NUTRITION SERIES: The Truth About Intermittent Fasting

Nutrition Series week 3 of 10! Today I'm going to discuss the truth about intermittent fasting. 

Trigger warning: if learning about a new diet could potentially trigger disordered eating behaviors, I would skip this blog post. 

I received this question from multiple people, and have been looking forward to it! My sophomore year of college we actually combed through all of the scientific literature of the best studies done on intermittent fasting, to come to the conclusion that I'm going to bring you with me to today. 

We know that intermittent fasting is a popular diet right now, and have been hearing mixed messages all around. I think it's important to take a deep dive into the specifics of its impact on our overall health and wellbeing, physically and psychologically. 

Let's start with what intermittent fasting is. 

Intermittent fasting can be done in multiple different ways - there's alternate day fasting, time-restricted feeding, whole-day fasting, and modified fasting methods (Wang et al., 2022). 

Alternate day fasting involves you consuming 25% of your daily caloric intake on your day of fasting, and then eating freely on your off day (Wang et al., 2022). 

Time-restricted feeding is when you fast during a specific allotted time during the day and eat freely the rest of the day, sometimes being 16 hours fasting and 8 hours of free eating, 18 hours fasting and 6 hours free eating, or 20 hours fasting and 4 hours free eating (Wang et al., 2022). Those who participate in Ramadan do a version of this type of fasting, for religious purposes. Disclaimer that I am not writing this post to discount anybody's religious values, I am discussing for those who do it for health purposes.

Modified fasting includes fasting on specific days of the week, with a few days a week of very limited caloric intake and a few days of free eating such as 5 days of eating 2 days of fasting, or 4 days of eating and 3 days of fasting (Wang et al., 2022).

Oftentimes the markers for "health benefits" include weight loss, lab values of LDL cholesterol ("bad" cholesterol), HDL cholesterol ("good" cholesterol), triglycerides, and blood glucose levels. So, that's where I am going to start. For context: we want to see HDL increase, and overall LDL, triglycerides, and blood glucose levels decrease. 

One review of 33 studies found that there was no impact of intermittent fasting on HDL levels (Meng H et al., 2020)

Another analysis of 33 studies found no impact on triglycerides, and LDL cholesterol; however,  LDL significantly increased in athletes and "healthy" subjects, and healthy was not defined.   (Mirmiran P. et al., 2019)

One specific study found that our resting energy expenditure, the calories we spend by doing absolutely nothing (making it an indicator of how well our metabolism is working) significantly decreased in females, and total energy expenditure, which includes physical activity, significantly decreased in males (Agagunduz et al., 2021). 

In short, this study concluded that intermittent fasting may lead to decreased energy expenditure - which is not good because long term, physical activity is what actually improves our HDL cholesterol, lowers LDL cholesterol, triglycerides and blood glucose levels and reduces risk of heart disease and diabetes (Centers for Disease Control and Prevention, 2021; Agagunduz et al., 2021; Kwon H.J. et al., 2017). 

Another review found that alternate day fasting resulted in weight loss, reductions in glucose and insulin in the bloodstream, in the 3 studies evaluating this method… but made sure to mention that it actually might not be practical, due to the fact that it leads to intense hunger on the days of fasting (Patterson R. et al., 2017).

You will certainly find studies that come back with conflicting results. There are studies with short term data showing improved oxidative stress, (oxidative stress is a risk for heart disease) - although, the studies used are measuring for 6 months or only a few weeks, and it also mentions, and I quote, "drawing comparisons between studies and extrapolating to broader populations may be perilous (Mohr et al., 2021)." Sheesh! Perilous is a strong word. That review says that there are limited findings supporting the POTENTIAL of intermittent fasting to make a difference in oxidative stress (Mohr et al., 2021). Limited in even supporting the potential. 

Another review found that intermittent fasting found a reduction in LDL for healthy participants… but not in "not healthy" participants, who, honestly, are generally the people we are trying to help reduce their LDL cholesterol (Meng H. et al., 2020).

Regardless of any positive outcome that is potentially found from this diet, to make any health outcomes valid, we need to see some long term data.

Where is the long term data? These studies are mainly weeks to months, and at most a year (Patterson R. et al., 2017; Torberg L., 2020). 

You can't extrapolate ANY information for long-term health in studies that last weeks-months with no long-term follow up. How do we know that it will help more than it will hurt? 

Our lab values fluctuate, being on a diet short term to see some improvement in lab values will not last forever, labs and symptoms that were supposedly improved in this very short window can easily be reversed (Wilhelmi de Toledo et al., 2020). It would be like cramming to study for a test the night before, and then doing okay on that test in the morning, and expecting that all studying is unnecessary moving forward ever again, that you will do fine on every exam you take in the future. 

Kind of like always cramming the night before exams, this type of diet is absolutely NOT sustainable long term (Trepanowski, J., 2017). It is, unfortunately, the fad diet of our age. 

If you're in it for these supposed very, very short term lab value improvements… let me share some short term impacts it can also have. 

Fasting is not what we were meant to do, our brain's activity is literally powered by glucose, and there is no getting around that - our brain needs food to stay alert and function properly (Wang et al., 2022). When we eat, glucose goes into our bloodstream, then gets metabolized in areas in our brain that perform specific tasks (Wang et al., 2022)! 

Not having enough glucose for our brain is like being at the end of your windshield wiper fluid, when it weakly sprays a little bit of fluid on but barely any and not enough to make much of a difference. It has a task it's supposed to accomplish and cannot because it simply does not have the resource it needs. Our brain's resource is glucose. If we fast, we run out of it. If we force our cars to fast from windshield wiper fluid, it's out of wiper fluid, it can't properly clean our windshields. And our brain's have much more important tasks than windshield cleaning. 

I'm not even going to start with the energy we need in order to consistently function physically or perform in athletics… if you are an athlete debating this diet, please just send me a DM. I mean, right now we're talking even allowing neurons to have the energy to fire in our brain so our brain can function, let alone exercising (Wang et al., 2022).

And let's not forget getting hangry! There comes anxiety and irritability, among many other negative emotions that can be consequent of low blood sugar and fasting (Wang et al., 2022).

The bottom line here is that there is not nearly enough research to come to any conclusions to support the use of this method (Mohr et al., 2021). However, since I'm me, I'm going to make you sit through the wider scope of this conversation, further disproving the prospect of this new trendy diet. 

We now walk into the realm of anti-diet Kyra (and now you're sorry you started reading but you can't stop because you're invested). 

We must consider the obsessive mindset it can put you in, of constantly thinking about food, the restrict-binge cycle that can happen when we restrict ourselves.

And off I go…

Diets don't work, they just don't. Our genes and brains protect us from them. Our weight has a set point, more so a set range, that we are genetically programmed to maintain (Harrison C., 2019). 

Our set range can actually be changed through dieting - as in, if we repeatedly try and force our bodies below its set range, it might end up increasing its range to protect us from future famines, i.e., diets (Harrison C., 2019). 

Up to ⅔ of weight loss attempts end up in more weight gain than what the original weight was (Harrison C., 2019). Our bodies increase or decrease energy output in order to maintain our set points, and if our weight drops below it, our brain senses it and kick starts biological changes to help us regain the weight and prevent the weight loss from happening again (Harrison C., 2019). Because it loves and cares about us! It does this by reducing our fullness hormone, increasing  our hunger hormone, lowering energy output, and reducing activity in parts of our bodies that regulate metabolism (Harrison C., 2019). 

When we restrict ourselves, our brain also increases the reward value we get from food and pushes us to eat more energy dense foods, and that reward value actually goes down in situations of food abundance… i.e., when we allow ourselves access to all foods at all times and honor our hunger (Harrison C., 2019).

These changes are the biological drivers of what Christy Harrison calls the "Restriction Pendulum" (Harrison C., 2019). It is our human natural reaction to deprivation. When it swings to restriction, there's going to be a swing back in the other direction because our bodies see it as dangerous (Harrison C., 2019). To our body, diets feel like famine. Even the most seemingly light diet pulls the pendulum to the side of restriction (Harrison C., 2019). When that happens, our body's natural response is to push the pendulum back to the other side - to eating a lot, feeling out of control with food, binging (Harrison C., 2019).

First we restrict, then we eat to the point of discomfort (often on foods we've forbidden ourselves from), then we think we don't have discipline or self control and we can't be trusted around certain foods, and we get mad at ourselves like it's our own lack of willpower (Harrison C., 2019). But it's actually physiological, literally a physiological reaction (Harrison C., 2019). We were not meant to do this. It's like shivering when we get cold, to survive (Harrison C., 2019). Our body wants to survive, so our bodies turn on food seeking signals forcing us to survive, because it is taking care of us (Harrison C., 2019).

A large scale study with more than 278,000 people found that within 5 years, 95-98% of those who were on diets for weight loss regained all of their lost weight (or more) (Harrison C., 2019). Intermittent fasting is in this category. Fasting is highly restrictive, and our bodies are meant to be nourished throughout the day… we were just discussing low blood sugar and our hungry mood swings! Our bodies and brains require consistent fuel. 

When we end up craving energy dense foods and binging we are not "addicted to food," this is a very appropriate physiologic response to restriction. 

This is no special new diet that will suddenly work. This new diet is no different from other restrictive diets - a study followed over 100 participants over a year with one group who did intermittent fasting, one who ate a normal diet, and one who did a typical calorie - restrictive diet, in which both groups who were on diets lost weight vs. the group who was not on a diet (Trepanowski J.F., 2017).

However, between the intermittent fasting group and the typical calorie restrictive group, there wasn't a difference in weight loss or any risk factors for heart disease; and actually, 38% of those doing intermittent fasting dropped out, driving home the point of how unsustainable fasting is, and it's not the only intermittent fasting study that's made the same point (Trepanowski J.F., 2017; Patterson 2017; Harris L. et al., 2018).           

It can also trigger even more disordered eating behaviors as we know can happen when we engage in short term disordered eating behaviors, and I would say it's not worth toying with.

Overall, weight is not our enemy… I want to go on and on about this part of the topic, but I will stop here today. 

We now know our body has its set point that we cannot change. We also know that intermittent fasting is not going to deliver on what we need long term. 

If you're reading this because you are on the diet, were considering the diet, or are trying to find a diet… take a moment to ask yourself why you are considering it. What were you hoping for it to solve? Based on your newfound knowledge of the topic, is this the solution to what you seek? 

It's always important to dig deep to find what we're looking for, because of how important we are, and we deserve the most nourished brains and fulfilled lives out there for us. We deserve true solutions. I'm always available for further discussion. 

References

Agagunduz, D., Acar-Tek, N., Bozkurt, O. (2021, December 18).  Effect of Intermittent Fasting (18/6) on Energy Expenditure, Nutritional Status, and Body Composition in Healthy Adults. Evidence-Based Complementary and Alternative Medicine. 2021, 1-10. https://doi.org/10.1155/2021/7809611

Centers for Disease Control and Prevention. (2021). Benefits of Physical Activity. https://www.cdc.gov/physicalactivity/basics/pa-health/index.htm#reducing-disease

Harrison, C. (2019). Anti-Diet: Reclaim Your Time, Money, Well-Being, and Happiness Through Intuitive Eating. Little, Brown Spark. 

Harris, L., Hamilton, S., Azevedo, L.B., Olajide, J., De Brun, C., Waller, G., Whittaker, V., Sharp, T., Lean, M., Hankey, C., Ells, L. (2018, February). Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database of Systematic Reviews and Implementation Reports. 16(2), 508-547.  10.11124/JBISRIR-2016-003248

Kwon, H.J., Lee, H.J. (2017, December). Effect of vigorous physical activity on blood lipid and glucose. Journal of Exercise Rehabilitation. 13(6), 653-658. 10.12965/jer.1735150.575

Meng H., 2020, Zhu, L., Kord-Varkenah, H., Santos, H.O., Tinsley, G.M., Fu, P. (2020, September).  Effects of intermittent fasting on and energy restricted diets on lipid profile: a systematic review and meta analysis. Nutrition. 77. https://doi.org/10.1016/j.nut.2020.110801

Mirmiran, P., Bahadoran, Z., Gaeini, Z., Moslehi, N., Azizi, F. (2019, September). Effects of Ramadan intermittent fasting on lipid and lipoprotein parameters: An updated meta-analysis. Nutrition, Metabolism and Cardiovascular Diseases. 29(9), 906-915. https://doi.org/10.1016/j.numecd.2019.05.056

Mohr, A.E., McEvoy, C., Sears, D.D., Arciero, P.J., Sweazea, K.L. (2021, December). Impact of intermittent fasting regimens on circulating markers of oxidative stress in overweight and obese humans: A systematic reveiw of randomized controlled trials. Advances in Redox Research. 3. https://doi.org/10.1016/j.arres.2021.100026

Patterson, R.E., Sears, D.D. (2017, August). Metabolic Effects of Intermittent Fasting. Annual Review of Nutrition. 37, 371-393. https://doi.org/10.1146/annurev-nutr-071816-064634

Torborg, L. (2020, March 10). Mayo Clinic Q and A: Long-term benefits and risks of intermittent fasting aren't yet known. Mayo Clinic. https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-long-term-benefits-and-risks-of-intermittent-fasting-arent-yet-known/

Trepanowski J.F., Kroeger, C.M., Barnosky, A., Klempel, M., Bhutani, S., Hoddy, K.K., Gabel, K., Freels, S., Rigdon, J., Rood, J., Ravussin, E., Varady, K.A. (2017, July). Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. Jama Internal Medicine. 177(7), 930-938. 10.1001/jamainternmed.2017.0936

Wang, Y., Wu, R. (January 5, 2022). The Effect of Fasting on Human Metabolism and Psychological Health. Dis Markers. 2022. 10.1155/2022/5653739

Wilhelmi de Toledo F., Grundler F., Sirtori C.R., Ruscica M. (2020). Unraveling the health effects of fasting: a long road from obesity treatment to healthy life span increase and improved cognition. Annals of Medicine. 52(5), 147-161. 10.1080/07853890.2020.1770849