Should you try Intermittent Fasting?
Holy smokes, there is a lot of information out there on fasting. Animal studies, human studies, time-restricted eating vs calorie restriction, long fasts, short fasts, women and men, athletes and Joe-the-plumbers, pros and cons… To dive into all of it today would be overly ambitious, and likely a bit overwhelming for most, so I think I will just start off the fasting series by covering the basics of intermittent fasting (IF) and the core physiology that supports most of the benefits found from it.
What is IF?
Intermittent fasting is a way of eating that involves periods of fasting between certain meals. It is an umbrella term for a variety of different types of fasts. For example, it can include: a 24-hour fast that has people eating only one meal a day followed by a 24-hour non-fasting period; a 16 hour fast where a person may eat dinner at 6 o’clock and then not eat until 10am the next morning; a calorie cycling type of fast that limits calories on certain days and not others; and a handful of others. Fasts are done for religious purposes, weight loss, metabolic restorative benefits, performance enhancement, and a variety of other reasons. The research continues to expand on this way of eating, finding a lot of application for folks that are interested in accelerating weight loss, improving metabolic markers, becoming more fat-adapted, and decreasing risk for some diseases like cancer and Alzheimer’s. I’ll get into some physiology around that later.
A Little Background
Fasting has been around for a LONG time, but it wasn’t always a choice. People were more or less forced to fast due to food shortages rather than purposes of disease prevention/treatment or performance enhancement. Some have even argued their brain cognition enhances and improves greatly with some fasting. We have been told that the template of three meals a day + two snacks a day is how we should eat in order to keep our metabolism going all day. This is a very big misconception. Our bodies do not want or need to stay in a fed state all 24 hours of the day. In fact, there are some very important functions our bodies prioritize that greatly benefit us when we are not constantly fed.
So, what are these functions and why do they help? Let me show you some of the effects of IF, then attempt to break down the physiology of fasting to help you understand how IF leads to these effects. I want to point out that IF is NOT for everyone. I will get to that more later, but please read through this whole thing before jumping on the IF train too quickly. There can be some rather big consequences for folks that try IF out without understanding why they are doing it and what it is doing to their body. Remember, fasting is a stress on the body. You need to be healthy enough to handle the stress in order to reap the benefits.
Intermittent Fasting Effects:
- Anti-aging properties
- Weight loss
- Increased Insulin sensitivity
- Increase in growth hormone, noradrenaline
- Fat-burning adaptation and ketone utilization efficiency
- Decrease in body fat
- Protect against diseases like Parkinson’s and Alzheimer’s
- Improve metabolic markers (cholesterol, blood pressure,
Alright, so let’s take a look at what happens to your body when you fast. To be clear, when I am referencing fasting, I mean not eating ANYTHING caloric for the given time. So, for the first 24-36 hours you used up your easily accessible glucose and have tapped into your glycogen stores. You started your fasted state about 12 hours post-meal, but are not entirely relying on ketones for fuel yet. After about 36 hours, you start tapping into some fat stores and begin to breakdown protein (I want to note that though this particular timeline notes protein breakdown now, you may still get some of these effects with a shorter fast too). There is a pretty large misconception that this is such a terrible thing for people, because OF COURSE you don’t want to breakdown protein in your body, right? All the hard work in the gym all gone to waste once you start fasting because your body begins to break it down? Well, it turns out that muscle is not the protein your body goes after first. Your body is breaking down other tissues that are ready to be cleared. Jason Fung, a [trainer? Doctor?], has noted that patients of his that lost significant amounts of weight through fasting did not end up with a lot of loose skin. The body actually broke down and utilized that would-be-loose-skin tissue for fuel in periods of fasting. Believe it or not, our bodies are SUPER good at finding cells that aren’t providing a lot of function and “cleaning house” by “eating itself”. This process is called autophagy. (You can learn more about this by reading/watching the Jason Fung interview referenced at the end of this post).
Autophagy- your body’s natural detoxification/cleanse
Much of the praises around fasting comes from the benefits of autophagy. Our cells are constantly turning over—breaking down, repairing, and regenerating. Though fixing cells is important, sometimes we have cells in our bodies that are just too far gone and need to be entirely replaced. We need to make room for new cells that can function more optimally. The damaged cells linger and can actually do quite a bit of harm to our bodies if they stick around for too long, like chronically releasing inflammatory cytokines (Wolf, 2015). Once they do die, they often die through a process called necrosis, which is the more dangerous and damaging clearing process in contrast to autophagy. With necrosis, the “kill” is uncontained and leaks chemicals that provoke inflammation and damage into the surrounding environment which can lead to more cellular damage and even cancer (Mizushima, 2008). I read a good analogy on cavemandoctor.com: “Autophagy is like pulling out a weed in your yard, while necrosis would be the equivalent of spraying your whole lawn with Roundup to kill that one weed.”
Autophagy slows down aging by ridding our cells of built-up clutter that causes aging, it suppresses cancer and tumor formation by blocking over-proliferation of cells (caveman) and can reduce development of neurodegenerative disease by turning over protein build-up in the brain. So, do you HAVE to fast in order to turn on autophagy and reap all these benefits? Well, no. You can turn it on by getting into ketosis, through exercise, or acute stress too. However, fasting has additional benefits beyond just autophagy that may have you considering it more.
Athletes and Fasting
There are special reasons, beyond autophagy, why athletes benefit from fasting. When you fast, your body becomes more fat-adapted. This means that you get better at using fat as fuel, and in turn, utilizing ketones as fuel. Ketones are byproducts of fat metabolism that can be used for energy. A lot of research these days has shown loads of benefits associated with ketosis—a state in which you are primarily using ketones for fuel because glucose is unavailable. This state can be very beneficial for athletes, especially endurance athletes. The more you can use ketones, the longer you can potentially go without hitting “the wall”. So, if a person is fasting, they are putting their body into a natural state of ketosis, thus training their body to utilize fat as fuel.
I would like to point out that everyone handles fasting and energy metabolism differently. This goes without saying, but it needs to be reiterated here. Different types of exercise require tapping into different energy systems, and some people are just wired to better use fat metabolism or glycolytic pathways more or less efficiently. If you have a curiosity with all of this, then you should practice your own experiment on yourself for a few weeks. It can take a while to adjust and adapt to working out while fasting, or working out in ketosis, and it may not be for you after weeks of trying and feeling drained during your workouts. There is no cut and dry prescription for fasting and athletes. There have been a lot of people that swear by it, and others that can’t handle it due to their body composition and/or underlying metabolic factors. In fact, lets’ talk about who should and shouldn’t attempt this lifestyle.
Should you start fasting?
For starters, I believe that first and foremost, a person needs to take a good hard look at their diet, sleep, and stress before attempting to implement intermittent fasting into their lifestyle. If you are eating a diet chalk full of refined carbohydrates, sugars, processed foods, industrial seed oils, and lacking nutrient dense whole foods, you are putting a lot of stress on your body to begin with and IF may help some, but definitely won’t be the fix to your problems. Additionally, if you are sleep-deprived and stressed out, IF will likely do my harm than good for you. You need to make sure you get those other components dialed in before making this intervention, otherwise you will likely not see the benefits and/or could seriously harm yourself. Other people that should proceed with caution:
- Underweight individuals
- Already lean people with low essential body fat stores
- People prone to eating disorders
- Women with adrenal fatigue or hormonal imbalances
- Those that are lean and looking to build muscle
If you fall into any of these categories, exercise A LOT of caution if you are considering IF. Feel free to reach out to me with questions if you want to still do IF. As mentioned before, there a lot of different ways people can fast, too, and depending on your training routine, you will definitely want to look into different options to find one most suitable for your lifestyle. I find time-restricted eating to be a great starting point. This is when a person doesn’t eat for 12-18 hours of the day, usually overnight, and only eats within an eight hour window of the day. I’ve seen and experienced some wonderful benefits from implementing this. Honestly, it feels great to not be so dependent on eating at certain times of the day or feeling dizzy, tired and famished if I haven’t eaten for just a few hours. I feel more in control of my intake, and less stressed out if I can’t eat for a period of time. Not to mention I have more stable energy and what feels to be less inflammation in my body. If you are curious to see if IF is right for you, I encourage you to do some research on the different kinds, or come see me and inquire about it. Like I said before, it is VERY important to check in to your current state of health before implementing IF. More to come on this topic in the near future where I dive into detail on fat-adaptation and ketosis and the effects of training while fasting!
As usual, please reach out to me for questions!
Therese Martinez, MS, RD, CPT
- Mizushima N, Levine B, Cuervo AM, et al: Autophagy fights disease through cellular self-digestion. Nature 451:1069-1075, 2008
- Mercola. 2016. The Complete Guide to Fasting: A Special Interview with Dr. Jason Fung http://articles.mercola.com/sites/articles/archive/2016/10/16/complete-guide-fasting.aspx
- High Intensity Health. Dec. 8, 2016. Jason Fung interview https://www.youtube.com/watch?v=v9Aw0P7GjHE
- The Paleo Solution Podcast with Robb Wolf. Dr. Rhonda Patrick Interview. 2015. https://robbwolf.com/2015/08/11/episode-282-dr-rhonda-patrick-cell-metabolism-and-other-geekery/
- Sisson, Mark. 2011. The Myriad Benefits of Intermittent Fasting. http://www.marksdailyapple.com/health-benefits-of-intermittent-fasting/#axzz1wmXsRd8K