In Pursuit of Metabolic Flexibility

Origins of the Pursuit for Metabolic Flexibility

There was a time when I was a big advocate of ‘grazing’.  Everything I was taught growing up emphasized this.  Breakfast is the most important meal of the day.  When I began playing sports, it was crucial to be eating constant small meals in order to ‘maximize gains’.  I figured the people telling me this must know best, so I never really questioned it.  I experienced midday crashes for years without really thinking about this practice.  The fact that I got extremely ‘hangry’ any time I missed a meal or snack just seemed to reenforce that this practice must be correct.

Realizing there was a problem

Eventually, I didn’t workout as much and I started putting on extra weight.  I started looking for a quick fix to drop the weight.  I read about different diets and saw firsthand how many friends of mine seemed to just melt it off following a ketogenic diet.  Just about every one of those people found that this diet worked until you no longer strictly adhered to ‘Keto’ and then you would quickly put the weight back on.  Even worse, some of these people developed issues with being able to eat the foods that they did before adopting Keto.  Carbs and Gluten became issues for them.  This pretty much confirmed that Keto was not for me.  This eventually lead me to Intermittent Fasting or my preferred term for what I was doing… Time Restricted Feeding (TRF).

What I thought was the solution

TRF was initially very difficult for me.  The blood sugar rollercoaster that I had been on for years did not want me to get off.  Initially, I cut out late snacking and eventually breakfast.  I used Zero to track my fasts which helped gamify things.  Zero also turned out to be a wealth of information.  I kept up with and actively participated in the research being conducted by the Zero team.

Eventually, I worked up to following a strict 18:6 protocol every day except for Saturday and Sunday (almost anything went on the weekend). Occasionally, I’d alter one day a week to 16:8 to accommodate any meetings or events that I had scheduled. I chose the 18:6 protocol because around this same time, I was reading about the benefits of autophagy on someone my age.  Research showed that longer periods of fasting have a more profound impact on autophagy.  So I strived to do at least 18 hours of fasting and occasionally stretched to One Meal a Day (OMAD).    Around this time, I started measuring the impacts of my experiments in TRF using Levels and a breath-based ketone monitor.

Fueling the Human Machine

All of the research I had done into Keto, opened my eyes to the fact that the human body operates on two main fuel sources… fat oxidation and glucose oxidation.  Keto was so appealing to me initially, because why not use the thing to fuel my body (fat) that I was most interested in losing?  TRF started to have a profound impact on my blood sugar spikes, but I wasn’t satisfied with the level of ketosis that I was achieving.  How am I going to lose fat if I’m barely ever getting into a base level of ketosis?

Feast and Famine

This lack of ketosis, combined with the pursuit of ever more autophagy, eventually led me to adopting a 24+ hour fast at least once a month.  Research was starting to point to regular fasting having many positive benefits for the common diseases of aging.  This made sense to me.  The longer fasts definitely resulted in me losing weight, but DEXA Scan testing showed that much of that weight was muscle mass and not fat mass!  More research would eventually educate me why this was so.  My body wanted to be fueled by glucose and it would do whatever was necessary to make that happen.

General consensus is that the current abundance of over nutrition is a very recent phenomenon for humans.  Our hunter gatherer (and even more modern) ancestors likely spent much time in a ‘fasted’ state between meals.  Before the advent of grocery stores, it wasn’t so easy to constantly graze and any excess nutrition would likely either be consumed immediately or if possible saved for times of famine.  Maybe it’s not so much a coincidence that the issues that just about every one develops beyond a certain age might be related to this relatively recent change in our eating habits?  More in depth reading on how the body stores fat and how it powers processes in the absence/presence of glucose eventually led me to discover the concept of Metabolic Flexibility.

What is Metabolic Flexibility?

Metabolic Flexibility is the ability for your body to easily switch between burning glucose or fat for fuel.  Things like insulin resistance and the grazing that I used to advocate for destroy metabolic flexibility.  Unfortunately, insulin resistance is not something that you can easily monitor in real time.  If you have a high fasting glucose though, you are likely insulin resistant (and therefore metabolically inflexible).  If you are metabolically inflexible, your body will tend to prefer processes that it can go through in order to create glucose rather than start burning fat.  Due to this, the fat burning process won’t really get turned on.  You can also experience metabolic inflexibility if you stay in a state of ketosis and then have an influx of carbohydrates come into your diet.  The goal of Metabolic Flexibility is to be able to seamlessly switch between fuel sources based on what is currently available.

What’s even better?  Achieving Metabolic Flexibility appears to be one of the most effective things you can do to combat metabolic disease.  What is metabolic disease?  There is a growing body of evidence that this is the precursor to just about every one of the diseases of aging that plague our modern society.

Achieving Metabolic Flexibility

There are many ways that you can achieve metabolic flexibility.  They all involve having awareness of how your body uses glucose, paying attention to your diet, exercise, some form of TRF and appropriate recovery.  I’m going to discuss the approach that I have been taking in order to increase my metabolic flexibility.


I have a workout routine based on progressing every 7 days.  My workouts consist of bodyweight exercises that I can do anywhere.  When I’m home, I have additional equipment that allow me to increase the difficulty.

I used to do a version of this workout early in the morning, but have moved the bulk of strength training to immediately before I break my intermittent fast. The reason for this is due to a number of studies that have shown interesting things that occur to the AMPK and mTOR pathways while strength training in a fasted state. I can talk about this all day, but the basic gist is that training while fasted and then immediately breaking that fast with the right type of meal has been shown to have positive impacts on muscle preservation while fasting as well as fat loss and insulin sensitivity. Working out fasted also depletes muscle glycogen setting things up to replenish this when you do eat rather than moving it into other unwanted forms of storage.  When I first read these studies it sounded too good to be true, but I’ve verified the results in my own testing and the analysis from Levels also confirms these benefits for me.  Occasionally, I will break my fast first in order to prevent anything from becoming too routine.  


All of my research and monitoring has lead me to prioritize a whole food diet and I split up the month into ‘weeks of focus’.  The areas of focus include:

  • Strength
  • Insulin Sensitivity
  • Autophagy
  • Thyroid

For each week, I tailor my diet, supplements and TRF around the current area of focus.  Each day within the week gets tailored further based on the workout that I’m doing.  For the most part, I’m following a modified cyclical Keto diet, lower carbs and calories when I’m focusing on catabolism and higher carbs/calories when I want to be more anabolic.


I moved away from TRF with strict long periods of fasting.  Instead, I try to fast for a minimum of 13 hours every day, ramping things up when I’m in catabolic periods.  During Autophagy week, there’s usually at least one 24+ hour fast.  Again, the more complex schedule is to prevent anything from becoming routine.

Glucose Awareness

I’ve been using a combination of continuous glucose monitoring with Levels and blood tests from InsideTracker.  In an effort to level off spikes in blood sugar, I use several combinations of things that work for me based on monitoring with these devices.  Some of the things I use include: Apple Cider Vinegar, chromium (when favoring anabolism) or berberine (during catabolism) before meals.  During meals, I mix some glycine in my beverage to assist even more.


When focusing on recovery with regards to my approach to improving Metabolic Flexibility, the most important things are good quality sleep and keeping your thyroid in good health.  I plan on writing a post in the future on my journey to get good quality sleep.  Keeping your thyroid happy, basically boils down to carb refeeds and relaxing use of some supplements during ‘Thyroid week’.

Metabolic Flexibility Marathon

The journey to Metabolic Flexibility is definitely a marathon and not a sprint!  Even though I’ve made some progress, I still feel that I have some way to go.  Each time I retest, I see incremental improvements and I feel better than I have in years.  I’m constantly tweaking this program as I learn more and intend to update this post.  What are your thoughts? What are you doing differently?  If there is something that I glossed over that could use more information, let me know!


2 responses to “In Pursuit of Metabolic Flexibility”

  1. […] You might notice that my morning ritual doesn’t include breakfast. I used to be a big advocate of ‘grazing’, but over the last few years I’ve become a complete advocate of pursuing Metabolic Flexibility. […]

  2. […] into how to increase my overall healthspan.  It’s becoming increasingly clear, that ‘metabolic flexibility‘ is key. While many of the great diseases of the western world have genetic components, […]

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