, Shemek recommends that women fast for no more than 14 hours daily.
“Fasting promotes autophagy, the natural ‘cellular housekeeping’ process where the body clears debris and other things that stand in the way of the health of mitochondria, which begins when liver glycogen is depleted,” Shemek says. Doing this may help maximize fat cell metabolism and optimize insulin function, she says.
With this approach, you set your eating window from 9 a.m. to 5 p.m., for instance. It can work especially well for someone with a family who eats an early dinner anyway, Kumar says. Then, much of the time spent fasting is time spent sleeping anyway.
You don’t technically have to “miss” any meals, depending on when you set your window. But this requires consistency. If your schedule is frequently changing, or you need or want the freedom to go out to breakfast occasionally, head out for a late date night, or go to happy hour, daily periods of fasting may not be for you.
3. Whole-Day Fasting
In this intermittent fasting approach, you eat once a day. Some people choose to eat dinner and then not eat again until the next day’s dinner, Shemek explains.
With whole-day fasting, the fasting periods are essentially 24 hours (dinner to dinner or lunch to lunch), whereas with 5:2 the fasting period is actually 36 hours. For example, you eat dinner on Sunday, then “fast” on Monday by eating 500 to 800 calories, and break it with breakfast on Tuesday.
The advantage of whole-day fasting, if done for weight loss, is that it’s really tough (though not impossible) to eat an entire day’s worth of calories in one sitting. The disadvantage of this approach is that it’s hard to get all the nutrients your body needs to function optimally with just one meal.
This approach can also be tough to stick with. You might get really hungry by the time dinner rolls around, and that can lead you to consume not-so-great, calorie-dense choices.
Think about it: When you’re ravenous, you’re not exactly craving broccoli. Many people also drink coffee in excess to get through their hunger, Shemek says, which can have negative effects on your ability to sleep. You may also notice brain fog throughout the day if you’re not eating.
4. Alternate-Day Fasting
This is a popular approach for weight loss. With alternate-day fasting (ADF), people might fast every other day, with a “fast” consisting of up to 25 percent of their calorie needs, and nonfasting days are normal eating days.
A study published in 2025 found that ADF more effectively reduced energy intake than time-restricted eating. This had a subsequent effect on body weight and fat mass. ADF also improved multiple cardiometabolic risk factors.
5. Choose-Your-Day Fasting
This is more of a choose-your-own-adventure approach to intermittent fasting. You might do the time-restricted fasting (fast for 16 hours, eat for 8, for instance) every other day or once or twice a week, Shemek says.
For example, Sunday might be a normal day of eating, where you stop eating by 8 p.m.; then you’d resume eating again on Monday at noon. Essentially, it’s like skipping breakfast a few days a week.
The research on the weight loss effect of skipping breakfast is mixed. There isn’t strong evidence to suggest that skipping breakfast affects weight. Some research has shown that eating a morning meal can modestly impact weight loss. And other research has linked breakfast skipping with an increased risk of mortality from cardiovascular disease, she says.
6. One-Meal-a-Day Fasting
Some research also exists on “one meal a day” fasting, which, as the name suggests, means eating only one meal per day. But research on this method shows that it might be more harmful than helpful.
Skipping breakfast, specifically, comes with a heightened chance of cardiovascular disease mortality, according to one study published in 2023. But skipping lunch or dinner also came with an increased risk of all-cause mortality.
It’s worth noting that the same study also found that for people who ate three meals per day, a maximum wait time of 4.5 hours between meals came with higher all-cause mortality. This means that researchers noticed that waiting longer between meals was linked with higher rates of longevity.
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