Temper your expectations when it comes to intermittent fasting. Much research has been conducted on animals, and it is more difficult to apply the findings to humans, who must deal with factors such as job stress, busy schedules, and food cravings, all of which can affect a person’s ability to stick to a specific diet.
1. 5:2 Fasting
Fasting days are any day of your choice.
The idea is that short periods of fasting keep you compliant; If you feel hungry on a fast day, you can look forward to the next day, when you can “feast” again.
“Some people say, ‘I can do everything for two days, but it’s too hard to cut back on what I eat for seven days,'” Kumar says. For these people, a 5:2 approach may be more effective than cutting calories throughout the week.
That said, try to avoid fasting on days when you do a lot of endurance exercise. If you’re preparing for a bike race or run (or running high-mileage weeks), evaluate whether this type of fast will work with your training plan or talk to a sports nutritionist.
2. Time-limited fasting
With this type of intermittent fasting, you choose an eating window each day, which should ideally leave a fasting period of 14 to 16 hours. Due to hormonal issues, Shemek recommends that women fast no more than 14 hours a day.
“Fasting promotes autophagy, the natural cellular maintenance process by which the body removes debris and other elements that hinder mitochondrial health, which begins when liver glycogen is depleted,” explains Shemek. This can 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 example. This can work especially well for someone whose family eats early dinner anyway, Kumar says. Then, a lot of the time spent fasting is time spent sleeping anyway.
Technically, you don’t have to “miss” meals, depending on when you set your window. But this requires consistency. If your schedule changes frequently, or you need or want the freedom to go out for breakfast every once in a while, go out for a late date, or go to happy hour, daily fasting periods may not be for you.
3. Full-day fast
In this intermittent fasting approach, you eat once a day. Some people choose to eat dinner and not eat again until dinner the next day, Shemek says.
With a full-day fast, the fasting periods are essentially 24 hours (dinner to dinner or lunch to lunch), whereas with a 5:2 diet, 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 all-day fasting, if done for weight loss, is that it is very difficult (but not impossible) to eat an entire day’s worth of calories in one sitting. The downside to this approach is that it’s difficult to get all the nutrients your body needs to function optimally with just one meal.
This approach can also be difficult to follow. You might be really hungry by the time dinner rolls around, which can lead you to consume not-so-good, high-calorie choices.
Think about it: when you’re hungry, you don’t really want broccoli. Many people also drink coffee in excess to satisfy their hunger, says Shemek, which can have negative effects on your ability to sleep. You may also notice brain fog throughout the day if you don’t eat.
4. Fast every other day
5. Choose your fasting day
This is more of a choose-your-own-adventure approach to intermittent fasting. You can do short-term fasts (e.g. fast for 16 hours, eat for 8 hours) every other day or once or twice a week, says Shemek.
For example, Sunday may be a normal eating day, where you stop eating at 8 p.m.; then you would start eating again on Monday lunchtime. Essentially, it’s like skipping breakfast a few days a week.
6. Fasting one meal a day
Some research also exists on “one-meal-a-day” fasting, which, as the name suggests, involves eating only one meal per day. But research into this method shows it could be more harmful than helpful.
Of note, the same study also found that for people who ate three meals a day, a maximum wait time of 4.5 hours between meals resulted in higher all-cause mortality. This means that researchers noticed that waiting longer between meals was linked to higher longevity rates.
