Intermittent fasting review: Comparing the popular IF programs
IF sounds very promising as a general ideology. But things get messy when it comes to actually doing IF.
How often should you fast? For how long? Should you eat zero calories? Should you eat the same amount of food on non-fasting days that you normally would, or should you eat more?
These are all questions that have no answers yet, so many IF proponents have come up with their own best guesses. Here’s a quick review.
Alternate day fasting (ADF)
36-hour fast/12-hour feed
With this plan you simply eat every other day. So on Monday, you’d eat within a 12-hour window, say, 8 AM to 8 PM. Then you’d fast overnight on Monday, and all day/overnight on Tuesday. You’d eat again from 8 AM to 8 PM on Wednesday. And so on. Alternate day fasters are encouraged to make good eating choices, but they’re allowed to eat what they want on the non-fasting days.
Some IF proponents believe we should behave like our evolutionary ancestors did. As humans evolved to get their food and exercise randomly, so should we. This brand of IF includes eating unprocessed “evolutionary friendly” food (think Paleo-diet type), randomly cycling daily calorie intake, and randomly skipping a breakfast or dinner meal once or twice a week. The rules are very flexible. (It is random, after all.)
Eat Stop Eat
24-hour fast, 1 or 2 times per week
On this plan, you fast for a full 24 hours once or twice per week, eating sensibly (higher protein, minimizing processed foods, etc.) the rest of the week. It’s flexible: You can choose whichever 24 hours you want. Want to fast from breakfast to breakfast? That’s cool. Just eat breakfast on Monday, and don’t eat again until breakfast on Tuesday. Want to fast dinner to dinner? That’s cool too. Eat dinner on Wednesday, and don’t eat again until dinner on Thursday.
16-hour fast/8-hour feed
This brand of fasting is based on an 8-hour feeding period followed by a 16-hour fast. However, it also layers a few other food rules on top. The diet should be high in protein, should cycle carbohydrates, should include fasted training, and should use nutrient timing (eating the bulk of your calories during the post-exercise period). On this plan, you fast from, say, 9 PM on Monday night until 1 PM on Tuesday afternoon. If you’re going to exercise, you’d do so just before 1 PM on Tuesday, with 10 g BCAAs (branched chain amino acids) during training. After training, you eat 2-3 meals before 9 PM, with your biggest meal coming right after exercise. The fast begins again on Tuesday evening until Wednesday at 1 PM, and repeats every day.
20-hour fast/4-hour feed
On this plan, you would either fast, or eat very small amounts of specifically recommended foods, for the first 20 hours of each day, working out during this period of under eating. Then, you would eat the majority of your daily intake within a 4-hour over feeding window. After that 4-hour over feeding period, you would repeat the under eating/fasting for the next 20 hours. Generally, most people place their 4-hour over feeding window at the end of the day, as it’s more convenient for family dinners and after-work training sessions. However, modifications can be made based on individual and scheduling differences.
As you think about these different IF variations, don’t focus too much on the differences between them. Instead, take a second and ask yourself what’s similar about each program. You’ll find they’re all variations on a single theme.
Theme and variations
Shrink the “eating window;” expand the “fasting window”
With most IF protocols, you simply draw out your normal overnight fast for a specified period of time – whether it’s 16, 24, or 36 hours. Likewise, you narrow your normal feeding window to 4, 8, or 12 hours.
Balance advantages and disadvantages
As mentioned earlier, some IF proponents believe that the longer the fast – up to but not over 36 hours – the greater the health and disease-prevention benefits.
However, longer fasts are a double-edged sword. Gaining – and preserving – lean mass is a critical part of healthy living and healthy aging, not to mention looking good and being fit. Unfortunately, longer fasts may harm muscle health and performance. They may also negatively affect nutrient intake: When you eat less of everything, you also eat fewer vitamins, minerals, and beneficial phytochemicals.
That’s why more physique- and fitness-conscious individuals tend to prefer shorter fasts (in the range of 15-20 hours per day) that end in a workout, followed by an eating period of 4-9 hours. Although it’s mostly speculation, there are two proposed benefits:
- The fasted workout can stimulate a physiological state similar to an extended fast.
- Eating most of your energy and nutrients in the post-exercise window can help with muscle recovery and nutrient partitioning.
Keep it real
Of course, there’s always the compliance challenge. Even if science were to show that one specific fasting plan is best, if you can’t actually do that protocol, you’ve got a problem. I suspect that’s another reason IF proponents suggest shorter fasts.
Doing a 24-36 hour fast once per week isn’t that big of a deal. Doing a 36-hour fast every other day? Well, that kinda sucks. Especially if you exercise regularly, which makes you hungrier and increases your calorie and nutrient needs.
On exercise and hunger
If you exercise regularly, you need more calories and nutrients than someone who doesn’t. Your body will ask for those nutrients by making you hungrier. IF protocols designed for non-exercisers will probably make you feel awful.
Of course, non-exercisers, beware of the same thing. Better yet, start exercising!
Because the research is so spotty, no one really knows which type of fasting is best for different goals – whether that’s fat loss, muscle preservation, disease prevention, or longevity. And because no one really knows whether IF offers any additional physiological benefits at all, everyone is just guessing. That’s not a problem as long as there’s sane self-experimentation involved.
As the various IF communities and early adopters test out their different ideas, the best ones will rise to the top. Eventually, scientists will catch wind of these and put them to the test. Right now, I’d say we’re a good 5-7 years from knowing what exactly IF does in humans (and why), and a good 10-12 years from knowing which IF protocols are “best.”
But don’t use this delay as an excuse for not making changes in your life. As the old proverb says, the man who deliberates fully before taking a step will spend his entire life on one leg.
Forget what science hasn’t yet proven. Establish best practices in your own exercise and nutrition habits, right now. Then once you have that experience to rely upon, you can tweak away to your heart’s content.
Let’s get started with the experiments.