The connection between intermittent fasting (IF) and mental health is not quite that clear. Hence, I had a difficult time fitting this topic into Foods for Thought. Nonetheless, IF is quite a hot topic and has some potential to influence health in a number of ways.

Unfortunately, we don’t know much about how IF directly impacts mental health. However, more research is accumulating in recent years.

Someday, we just might use IF as one more tool in the toolbox of resources in one’s journey towards healthful changes. How this may or may not serve to help digestive concerns and mental well-being is still to be determined.

What is Fasting?

With roots dating back to ancient times, fasting is a practice of refraining from eating any food for an extended period of time. There are many of reasons why one might choose to practice a fasting regimen.

Whether for religious or spiritual practices or for intended healing purposes. One might practice fasting for anticipated health benefits and longevity. Or even for uncommon reasons including political causes such as peaceful protests and civil disobedience. Many reasons why someone chooses to practice fasting.

What About Intermittent Fasting?

Intermittent fasting (IF) is a term broadly used to describe a specified schedule of splitting waking hours between eating hours and non-eating hours.

There is no right or wrong way to practice IF. For example, people could restrict their “eating window” (time when all calories are consumed) to an 8-hour window or to a 4-hour window one to three days weekly.

There is no “best” regimen to practice IF that works for everyone. There are some things to first consider and different models that can be followed in a more informed manner. Over time people practicing IF should modify their regimen depending on how they feel during fasting and on the intended and achieved outcomes.

Brain Changes During Fasting

Some ways how IF might impact mental health are explained by the various changes in cellular processes and metabolism. Specifically, hormonal and other changes that occur within the brain and digestive tract, aka “the second brain”. 

Because much of the science on these topics are still in its early days, I take a more cursory look at the research here. Furthermore, most of the studies on IF and the effects on brain health are from animal studies. So we must take this research with a bit of caution and not simply apply these findings to humans.

In one rodent study, researchers found long-term caloric restriction resulted in a reduction in all organs except for the testicles (male mice) and the brain¹! This suggests there must be some sort of compensatory or protective role that the brain responds with in times of severe calorie restriction, or during periods of prolonged fasting.

Potential Benefits of Intermittent Fasting (IF)

Commonly purported benefits include: 

• Weight loss (improved metabolic regulation)
• Blood sugar regulation (improved insulin sensitivity)
• Immune health (reduced neuro-inflammation)
• Digestive health
• Delaying the normal aging processes (increased BDNF, autophagy)

How Can IF Help with Weight Loss and Blood Sugar Levels? 

One way IF can impact blood sugar levels and weight loss is by improving insulin sensitivity¹. Insulin sensitivity is a measure of how effective cell receptors respond to the presence of insulin. This hormone (insulin) is required for cells to permit blood sugar into the cells to provide energy. Think of insulin as an important regulator of glucose (blood sugar) metabolism.

When regularly exposed to higher levels of blood sugar from eating large portions of carbohydrate-containing foods, this can be problematic. It leads to reduced insulin sensitivity or a down-regulation of the number of insulin receptors available on the cells. This is more likely to occur from eating too many refined types of foods low in fiber.

For some, IF offers more flexibility towards dieting and weight loss. More common forms of dieting encourage chronic restriction of calories. This means daily food intake is limited to approximately 20-40% less than normal intake. Think, normal “dieting”.

IF offers a different, more varied approach towards dieting. A different approach towards reducing caloric intake. With IF, food intake is only restricted on certain days, while other days dietary intake is not changed.

Considering the limited research on the long-term effects, IF should not be recommended as a long-term solution to weight loss. Though it may prove helpful to some on their weight loss journey, particularly in the short-term.

What’s the Link Between Digestive Health, Immune Health, and IF?

Frankly, this link is not well understood. Despite the limited science here, there might be some theoretical insight to gain here moving forward with research.

The link between digestive health, immune health, and IF brings us right back to the importance of a balanced gut microbiome and preventing chronic inflammation. For more on the gut microbiome and the connection with immune system, check out this Harvard article linked here. Also, I dive into this link in Chapter 2 of Foods for Thought.

Reasons how IF impacts digestive health:

• Longer times between digestive processes (hormonal changes)
• Disruption of the “normal feeding cycle” – reduced supply of carbohydrate-containing foods that also serve as fuel to the gut bugs (may alter gut microbiome composition)^2-4
• **Altered/Improved gut microbiome → reduced inflammation = improved digestive and immune health

** Last point is theoretical, only limited animal studies suggest this as a possibility; need more clinical studies, with human subjects and for longer periods of time to back this claim.

What About Claims of Delaying the Aging Process?

Extended periods of time between normal digestion frees up time for other important biological processes. It allows more energy for repairing and healing from oxidative stress, cellular damage, and removal of a buildup of toxins.

One example of this repair is called autophagy. Autophagy is the body’s natural process of cleaning up cellular debris and waste in times of starvation or prolonged fasting. You can think of this process of autophagy as an “intracellular recycling system.”⁵

Autophagy just might be relevant when it comes to helping prevent certain diseases and delaying the normal aging process. In other words, this could be good for longevity and preventing or delaying the onset of common neurological disorders. Consider how common and troubling Alzheimer’s disease is.

Alzheimer’s disease is characterized by a build-up of abnormal proteins that wreak havoc on normal neurocognitive function. This cellular recycling system (autophagy) helps get rid of these problematic proteins.

Fasting is just one way that we can induce this cellular recycling system. Though there is still a lot to be learned about how helpful or not IF may be for this claim.

Reasons how autophagy may help delay aging process:

• Helps with detoxification
• Hormone balance (insulin resistance; increase growth hormone)
• Reduce chances or complications of Parkinson’s, Alzheimer’s, and other neurodegenerative diseases⁶

Potential Disadvantages or Harmful Effects of IF

First, caution! IF is not for everyone.

For some, practicing IF might be harmful. For others, the potential risks or disadvantages might outweigh potential benefits. So the bottom line is you should do some research and discuss this with your medical provider prior to starting any sort of IF regimen.

When not practiced in a safe and informed manner, fasting can have concerning effects. Some of these include

• Fatigue
• Hunger
• Weakness
• Dizziness
• Decreased alertness or trouble concentrating

Fasting is not indicated for the following populations: 

• Diabetes or prediabetes*
• Pregnant or breastfeeding
• Eating disorders (or those at risk for)
• Under 18 years old
• Underweight and/or trying to gain weight
• Recent organ transplantation
• Immunocompromised (impaired immune system) 

*Or should be closely monitored by a physician

Further, it’s not just these particular populations at higher risks. Anyone who takes an overly restrictive or rigid approach towards IF, could potentially lead to other problems.

I advise caution to anybody adopting a fasting regimen on a daily, or any overly restrictive, way. Restricting your food on a daily basis limits your intake of important vitamins and minerals. For some, this may open the door to other problems with food like developing unhealthy thought patterns or disordered eating.

Also, consider how prolonged periods of fasting (e.g. 24-48 hours) can increase levels of the stress hormone cortisol⁷. In some cases, increased cortisol levels may contribute to weight gain. So the role with fasting and weight loss is frankly not that clear.

Different Types of Fasting

• Alternate Day Fasting – alternates between eating days and water-only fasting days. Limited research suggests it can help with weight loss. But evidence is not conclusive and there are also reports of extreme hunger on this type of fasting. This suggests it’s unrealistic or unsustainable for many. 
• Modified Fasting Regimens – limit caloric intake to approximately 20-25% of estimated energy needs on fasting days (e.g. two days per week) and then eat normally on non-fasting days. 
• Time-Restricted Feeding –  limiting all intake of foods/calories to a reduced “eating window”, such as to a 4-8 hour time frame. For example, one might eat all their meals between 12pm-7pm. 
• Religious or Ramadan Fasting –  a month-long practice of IF (from sunrise to sunset) through the holy month of Ramadan to honor Islamic beliefs

Popular Approaches Toward IF

• 16:8 Model – requires all food intake to be restricted to an 8-hour window. Although this model may sound relatively simple, it may not be so easy for some to follow. It’s important to gradually work up to such periods of fasting. Simply avoiding foods for eight hours in the morning or for the last hours of being awake, may have unintended effects on sleep and mood.
• 5:2 Diet – Fast two days per week and “eat normally” the other five days. For some, this may encourage eating whatever foods without regard to ensuring an adequate intake of balanced food groups on the five non-fasting days. On fasting days, food intake is restricted to approximately 25% of normal caloric needs.
• Fasting-Mimicking Diet (FMD) – Models of fasting are becoming more flexible. In a 2017 study, Wei and colleagues followed a regimen where people restricted their food intake for five consecutive days — approximately 40% of their usual caloric intake — each month for three consecutive months⁸. Compared to those following a normal diet, this relatively permissive approach towards IF resulted in significant improvements in body weight, total body fat, blood pressure, and insulin-like growth factor-1.

My Favorite Things About IF

• It avoids rigid rules and no equipment or products needed. No right or wrong way to approach it. I enjoy the flexibility and freedom of this. 
• The science and potential health aspects of it are fascinating! Sometimes, personally, I like to experiment with my own body. This can be helpful to gain more insight alongside the research I do, reading peer-reviewed academic articles. 
• I like to mix it up! Whether it’s saving time, getting bored of usual food choices, intended metabolic flexibility, or occasionally, just some laziness.

Last words – Get Informed First!

Do your proper research before diving into intermittent fasting!

IF is not for everyone. Though it very well might be helpful for many people.

Before making any changes, make sure that your unique medical condition is taken into consideration by your medical provider.

Thanks for stopping by today!

– Jason

References:

1. Francis, N. Intermittent Fasting and Brain Health: Efficacy and Potential Mechanisms of Action. OBM Geriatrics. 2020; 4(2); doi:10.21926/obm.geriatr.2002121
2. Karakan T. Intermittent fasting and gut microbiota. Turk J Gastroenterol. 2019;30(12):1008. doi:10.5152/tjg.2019.101219
3. Thaiss CA, Zeevi D, Levy M, Zilberman-Schapira G, Suez J, Tengeler AC, Abramson L, Katz MN, Korem T, Zmora N, Kuperman Y, Biton I, Gilad S, Harmelin A, Shapiro H, Halpern Z, Segal E, Elinav E. Transkingdom control of microbiota diurnal oscillations promotes metabolic homeostasis. Cell. 2014 Oct 23;159(3):514-29. doi: 10.1016/j.cell.2014.09.048. Epub 2014 Oct 16. PMID: 25417104.
4. Li G, Xie C, Lu S, et al. Intermittent Fasting Promotes White Adipose Browning and Decreases Obesity by Shaping the Gut Microbiota [published correction appears in Cell Metab. 2017 Nov 7;26(5):801]. Cell Metab. 2017;26(4):672-685.e4. doi:10.1016/j.cmet.2017.08.019.
5. Kuma A, Mizushima N. Physiological role of autophagy as an intracellular recycling system: with an emphasis on nutrient metabolism. Semin Cell Dev Biol. 2010 Sep;21(7):683-90. doi: 10.1016/j.semcdb.2010.03.002. Epub 2010 Mar 17. PMID: 20223289.
6. Meng T, Lin S, Zhuang H, et al. Recent progress in the role of autophagy in neurological diseases. Cell Stress. 2019;3(5):141-161. Published 2019 Apr 29. doi:10.15698/cst2019.05.186
7. Mazurak N, Günther A, Grau FS, Muth ER, Pustovoyt M, Bischoff SC, Zipfel S, Enck P. Effects of a 48-h fast on heart rate variability and cortisol levels in healthy female subjects. Eur J Clin Nutr. 2013 Apr;67(4):401-6. doi: 10.1038/ejcn.2013.32. Epub 2013 Feb 13. PMID: 23403876.
8. Wei M et al. Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Science Translational Medicine. 2017, 9(377):1-25.