The Capacity to Switch Between Fuels Is Our Aim
a key aspect of metabolic fitness is the capacity to switch between fuels….this capacity may be lost in insulin resistance.” ~Sir Philip Randle
I liken metabolic flexibility to financial flexibility. You can burn through money in a few different ways; some ways are more efficient than others (credit cards being the easiest). Let’s discuss coins. You probably rarely use them because they are slow and messy, but they are nice to have in your car to feed the parking meters. Similarly, you probably rarely use cash, except for tipping the bellman when traveling or for buying produce at the farmers’ market. If you’re like me, you purchase nearly everything with your credit card (because you can get bonus airline miles, dispute charges, track charges, and it’s clean).
The cells of metabolically healthy people have a similar ability to use energy currency in different ways. An external signal, whether it’s eating a large meal or starving, will activate the most appropriate metabolic signaling network available to either store energy or burn it for fuel. The scientific term for this on-demand variability in communication is known as metabolic flexibility. But just as we prefer credit cards, the furnaces (muscle tissue) of metabolically flexible people prefer to burn fat.
Sir Philip Randle of Oxford University coined the term “metabolic flexibility” in 1963, when he discovered that vascular tissue could switch back and forth between lipid and carbohydrate metabolism.
However, Randle also noted that insulin resistance increases cellular fatty acid production, reducing the ability of cells to burn fat for fuel. Insulin-resistant tissues instead rely on glucose oxidation, which is slightly less efficient than burning fat and certainly more messy (lactic acid is produced as waist).
Think about metabolic flexibility as fiscal flexibility. Let’s say you wanted to take your spouse out for a nice dinner and planned to pay for it with a credit card. If you had no cash to pay the parking valet or the coat-check attendant, and if the restaurant didn’t take credit cards, your financial flexibility would be limited for that moment.
Similarly, a metabolic inflexibility occurs in people who are obese or have insulin resistance or diabetes. Increased levels of free fatty acids (FFAs) are characteristic of these conditions. People with these health risks also have high levels of glucose in their bloodstreams, which inhibit fat burning and increase fat gain, perpetuating the metabolic syndrome. Increased free fatty acids in the bloodstream are beneficial when energy demands are high, as happens during exercise or infection.
Under normal conditions free fatty acids have two fates:
(1) They can be burned inside the mitochondria to create cellular energy or ATP, or (2) They can be converted into sugar, via a process known as gluconeogenesis, which literally means forming sugar from anew. The later process is the body’s fuel preference during sleep and exercise, while the former process is used during stages of starvation, inflammation, and stress.
In lean and metabolically healthy persons, skeletal muscle is metabolically very flexible. During fasting or long duration exercise, fats are preferentially used for fuels. During intense, short duration, burst training, sugars are used to generate cellular energy. In contrast, the fat-burning furnaces—muscle tissue—of overweight and insulin-resistant subjects have a hard time burning lipids, and preferentially burn sugar (glucose oxidation).
Reverse Insulin and Leptin Resistance and Start Burning More Fat
1) Fasted Sprints. Researchers recently revealed how fasted sprints can powerfully increase leptin sensitivity in muscle tissue. Try three, 45-second sprints first thing in the morning, three days per week. (Taking caffeine before will help you burn more fat.)
2) Dynamic Weight Training. Many studies suggest that dynamic weight training performed four days per week, lasting at least 20 minutes per session (pushing yourself to failure), increases both leptin and insulin sensitivity.
3) Bring on the Hypertrophy. Well-defined muscles contain more leptin and insulin receptors and more GLUT4 transporters, all of which are characteristics of metabolically flexible, healthy muscle.
4) Cold Stress. Animal models have shown that cold thermogenesis can actually “brown” fat cells (that is, convert white adipose tissue to brown adipose tissue, which burns fats as energy to make heat instead of ATP).
-Keep the temperature of your house cool, in the 60s if you can.
-Take cold showers daily (hard in the winter, but well worth it)
-Jump into a cold body of water (if you live near a lake, ocean, or river)
5) Phytonutrient Stress. The color-derived compounds found in herbs, spices, fruits, and vegetables fine-tune our metabolic pathways, making us more insulin sensitive and better fat burners.
6) Manage Your Stress. Cortisol is very catabolic (breaks down healthy muscle tissue). Using HeartMath and being present will help prevent cortisol from eating up your muscle tissue.