A few months ago I heard about Intermittent Fasting (IF) from a good friend and respected colleague. It was something that piqued my interest and also made so much sense to me that I had to investigate further. I am very willing to try new things for health and weight loss as long as they are not detrimental to my health. I did have some health concerns about fasting; and the first things that came to my mind were probably the first things to come to your mind as well. 1. If I don’t eat then my metabolism will slow down and I’ll gain weight. 2. If I don’t eat then my body will use muscle as fuel and I’ll lose muscle mass. Before I dive into those questions, let me tell you a little about me and the lens I am looking at fasting through.
First of all, I am a husband and father of 2 boys. Secondly, I am a cardiac anesthesiologist. That means that pretty much every day I work all day in a physiology lab using drugs to manipulate heart rates, blood pressure, respiratory rates and level of consciousness. And on a day I am in the heart room, I use drugs to manipulate contractility (heart squeeze or function), preload (fullness of the heart), and afterload (work the heart has to pump against to eject blood). I measure those things in real time each heart beat using some very cool technology. Thirdly, I have fallen in love with cycling and am trying my best to become a stronger cyclist.
I decided to look closely into the above objections before I started fasting because I didn’t want to do anything to hurt myself. The first objection that I and others have to fasting is that “if I don’t eat then my metabolism will slow down and I’ll gain weight”. We’ve all heard this so much and for so long that we actually believe it’s true. In reality, there’s no way that it could be true. Even if your metabolism did slow down when you’re fasting (which there is good evidence that it doesn’t) you still have a basal metabolic rate (BMR). Your BMR is the amount of calories your body needs every day to keep your heart beating, keep you breathing, allow your brain to work, allow cellular repairs to be made, etc.. To basically keep you alive and upright. There are many, very complex formulas to calculate what your BMR is but it’s about 2000 kcal a day for a 6’0” 200 pound man and 1500 kcal for a 5’8” 165 pound woman. To make the math really simple, if you take in 0 calories and your body needs 2000 kcal every day to stay alive, there is no way you could gain weight. It is impossible!
The real response your body has to fasting is to actually increase your metabolism. This makes sense if you think about humans in terms of cavemen struggling to eat one meal a day, instead of modern people struggling to get their recommended (by many) 6 meals in a day. If you’re a caveperson and fasting because there is no food around, and if your metabolism slowed down so much you couldn’t get out and hunt or gather, you would simply wither and die. No more humans. No more hangry people missing their snickers bars. Your body actually secretes epinephrine and norepinephrine (adrenalin and noradrenalin) in response to fasting which revs up your metabolism to get you out there chasing that wildebeest down for dinner.
The second objection is that “my body will use muscle as fuel and I’ll lose muscle mass if I fast”. This was as important to me, especially as a cyclist. In general for cyclists the rule is the lighter you are the better a rider you are. It’s all about weight. We talk about a power to weight ratio which is actually how engine performance is measured. The more power you have and the less weight the better your performance and faster you will be. But there is a tipping point where you are so light you lose muscle and your power to weight ratio actually goes down despite your weight also going down. An example of this delicate balance is Nairo Quintana, a Columbian bike racer, winner of the Giro d’Italia, Vuelta a Espana, and twice second place finisher in the Tour de France. These are arguably the three hardest extreme endurance events in the world. He is 5’6” and 128 lbs. for a BMI of 20. That is the cutoff for being underweight. He is basically a hummingbird riding his bike up and down all those hills, and is right there on the edge of the power to weight ratio curve. I am not Nairo and want to lose weight but not at the expense of losing muscle, so I did some research into fasting and muscle loss. There was an article in the early 1980s called “Starvation” by Cahill. He looked at the excretion of urea nitrogen in the urine (a product of muscle breakdown) and found that it went down during fasting. The body is not burning muscle while fasting, it is preferentially saving it. Jason Fung, the guru of fasting and a hero of mine, put it very well: It would be like you chopped a bunch of firewood for the winter, and as soon as it snowed you threw your couch in the fire. Your body does not want to burn useful protein when there is plenty of fat around to burn.
So now that my mind was at ease and my two biggest concerns weren’t concerns anymore I felt like I could start my fasting experiment. During my experiment there were certain parameters that needed to be met. The most important were that I had to be able to safely provide care to my patients and that my bike riding must not suffer. The rest was up in the air, and so I began fasting.
This is my fasting journal, if you will, and how fasting has affected my life, my job, and my cycling. I hope you will check in on me and the progress of my experiment.
Jimmy Sederberg
Interesting
Looking forward to your story, but my elderly eyes are resenting the font. Would you please consider a friendlier print?
Will do for sure. Thanks for pointing that out to me