Those of you who keep up with fitness may occasionally come across the term “intermittent fasting.” So what is it?
IF 1: Precise meal scheduling
For some, it makes sense to eat on a very specific schedule, leaving large blocks of time without a meal. 12-20 hours is quite common for this type of intermittent fasting. If one trains every day, this can be an ideal way to trim extra calories without eliminating the nutrients they need for a workout.
Examples: Alice eats all of her meals between 7am and 6pm, leaving a 13-hour window where she is fasting. Bob eats all of his meals between 7am and 1pm, skipping dinner in the process.
IF 2: Day-long fasting
For others, it makes more sense to take an entire day off from eating, resulting in 24-36 hours without a meal. While it seems like a frivolous change, if I were to fast two days per week, I’d reach my goal 4 weeks sooner.
Example: Carol eats dinner at 7pm on Monday and has her next meal at 7am Wednesday morning. This is a 36-hour fast. Dave eats breakfast at 6am Monday and has breakfast at 6am Tuesday -- a 24-hour fast.
Why do people fast this way?
Calorie restriction is implicit in all cases. With IF1, it simply makes a lot of sense for some people to restrict their intake to certain hours to reduce late-night snacking and ‘fourth meal’ shenanigans. Sometimes this can include skipping specific meals of the day.
Wait, is that it?
Calorie restriction is required, but with intermittent fasting it’s only half the story. For IF2, an entire day without eating can reduce one’s weekly calorie intake by quite a lot, leading to an extra half-pound or more lost for each day fasting. Certain groups of people find it easier to stick to, and more of those studied lost weight with intermittent fasting (65% vs 40%). Or as the WSJ says “Eating much less on some days and normally on others is as or more effective than reducing one's calories to between 1,200 and 1,500 calories daily, though continued research is needed, scientists say.” The current thinking is that in addition to helping eliminate the urge to snack, it puts additional stress on the body, causing the dieter to burn additional fat.
Intermittent fasting is as much bro science as it is real science. Like everything in the weight loss space, there’s some amount of gimmick involved. But unlike many methods/products/sekretz promoted, IF is used by a surprisingly large number of people, but not actively monetized. Which makes some amount of sense. After all, it would be hard to write a book about this. “Condense all of your eating into an 8-hour window every day and see increased weight loss if you already have a caloric deficit and exercise regularly.” End of book.
There are strong indicators that it works when used as a supplement to an already-successful diet and fitness routine. But I’d caution against trying to do too much, too different, too quickly. If you’re switching to a ketogenic diet and restricting your calories severely and starting a new exercise plan and taking supplements and intermittent fasting… Not only are you going to crash quickly, but your body will not lose weight as quickly as maintaining a steady pace of smaller changes. Start slowly and add new elements as you progress.