The fat adapted diet will make you a superhero

Little child girl plays superhero.

It’s called fat adapted or metabolic efficiency, but what the he** does that even mean?

Well, I am glad you asked because that is exactly the same way that I felt. So, I decided to figure out what is the deal.

A couple of disclaimers here, I am just reporting what I have found and how I understand it. If you have more information please share it so we can all get smarter.

As I understand it, this concept is nothing new. In fact, the founding father is a Dr. Phil Maffetone who has been preaching a fat adapted diet for over thirty years. As you may expect, ditching the high carb diet in favor of good fats was not initially well received. But, as more information is becoming available more and more athletes are embracing the new way of thinking.

To start, fat burning sounds like a dream come true, at least from a fuelling stand point. For instance, at any given point the body carries around 2000 calories in glycogen ( carbohydrates) but over 80,000 calories in fat. It stands to reason, that if you are trying to go longer than having more calories ( fuel ) to burn is the way to go. Add to this that burning fat does not come with the highs and lows of sugar burning. Anyone familiar with an epic bonk knows that it is something to be avoided.

If you have been around endurance sports for awhile, then you know that the traditional thinking is that we should be fuelling predominately from carbohydrates. The body’s muscles burn glycogen and glycogen comes from carbohydrates. Make sense.

Except, it is not entirely true. The body’s muscles also burn fat. The caveat here is that fat is burned at low intensity and glycogen at high intensity, although to be fair we burn both sources at almost all intensities, just the ratio changes. So it is easy to understand why we want to have carbohydrates for races where we should be putting out nothing but high-intensity efforts.

For me, I get that. At least for shorter distances. But, for Ultras there are very few of us who can redline all day long. So, I naturally assumed that the longer the distance the more fat burned. Apparently, it is not that simple.

How fast/hard you run/bike during training teaches your body what source of energy it should use. Most ultra runners train above the anaerobic threshold, teaching our body to look for carbohydrates for energy. So even though you slow down for race day or even once a week for long runs, it is not enough.

Instead, we need to spend the vast majority of our training below our aerobic threshold ( more on that later ) teaching our body to adapt to fat burning.

How do you train your body to fat burning?

Two words. Exercise and Nutrition.

Exercise – As stated above there are two states your body operates in during exercise, anaerobic and aerobic. Aerobic burns fats and generally occurs when you are going easier, slow jog or even at a walking pace. Anaerobic burns carbs and is engaged during intense workouts, think sprints or hill climbs. Interesting to note though, how fast your heart is beating is a good indicator but not the only one, for instance, weight lifting is entirely anaerobic but you will rarely see the same type of heart rates as you will see on a hill climb. During weight lifting your body uses the available blood sugar and glycogen stores as an energy source to perform the exercise. The glucose from these energy stores are burnt to provide energy to the body. During this process, very little or no oxygen is used. Hence it falls under the anaerobic category.

Why is this important?

Because we want to train below the aerobic threshold, our most reliable measurement will be a heart rate monitor but it will not always be a true indicator. Also, knowing what type of workout you are performing will be key.

Nutrition – I am still getting my mind wrapped around the nutrition part. But, this is how I understand it. You have three macronutrients that make up the food we eat –  protein, carbohydrates, and fat. It seems like the easiest and cheapest source of calories is carbohydrates, plus our bodies love to fuel off of them. The bad side effects are carbohydrates are essentially sugar and causes your body to spike insulin and store fat. Which is the exact opposite of what we are trying to accomplish, we want to burn fat. By eating fewer carbs, note this is not a carb free diet, and more fats we can provide our bodies with fat to fuel without the insulin spikes. Make sense?

Again this is a super simplified explanation. There are tons of books based on this subject alone, I will add a few to the resources section of this post.

Sounds good, how do I train aerobically?

Heart rate. Yup, for endurance athletes heart rates are the surest way to monitor what zone we are training in.

Heart rate zone? Yes, it can get complicated real quick. But, we don’t need to worry about all the heart rate zones, instead, we only have to make sure we stay in one zone. The aerobic zone.

To calculate your maximum aerobic heart rate there are a lot of options, including the 220 formula. The one I am starting with is the Maffetone 180 formula. It seems the easiest. Basically, take 180 and subtract your age. For me, that is 134 beats per minute ( bpm). Now you can get all complicated and add or subtract numbers based on your fitness level and injury history. For me, the simpler is the best.

Once you know your maximum aerobic heart rate, then train under that.  Actually, that is too general, according to Maffetone train within 10 beats of your maximum aerobic heart rate.

Willing to be a Guniea Pig?

I am done racing ultras for the year, so thought that now is the time to see how this whole thing pans out. After reading the Primal Endurance book, I have decided to embrace an 8 week transition period to see if I can make my body become a more efficient fat burner. I will try to write another article on this in about a month to let you know how it goes.


For people that really know what they are talking about.


Primal Endurance – Mark Sisson

The Big Book of Endurance Training and Racing – Phil Maffetone

Metabolic Efficiency Training – Bob Seebohar

The Paleo Diet for Athletes – Loren Cordain & Joe Friel


Metabolic Efficiency: Becoming a Better-Butter-Burner – Sunny Blende

Metabolic Concepts in Returning to Running-Joe Uhan

Are Endurance Athletes More Susceptible to Getting Diabetes? – Alex Hutchinson


Speed Up by Slowing Down with Phil Maffetone on Trail Runner Nation

Carb Burning Vs Fat Burning with Sunny Blende on Trail Runner Nation

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