Metabolic Flexibility
– The Way of Your Body –

Dr. Al Danenberg Nutritional Periodontist

October 25, 2020 [printfriendly]

I write and lecture about diet. The nutrients we consume must come from nutrient-dense, anti-inflammatory foods. I connect the medical dots relating to our way of eating, gut health, and immune system strength. Everything I discuss about diet, nutrition, and the immune system is critical for health. But it all comes down to one basic concept – metabolic flexibility.

Paul Saladino, MD has recorded many videos and interviews about the importance of metabolic flexibility for overall metabolic health HERE. And Travis Christofferson published his latest book titled, Ketones: The Fourth Fuel, which explains the essence of metabolic flexibility.


Factors of Metabolic Flexibility

Metabolic flexibility is the ability for our body to use carbohydrates and fats for fuel from a healthy diet.[1],[2] Nothing more; nothing less.

But of course, there are other factors than the foods we eat that affect metabolic flexibility. Some of them are efficient exercise, restorative sleep, and reduction of overall stress. Also, the frequency of eating is a big player. Intermittent fasting as well as multiday fasting improve metabolic flexibility as long as the food that is ingested is nutritious with no addition of irritants or chemicals.

That being said, a widely reported medical study was published on 9/22/20, which made two summary statements that I believe are misleading. The study evaluated a group of overweight and obese participants who only ate between the window of noon to 8 PM for 12 weeks compared to a control group who ate three meals a day with no time window. The authors observed that participants who did intermittent fasting statistically did not experience significantly more weight loss compared to the control group. In addition, the investigators pointed out that those who practiced intermittent fasting had a loss of muscle mass compared to the control group. Unfortunately, there was an important caveat that was not emphasized in the abstract although it was reported at the end of the paper. The caveat was that participants did not eat a nutrient-dense, anti-inflammatory diet, which I have stated is critical for intermittent fasting to be effective and healthy. In my opinion, this limitation makes the publication not relevant.

Another important factor of metabolic flexibility is a diverse and abundant gut microbiome. This is required for healthy digestion, proper absorption of nutrients, a robust immune system, and an intact gut epithelial barrier.

With all these vital factors in mind, let’s take a look at our primal ancestors for a broader perspective.


Carbs & Fats

Throughout our modern human evolution over the last 200,000 years, our body has been effective in using both carbohydrates and fats for fuel. Our human machine has the hormones and chemical pathways to tell fat cells to release their fat storage when the body needs fuel and is not consuming carbohydrates. In addition, our human machine has the hormones and chemical pathways to burn consumed carbohydrates as fuel when dietary fats are not available.

When insulin levels are turned on with carb consumption, our fat cells are turned off from breaking down their stored fat. In addition, insulin converts excess carbs into fatty acids and stores them as fat. As blood glucose levels drop, we get hungry again.

Unfortunately, if we are used to consuming an abundance of carbs, our body does not resort to burning fats when we get hungry. Instead, we develop cravings for more carbs! We are not metabolic flexible. We are not “fat adapted”. We are “carb addicted”.

Why do we crave carbs when we get hungry? If we are “carb addicted”, our body yearns for more carbs because they stimulate dopamine production in the brain. Dopamine gives us a “rush”. If you refrain from carbs at this time, you will experience “withdrawal” symptoms just as you would if you tried to withdraw from other addictive substances. So, you just keep eating more processed carbs.

Even worse, when we consume an abundance of fats along with an abundance of processed carbohydrates, the body will not burn the excess fats. The end result is that fats and excess carbs are stored as more fat. Also, the liver is compromised with excess carbs coursing through the circulatory system. Excess carbs in the liver can cause non-alcoholic fatty liver disease.

A vicious cycle ensues, where fat and glucose cannot be metabolized effectively.

As time goes on, and we eat an abundance of carbohydrates several times a day, day after day, our metabolic hormones become strained. Problems with sleep, exercise, stress reduction, and gut health also will affect glucose metabolism.


Development of Diabetes

Insulin levels work hard to store the excess carbohydrates as fat. But if overeating continues, the effects of insulin become compromised. The cells in our muscles, body fat, and liver start resisting or ignoring the signal that insulin is trying to send out. That important signal is to grab glucose out of the bloodstream and put it into our cells. This is called insulin resistance.

The pancreas compensates by producing even more insulin in order to create the same results that it provided before the continuous overloading of carbs. In time, the pancreas can’t produce enough insulin and blood glucose can’t be directed into the cells. We become prediabetic. If the condition worsens, we become a true diabetic because glucose is not being metabolized effectively. Ultimately, the pancreas could weaken to the point of shutting down its production of insulin.


Steps to Become Metabolically Flexible

So, how do we become metabolically flexible? We must address our sleep habits, exercise routine, and ability to deal with stress. It’s also critical we become fat adapted by eating nutrient-dense, anti-inflammatory foods. In addition, we have to maintain a healthy gut. And finally, we should investigate the benefits of fasting.

To become metabolic flexible, our body needs to relearn how to burn fat as fuel. To do this, we must eat a diet that is extremely low in carbs for at least 2-3 weeks. Sometimes it might take several months before our body adapts. Eventually, our liver will start producing ketones as a clean burning fuel as our metabolism shifts into ketosis. Usually, this requires us to consume less than 30 grams of carbs a day. Think about this: one large apple has 30 grams of carbohydrate – your maximum allotment for that day!

An ideal way of eating is to primarily consume animal-based foods from nose-to-tail. These will provide the necessary source of nutrients contained in the animal muscle meat, organs, collagenous parts, and their healthy saturated fats. The fat-to-protein ratio in terms of grams should be 2:1. Eating fats and proteins are satiating and will curb hunger. Animal foods are extremely low in carbs. In addition, a few plants that are low in phytates, lectins, and oxalates could be included as long as the total carbs are less than 30 grams.

As I stated, this eating lifestyle will put the body into ketosis, where fatty acids are being mobilized from fat cells to be used as fuel for the body, and the liver in now producing ketones as an additional clean-burning fuel. This is the protocol I describe in my Better Belly Blueprint.

After your healthy metabolic flexibility has been reestablished, you can cycle in and out of burning fat and burning carbohydrates. To do this, you could reduce your fat consumption once a week and eat about 100-150 grams of carbohydrates that one day. Your body will burn the carbs for fuel and store some of it in the liver and muscle as glycogen. Also, the release of insulin at that time will assist your body in various repair pathways that are required. Over the following 6 days, you can go back to a high fat and low carb way of eating. Your protein levels will remain moderate. And you will stay metabolically flexible.


My Personal Metabolic Cycling

First of all, MCT (medium chain triglycerides) Oil acts as an exogenous ketone source. When a person consumes it and is eating low carbs, the liver will immediately convert MCT Oil into ketones. The rush of ketones into the blood system will cross the blood brain barrier and will benefit cognition and neural tissues since it is a perfect brain fuel. It also decreases overall free radical creation, improves the production of ATP by mitochondria, and enhances the natural production of endogenous antioxidants. Basically, it extends ketosis and improves energy.

Now for my personal metabolic cycling regimen. I am not recommending the following regimen to anyone. This is for information only.

I eat an animal-based diet, which includes less than 10% plants as I described previously. In my morning coffee, I add MCT Oil. Starting at 6 AM, I blend 2 tablespoons of ghee and 2 tablespoons of MCT Oil in 16 ounces of pressed coffee. And I’ll drink this over the next couple of hours.

My ketone levels stay high. Then I continue my animal-based diet with my first main meal sometime between 2PM and 5PM.

I will cycle out of ketosis every 7th day by increasing my carbs to 100-150 grams and significantly reducing my fats that day. I get my carbs primarily from raw manuka honey, some bee bread, and occasional fruits. On “carb” day, I do not drink any coffee. This protocol keeps me metabolically flexible and boosts my overall wellbeing.

Be aware of this: It was critical for me to titrate up to my daily dose of 2 tablespoons of ghee and 2 tablespoons of MCT Oil per day. I started with 1 teaspoon daily until I finally reached 2 tablespoons. If I had jumped in with a total of 2 tablespoons of both the first day, I would have experienced nausea, stomach distress, and diarrhea.

Concluding comment: Our DNA blueprint wants us to be metabolically flexible. This is the way our body is supposed to work. This was how humans have survived and thrived throughout our evolution over the last 200,000 years.

One way to determine your metabolic flexibility is to understand how your body metabolizes ingested carbohydrates by measuring your glycemic variability (GV). You can do this 24/7 by using a Continuous Glucose Monitor (CGM). I describe the details in my personal experiment. Read the facts and how you can get a CGM to monitor your own GV HERE.

My bottom-line recommendation is: Don’t fool with Mother Nature!






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  1. Hi Dr Al. I have read repeatedly from many sources in the keto/carnivore world that I should be aiming for approx 0.8 g protein per lb body weight to maintain bone density and lean muscle mass. My BMR is about 2500 calories and although I lift weights 4-5 week, at this point my goal is to lose fat.
    I see you recommend 2:1 fat/protein ratio. I find if i shoot for 0.8g/lb, theres no way i can do 2:1 without without ending up at 3500 calories, way over my BMR. I’m closer to 45/55% fat/protein.
    Am I missing something here? Thanks

    • Joe:
      Here is my calorie calculation for a person who weighs 150 pounds with 20% body fat.
      1 gram of protein = 4 calories; 1 gram of fat = 9 calories
      The general formula of protein to consume daily is 0.8 times the lean body mass in pounds.

      In this example, the lean body mass is 120 pounds (150 X .80 = 120).
      The grams of protein that this person should eat daily is approximately 96 grams (120 X .8 = 96), which equals 384 calories (96 X 4 = 384).
      If you eat 96 grams of protein, then your goal would be approximately 192 grams of fat (96 X 2 = 192), which equals 1728 calories (192 X 9 = 1728).
      The total calories would be 2,112 calories.

      Here is a link discussing percent body fat for men and women:

  2. Great article Dr. Danenberg. I first heard about you on Dr. Saladino’s podcast. You have a phenomenal story.

  3. What would your suggestions be for a 52 yo female diagnosed with PMR-GCA that does not want to take the prednisone regimen. Should she start with the prednisone while switching to a primal / carnivore diet? Thank you.

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