Because I don’t believe in wasting anyone’s time, and I know a lot of you follow me for my no nonsense nutrition advice, I’m going to start with my bottom line up front!
You’re Welcome. : – )
We have a lot of great life to live and no one needs to spend endless time worrying about food or reading more than is necessary to get to the point.
The Bottom Line on Intermittent Fasting
There is not adequate evidence proving that intermittent fasting (any of the versions of it) has a long term and significant positive effect on health. There are opinions, theories and preliminary evidence for potential benefit, net neutral, and potential harm.
Any eating pattern that you decide to try out should be something you think you can sustain long term – maybe even for the rest of your life. For almost all of us … the conclusion on intermittent fasting is that it’s not worth the try.
Feel free to forget about this topic and keep your focus on getting those fruits, veggies, whole grains, beans and nuts and be sure you stop eating when you’re full!
However, there may be some common sense takeaways we can learn from the data.
What is Intermittent Fasting?
There are several different types of intermittent fasting
- Alternate day fasting
- Modified fasting
- Time-restricted fasting
Alternate day fasting– this is when you go whole days without consuming any food. Normally, the fasting days are spread out throughout the week.
Modified fasting– this type of fasting allows 20-25% of estimated calorie needs on the designating fasting day. This type of fasting is the idea behind the 5:2 diet (I covered that one here), where estimated calorie needs are met 5 days a week and 20-25% calorie needs are met 2 days a week.
Time-restricted fasting– this type of fasting is dependent on time. Food is restricted in intervals ranging from 12-20 hours.
What Does the Research Say?
The big question everyone seems to be asking is will fasting help lower risk of diseases and lower bio markers in the body?
Well, it’s conflicting…
Most of the studies that have been done on this topic have been done on rodents. I hate to break it to you, but there is a difference between human metabolism and rodent metabolism. If I read anything that cites an animal model for the study, I conclude that while the study might be interesting and can help guide future research, the findings are not necessarily applicable to my life. So I often just ignore it and move on.
What about research in humans?
There’s a 2015 review of data published here, if you like to read peer reviewed journal articles.
Their conclusions? [Bolded emphasis placed by me : – ) ]
“Clinical research studies of fasting with robust designs and high levels of clinical evidence are sparse in the literature. Whereas the few randomized controlled trials and observational clinical outcomes studies support the existence of a health benefit from fasting, substantial further research in humans is needed before the use of fasting as a health intervention can be recommended.”
Then in 2016, a study came out on prolonged nightly fasting and breast cancer prognosis – a retrospective study of women who “recalled” their behaviors.
“Fasting less than 13 hours per night was associated with an increase in the risk of breast cancer recurrence compared with fasting 13 or more hours per night. Nightly fasting less than 13 hours was not associated with a statistically significant higher risk of breast cancer mortality or a statistically significant higher risk of all-cause mortality.”
In other words – in this (not the strongest kind of study design) study, they found a CORRELATION between 13 hours fasting and breast cancer recurrence, but they did not see any increase in death from breast cancer or from anything else. As a reminder (A REALLY IMPORTANT REMINDER!!) about math and statistics, just because there is a correlation, does not mean that something caused something else.
I feel like there’s a lot of hype about not too much evidence.
What Should You Do?
I’m going to be honest. I had a really hard time writing this article. I slogged through information, rolling my eyes and wishing that it wasn’t so complicated to just find a simple answer. AND THIS IS MY EXPERTISE!!
I imagine that for many of my clients and followers, this information piled on top of all the other stuff is soooo overwhelming, it is enough to make you give up even caring at all. So again, I remind you that you are free to forget about this topic and keep your focus on the things we already know for sure!
However, I did mention that there are some common sense takeaways from this topic that we could all benefit from. So here’s what I figure:
- If you’re a cancer survivor and think that maybe you want to do some meal timing like what was reflected in the breast cancer study, a 13 hour window of “fasting” seems reasonable. Water, black coffee or unsweet tea counts as “fasting”. For some people, this is their natural window for finishing up dinner, going to sleep, getting up in the morning, enjoying coffee and then having breakfast.
- Some days we feast, some days we eat less and some days we eat a medium amount of food. That’s called normal eating, but some people have gotten away from that and feast every day. If an intermittent fast helps you bring awareness to your habits, maybe you would find benefit.
- Even with the “non fasting” days, in all of these studies, participants were encouraged to maintain a healthy lifestyle and make good, nutritious choices. It’s not like the “non fasting” times were full of processed foods and desserts all the time.
Also I should mention that if you are planning to do a more extreme version (the 16 hours a day fasting time, or fasting for entire days at a time), you should talk with your doctor and have some sort of medical supervision and guidance on the right way to do it.
Who should NOT attempt this?
- If you have diabetes, especially if you take medication for your diabetes, you should not do this. You should monitor your blood sugars and follow the recommended eating pattern and timing from your diabetes management team.
- If you have trouble getting enough to eat (people during treatment for cancer), or are having unintentional weight loss or problems with no, or little appetite, you should not do this. People who are struggling to meet their calorie and protein needs will need to focus on eating more often and frequently and should not go long periods without nourishment.
- If you have any history of eating disorders, disordered eating habits, yo yo dieting, emotional eating or restrictive eating behaviors (people who have tried all the popular diets that have come out), you should not do this. People in this group need to work their way towards intuitive eating habits and placing rigid guidelines on meal timing is not helpful.
- Serious athletes should not do this. Athletes are VERY dependent on getting adequate nourishment at the right time. This is not the right approach.
- People who don’t want to, should not do this. That’s me! : – )
If you should want more reading up on the topic, here are a few links that I found reasonable and easy to read.
- Quick coverage and dietitian quoted: http://www.chicagomag.com/city-life/July-2018/Meet-the-Chicago-Diet-Guru-Who-Studies-Not-Eating/
- Good review, very sciency and kinda long: https://sciencebasedmedicine.org/intermittent-fasting/
- Common sense approach: https://mesothelioma.net/intermittent-fasting-cancer-patients/
I hope this is helpful!