The concept of Metabolic Flexibility is so scientifically profound that you will be incredibly pissed that you didn’t think of it. I first heard about Metabolic Flexibility from Dr. Mike T Nelson, who literally wrote the book on the subject.

We were chatting about fitness, life, HRV, and supplement protocols and we happened to dig into my research at UT on eating frequency. Dr. Nelson gracefully went into his thoughts on the possible mechanism behind my findings and I honestly just started nodding, because

1) I was furious that I hadn’t come up with this Metabolic Flexibility theory (it was first coined by researchers Kelley and Mandarino out of the University of Pittsburgh in the 90s) and…

2) I was even more angry I had not heard of it before this happenstance meet up with Dr. Nelson.

I have studied metabolism and physiology sideways and backwards and had this hypothesis that increased eating frequency was really a cultural reaction to decreased insulin sensitivity, but the simplicity of the Metabolic Flexibility ideology gave these mechanisms and my hypotheses a united principle and framework.

So what is it?

Here are a few definitions:

“Metabolic Flexibility is the ability of a system (i.e., whole organism, organ, tissue, or cell) to adjust fuel oxidation to fuel availability.”
Galgani et al. 2008

“Metabolic Flexibility is the ability to switch back and forth between the two major energy substrates – glucose and fat – based on availability and need.”
J. Stanton

“Metabolic Flexibility enables you to (1) transition between fats and carbohydrates so you can burn more fat when you’re not exercising; and (2) use carbohydrates when you are exercising to fuel that activity and perform at a higher level.”
Dr. Mike T Nelson

Let’s hit what this means for the obesity and the chronic health catastrophe in our country first and then if you want more info and tools on how Metabolic Flexibility relates to performance you can click here, here, and here, or better yet buy Dr. Nelson’s book – here.

What is Metabolic Flexibility

What is the Metabolic Flexibility

Most of my research at The University of Texas at Austin is on eating frequency and how it relates to adiposity (fatness) and metabolic disease risk (diabetes and metabolic syndrome) in high risk youth populations.

What our and many other lab groups have found is that eating more frequently is positively related with caloric intake (if you eat more often, you eat more calories) but negatively related to BMI, Body Fat, and Visceral Adipose Tissue, and Glucose/Insulin indices – AKA eating more frequently seems to be protective against fatness and diabetes risk in the general population (youth and adults) despite the consumption of more calories. Hmmmm, a juxtaposition if you still subscribe to the calorie myth.

The full argument behind the failure of the calorie model for weight loss and/or health is not within the scope of this post, but if you believe calories are somehow the Holy Grail of health or weight loss, wake up. They matter, but not really and without quality everything goes to hell in a handbasket real fast.

This eating frequency conundrum flies in the face of the calorie model especially given that many of these findings have controls for physical activity. But before slapping on a global health message, we cannot forget one of the most a pivotal components of analyzing research – the study population. One of Gretchen Rubin’s secrets of adulthood is, “I’m more like other people, and less like other people, than I suppose.”

I need to give you some props and let you know that if you are reading this post you are not eating like the average college Freshmen or high risk Latino adolescent from inner city LA. You don’t devour flaming hot Cheetos and Dr. Pepper like it is your job, 25-40% of your diet is not added sugar, and you hopefully eat far more than 7 grams of dietary fiber. The average American’s diet is undeniably atrocious. Combine this with inactivity and the fact that 93% of our soil is devoid of nutrients and we have managed to build a hurricane of malnutrition, fatness, and chronic disease.

Meanwhile, the media screams that eating frequency is the easy fix and the best thing since sliced bread and that if you don’t eat every 3 hours you will…die. The most common recommendation is to eat 6 small meals per day, but this recommendation has little if any foundation in controlled weight loss experiments and despite what some diet gurus may say, increased eating frequency absolutely does not rev your metabolism (zilch). What it can do is help you control your blood sugar if you are eating shit food and have been for a while.

Flexible Dieting

Flexible Dieting

To bring things back to Metabolic Flexibility, if you are metabolically inflexible AKA you cannot run on fat very well in a fasted state (weight loss resistant) and you cannot dispose of a dump truck load of bagels without going into a coma on the couch (insulin resistant), you have a very small window of fat and glucose that you can function in without symptoms – a la small frequent meals. It’s the only way to keep these fatties or skinny fatties awake in class or at their desks. That might seem harsh, but the popularity of small frequent meals is likely our culture’s way of self-medicating an inability to adjust fuel oxidation to fuel availability.

If we take a step back evolutionarily, if you had to eat every three hours in order to survive you just wouldn’t have made it, thus we evolved the ability to utilize multiple fuel sources and the ability to switch between them based on availability. And it looks like we have shot that in the foot with a steady stream of processed cheap foods. Thus 2/3 of our country is overweight, and 1 in 2 minorities will likely develop diabetes in their lifetime.

Yet, this is why individualizing dietary protocols and experimenting/collecting data is so important. We cannot just slap random protocols and general recommendations on humans and hope for the best. Unless you are collecting data, you have no idea exactly how exactly will respond to a one of your beliefs. Very low carb diets, intermittent fasting, and small frequent meals are powerful tools and assessments that need to be tailored to the individual.

They can be really helpful for some, but for others who are not mentally or physically ready for dropping carb intake or skipping meals, it can be hell on Earth. Without the right support, it can lead to binging on all the donuts ever, a loss of lean body mass, and weight regain to further smushy status (they regained the weight but their body fat percentage actually went up from the yo-yo diet – this is fairly common). No bueno.

End game: we all want to be as Metabolically Flexible as possible. I’ll give you some guidelines for how to become Metabolically Flexible in an upcoming article. Most of our general population would benefit greatly from acting like they have diabetes and testing their sugars regularly and then working to keep themselves at a much more even keel with dare I say it, organic vegetables and high quality fat and protein sources and then when they are ready they can start delaying meals and assessing how they feel and what happens.

Most athletes need the ability to smash people, weights, and glucose in the face, as well as burn fat effortlessly when we they are sleeping so they wake up still jacked and somehow even more tan than when they went to bed. I know amazing, but the road there for all of us will likely look different depending on who we are and where we are on the road, so question and experiment with new approaches, collect data and assess how you feel and the results you are getting. Don’t just throw up a prayer of a 30 min Jog combined with Sour Patch Kids and hope that the Metabolic Flexibility gods will answer with washboard abs, because they won’t.

* Big thanks to Dr. Nelson. You are a scholar and a gentleman. Learn more about him at or

* Photo by Rabah Rahil Photography