Flexibility is more than touching your toes, in fact, metabolic flexibility is even more important. The term metabolic flexibility refers to your cells’ ability to move between burning glucose for fuel to burning ketones derived from fat. This physiological capability is what allows our bodies to function and stay alive whether we have just been fed or whether we haven’t eaten for 24 hours or more. For the majority of human evolution, people were faced with times of feast or famine and without the metabolic flexibility to burn fuel from recently eaten food or fuel stored in liver, muscle and fat cells, the body would wither away and die between feedings. 

Feast and Famine 

Today, most people have access to plenty of food and rarely have to rely on the “famine” portion of metabolic flexibility. This state of being constantly fed is not necessarily good for us. Too much access to food leads to weight gain, inflammation, imbalanced microbiome, poor blood sugar control and chronic disease. It’s for these reasons that intermittent fasting or time restricted eating has become so popular. These habits give the body time to move into a state of “famine” and resort to burning stored glucose and fat instead of relying on glucose from a recently-eaten meal. In essence, these practices help our bodies mimic the feast-famine rhythm that the human body evolved to manage. 

Fueling Your Body 

When we eat carbs such as bread, pasta, corn chips, popcorn, rice, or sweets, our digestive system works fast to break those carbs down into little glucose molecules. From there, glucose is absorbed through the intestinal lining into the bloodstream. At this point, it is metabolic “go time” as glucose is shuttled to cells that need it for energy production. 

However, glucose can’t do this alone. Before glucose can enter your cells, insulin has to notify the cell that glucose is available. That’s the reason that when you eat glucose, your body triggers the pancreas to release insulin from pancreatic beta cells. Insulin also travels through the bloodstream where it’s delivered to cells and, like a puzzle piece, fits perfectly into healthy insulin receptors. 

When this process breaks down, whether due to a faulty pancreas or damaged insulin receptors, glucose metabolism slows down. 

It’s important to note that our cells only have two options for fuel: glucose and ketones. While we have been protein-obsessed for years, protein is not a fuel source. Protein has to be converted to glucose in a process called gluconeogenesis (gluco=glucose neo=new genesis=creation). This is the reason that eating too much protein can push someone out of ketosis. Protein can actually increase blood sugar by way of gluconeogenesis. 

Healthy metabolism relies on the ability to switch between glucose and ketones. Overfeeding, or eating too much too often, can cause poor glucose metabolism due to insulin resistance. This often occurs because overfeeding causes inflammation which leads to damage to insulin receptors on the cell surface. When this happens, cells can’t recognize insulin which prevents glucose from being taken up into the cells to metabolize for energy. 

This becomes a vicious cycle as glucose remains in the bloodstream, increasing blood sugar, and leading to more inflammation which leads to more insulin resistance, etc. Often this can go on for decades before eventually developing into diabetes. One of our primary goals when we work with patients is to identify and remedy this dysfunction well before it becomes a diagnosed disease. 

Boost Your Metabolic Flexibility

Just like stretching after a workout, you can improve your metabolic flexibility by challenging your cells to move between ketones and glucose for fuel. In essence, this means starving your cells of glucose in a systematic way so they can learn to depend on ketones as well. Depending on your current metabolic health, this may be challenging. People that really struggle to control blood sugar may benefit from a serious reduction of carbohydrates while healthier people can improve flexibility with fewer challenges.

Boosting flexibility does not happen overnight, and I many ways it takes a persistent curiosity to experiment and track your body’s response to these interventions. Tracking blood sugar levels is one of the most effective ways to assess how your body is managing fuel sources. I encourage you to use a glucometer to track blood glucose levels as you play with these tools for increasing flexibility.

We ask our patients to test their blood sugar upon waking, before each meal and one hour after each meal. A healthy blood glucose level is between 75-95 upon waking and before meals and between 80-100 an hour after eating. If your blood sugar is outside of those ranges, you may need support from a trained functional medicine provider.

You can experiment with these four tools at home to improve your metabolic flexibility 

1. Low-carb diet A low-carb diet only provides a small number of calories from carbohydrates. While this gives the body a little bit of glucose to work with, it doesn’t overburden the system with glucose which can prevent blood sugar spikes and improve insulin sensitivity and cellular metabolism. A healthy low-carb diet typically reduces/removes grains, sugar and legumes from your diet and focuses on high quality sources of nuts, seeds, low-carb veggies, berries, avocado, healthy oils, and small amounts of meat, eggs, fish, and poultry. 

2. Low-carb diet with high-carb feedings Another approach that can work well for people as long as they do not have uncontrolled insulin resistance is a rotation of low-carb or mild ketogenic days mixed in with one or two days a week that provide much higher amounts of carbs. This coaches the body into relying on ketones often and then pushes glucose into the body to prompt cells to burn glucose instead of ketones. In the right situation, this can really promote metabolic flexibility. 

3. Intermittent fasting Intermittent fasting (often confused with time restricted eating) is an approach that decreases caloric intake to around 600 calories 1-3 days a week. This creates a “fasted” state that mirrors a rhythm more like our ancestors may have experienced when they had days with little access to high-calorie foods but could nibble on wild plants. Again, this forces the body to stored energy, first burning through glucose stored as glycogen in the liver and muscle cells and then shifting to converting fat to ketones. 

4. Time restricted eating Time restricted eating (TRE) restricts eating to about 8 hours within a 24-hour period. Most people eat between 10am and 6pm and then give their bodies 16 hours to fast. While this can be problematic for people with poor blood sugar control and other complications like hormone or thyroid imbalance, for many people this is really effective for weight control and improved metabolic function. Studies have shown that even when people within an 8-hour period instead of a 12-16 hour period, metabolism and health improves without having to count calories. 

Takeaways 

Whether you are trying to lose weight, boost energy, improve health, reverse disease or promote longevity, metabolic flexibility is at the epicenter of these goals. Your body’s ability to produce energy is the foundation of cellular health and given that you are composed of trillions of cells, you need those cells to thrive if you want to experience your best health.

Just like an athlete would train for an athletic event, your cells need training to get the best results. Using the tools above, you can train your body into a state of optimal health by boosting metabolic flexibility. That said, food is more than fuel, it is also the delivery system for the countless micronutrients, phytochemicals, and antioxidants your body needs to function. While you’re boosting your metabolism by refining your macros, don’t forget that eating a diversity of whole foods is critical for ensuring that you are getting everything you need for your best health!