I haven’t written about intermittent fasting (IF) for over a year now and I still get questions about it from clients and in DMs almost every week.
I do have a previous post from 2019 that is a quick read if you’re interested, but in this article I’ll dive a little deeper into both daily short fasts and extended fasts and tell you what the current research says about both. I’ll also cover if I still do extended fasts or daily IF at the end.
Let’s dive in.
Types of Fasts
There’s differences between the proposed benefits of fasts depending on their length, so let’s define IF vs. Extended Fasts first.
IF = daily fasting, the most common structure being fasting for 16 hours and having an 8 hour feeding window (ex. eating meals between noon and 8 PM). However there’s other variations such as alternate day feeding and OMAD (one meal a day) eating.
Extended fasts = fasting for 24 hours or longer (obviously not done daily). 24 hours fasts are sometimes done weekly or monthly, 48-72 hour fasts are often done quarterly.
There’s a large group of people that should not do any kind of fasting and I’m not promoting any type of fasting. On a spectrum from encouraging it to discouraging it, I’m actually more on the side of discouraging fasting, especially for certain groups of people (like women and those with disordered eating tendencies). You shouldn’t feel bad or lesser if someone brags about how long they have gone without eating. Fasting can also be a convenient way to pass off disordered eating as something socially acceptable and even “healthy”.
Do your own research. Talk to your doctor. If you decide you want to incorporate some type of fasting into your life be smart and don’t start with a 72 hour fast. Start small and see how YOUR body reacts. Many people just don’t respond well, so listen to what your body’s response is.
Looking at meta analyses1,2 (research that looks at all the prior research on a topic) on intermittent fasting, the results suggest that, for weight loss, intermittent fasting could be beneficial. However, there’s not really any research to show that it is more effective than regular ol’ calorie restriction. So, if your goal is weight loss and eating your meals in a smaller time window helps you adhere, go for it. If eating in a smaller window makes you hungrier and obsess about food more, know that you are not any worse off simply creating a calorie deficit regardless of meal time.
This quote from the conclusion from the cited research really seems to sum things up, “Both intermittent and continuous energy restriction achieved a comparable effect in promoting weight-loss and metabolic improvements.”3
As for general health and prolonged life benefits, there is some animal research that may support this in mice or rats who have been given an IF diet or alternate day feeding for all of their lives4. More research is needed on humans to see if calorie restriction, IF or IF with restricted calories would produce similar effects.
TLDR: there may be modest overall health benefits to IF, we need more research on humans. For weight loss, both IF and calorie restriction regardless of meal time are effective.
As I go to write this section I almost don’t want to touch it with a ten foot pole.
This is honestly a confusing and relatively new field of research. Listen to podcasts with Dr. Rhonda Patrick, Dr. Satchin Panda or Dr. Valter Longo if you want more information and a deep dive into current human clinical trials that are being run.
Majority of this research has been done on mice and rats5,6. Saying that doesn’t dismiss the research, but it means we need to take that into account when extrapolating it to humans.
If you look at some studies, on mice and (the few) on humans, you could certainly be convinced of the “powers” of autophagy (the body getting rid of dead/dysfunctional cells) and it’s ability to improve the body’s overall health and longevity. This is initially what got me interested in prolonged fasting.
However, prolonged fasting is a stress on the body so if you are someone with a high cortisol level or unmanaged stress — prolonged fasting is likely not another stress you want to put on the body.
Although autophagy seems like an amazing process to “rev up” in the body, we just don’t know everything about it. Also coffee, saunas, sleep and exercise promote autophagy and you don’t have to give up food for 2+ days to get those benefits.
So is it worth it to do a prolonged fast to the health benefits related to autophagy? Maybe. We just don’t know for certain yet. But it may look like autophagy really picks up after 48 hours of no food.7
If you’re interested in more information on the 24 hour, 48 and 72 hour fasts I’ve done use the search feature on my website and read below about why I no longer do them.
Do I Currently Fast?
Short answer? No. Did I used to? Yes.
Why not? I’m not convinced theirs enough research on humans to show a benefit and I just haven’t felt like it.
I eat breakfast when I get hungry in the morning, which is usually 10-11 AM. I finish eating at about 7-8 PM. Some people might call this IF because I often eat in a 9 hour window. Really, I’m just listening to my hunger cues and what works with my schedule so I don’t really feel the need to call it intermittent fasting or feel like it is.
I also don’t purposely fast because there’s a chance that it conflicts with my goals of building and maintaining muscle mass by impairing my workout recovery.
There’s also a chance that fasting could negative impacts women’s hormonal health8.
I also feel like it’s a little silly to define ourselves by how or when we eat. I’ve enjoyed the challenge of a 72 hour fast in the past, but know I’m not sure challenging myself by withstanding from food is the right decision.
That’s where I’m at. What do you think about fasting?
Random food for thought that didn’t fit in elsewhere: Everyone essentially has an “eating window” and “fasting window” whether or not we think about it or define it. Does it seem likely that extending that window an hour or two could have that large of an impact on your body?