A 24-hour fasting period is essentially what it sounds like: if your last meal is at 8pm on Monday, then you do not eat again (at all) until Tuesday at 8pm. This can be done 1 to 3 times per week; two being the most common iteration.
It’s impossible to talk about 24-Hour fasts without talking about Brad Pilon and his book “Eat-Stop-Eat”, which is the definitive book on this style of fasting. ESE has been around for several years, but Brad continues to publish updated versions with more science whenever he can. It’s a well-researched book that also happens to be well-written.
Brad was one of the first people talking about I.F., and his approach is one of “lifestyle, not diet.” Brad discussed much of this in an interview I did with him, which you can readhere.
The 24-hour fast works well for a number of reasons. Firstit is easily adaptable to any lifestyle, and it’s very hard to screw up. The only rule is don’t eat for 24 hours. As mentioned above, this is much easier than a 36 hour fast, especially for those new to it.
Secondly, like most methods of fasting, the abstinence from caloric intake for large periods of time is going to be a large part of the reason for success. For example, if you generally eat 2,000 calories every day, that’s 14,000 calories over the course of a week.
If you remove two of those days, you’re eating 4,000 calories less. Without any other changes to your lifestyle, you’d be on pace for over one pound of fat per week. Even if you compensate and eat a little more on the days you’re not fasting, you are still going to wind up with a fairly substantial caloric deficit. Add in some exercise, and it’s not hard to see consistent weight loss.
Caloric manipulation aside, this style of fasting works incredibly well because of the effect that fasting has on your overall hormonal environment. More specifically, when we talk about fasting, we’re really going to talk about two hormones: insulin and growth hormone.
With regard to insulin, it seems the less often you eat, the less often you raise insulin levels. This is not surprising, obviously. It’s even less surprising that this would lead to fat loss, since we know that chronically elevated insulin levels make it very difficult to lose fat.
Therefore, if you’re eating less often, you’re going to have fewer insulin issues—even if you’re eating the same foods in the same amounts. (This, is a pretty strong argument against the popular frequent feeding method of 5 to 6 meals per day.) However, while fasting and infrequent feeding helps to control insulin and keep it low, that’s not enough to stimulate fat loss…unless growth hormone is present.
If insulin AND growth hormone are both low, there isn’t a huge effect on fat loss. And so, while insulin management is important, growth hormone management is even more important. Which brings us to the very predictable point: The effect of fasting on growth hormone is incredibly important.
Your body releases GH pretty consistently, but research has shown increased secretion of growth hormone in three specific instances:
● During/immediately after sleep
● After exercise (as little as 10 minutes)
● During and immediately after a fast
Looking at these three things—all of which are thoroughly discussed in Pilon’s Eat-Stop-Eat—it’s not hard to come up with a “best of all worlds” scenario. If you produce a lot of GH while sleeping, and you produce it while fasting, then the obvious combination is to continue fasting after you wake, allowing for prolonged GH secretion. From there, exercise will allow for increased production in addition to your prolonged secretion.
Maximizes both the presence of GH and its effect
Overall, this maximizes both the presence of GH and its effect. In addition, the elevated GH in combination with the low insulin is a deadly one-two punch to your body fat.
Finally one of the main benefits of both this style of fasting and the book itself is the incredible flexibility of the program and the ease with which you can adapt it to your lifestyle—you can fast any day you like, and can move it around at will to suit your social life, which is important.
There aren’t many here. The main problem that clients of mine seem have here is that 24 hours seems like a long time to go without food; however, this is not unique to 24-hour fasting.
That said, there are some people who seem to have medical problems with abstaining from food for a significant length of time. In particular, people with low blood sugar seem to have an issue. If you are hypoglycemic, you may want to tread lightly.
The only other problem here would be for people who train on fast days and don’t want to miss out on post-workout nutrition. This can be alleviated by either moving your workout to the end of the fasting period, or simply scheduling your off days and fast days to coincide.
HOW (AND WHEN) TO USE 24-HOUR FASTS
This is a style of fasting I tend to use when I get very busy and have to train in the evenings. Also, I use this pretty much any day when I have to go out to a large social dinner and am not going to be watching my diet.
For example, if I am going out on a Friday night, I might make my least meal Thursday at 8pm. Then, at dinner Friday, I’ll get to eat a lot of food, perhaps enjoy dessert, and be fine, even if I go out after and eat again.
While this type of fasting is suitable for more than “damage control,” it works well for me in an occasional fashion. However, for many of my coaching clients, this is a sort of “every other day” approach that works well with them.
More than anything else, I frequently find myself referring people to Pilon’s book as a an IF primer, and a good resource for understanding a lot of the science behind why fasting works. Check out Brad’s site and book for more info.