Our lives have become so modern and convenient that sometimes it's hard to imagine what it was like when food was not fast, easy, and readily available. But our ancestors had a very different experience, often going for long periods without eating. As such, their bodies had to be prepared and evolved to be able to withstand harsh conditions and long periods of time without food.
They did this through metabolic flexibility. And to be clear, metabolic flexibility is the body's ability to shift back and forth between using glucose (from carbohydrates) and fatty acids (from fat) for fuel.
This is how your body fuels itself.
The human metabolism is a complex system, but here's what you need to know to understand how our bodies use food to produce energy: When we eat (especially carbohydrate-loaded foods) our insulin levels rise, which stimulates our cells to take in glucose. Then, the cell's mitochondria will use the glucose to make ATP, or energy. Any glucose that is excessive of what the body needs will then get stored as glycogen, and any fat that isn't utilized gets stored as well (via a process called lipogenesis). During periods of fasting or starvation, the body calls upon this stored energy. And the longer the fasting period, the more the body will eventually revert to lipolysis, or the breakdown of fat to fatty acids to use for fuel.
Metabolic inflexibility messes with insulin levels.
In today's modern world, overeating, processed foods high in sugar and trans-fats, and lack of physical activity have led to a rise in obesity, diabetes, other diseases, and metabolic inflexibility. The more we eat (especially carbohydrates and sugar) the more insulin is released over time, which eventually results in insulin resistance. This means that the body can no longer respond well to the insulin signals, leading to higher and higher levels of insulin circulating in the body. The result is that the body (especially the mitochondria that produce the energy) become confused, losing the ability to make the switch from one fuel source to the next; fats end up getting stored and metabolic inflexibility ensues.
You can train your metabolism to keep you healthy and fit.
If you can't go for long periods without eating, feel like you need to take a big snooze after a meal, feel lethargic more often than not, or you have a hard time losing weight despite dieting—you may be experiencing metabolic inflexibility. The good news is that even for those individuals who are genetically predisposed to metabolic inflexibility, changing lifestyle behaviors and feeding times can actually help to reset the body. Here are four ways to take charge of your metabolism and regain metabolic flexibility:
1. Exercise with variety.
The more active you are, the more energy you will need and the more your body will require the breakdown of fuel sources. So ramp it up and bring in variety. Your body will have to reset itself each time you go faster, lift heavier, or do something your body isn't used to. Aim for variability in your workouts and every now and then, throw in an activity your body is not used to doing, be it hiking or lifting weights.
2. Cut down on carbohydrates.
The fewer carbohydrates you ingest, the more often your body will have to rely more on fat for its fuel source. You want to cut out completely refined grains or sugar (even juice), processed foods, dairy, and eat less than two pieces of fruit a day. You may also want to try following a paleo diet for three to four weeks and see how you feel. If you are prone to inflammation, have an inflammatory disease or history of cancer, you may likely also benefit from trying a ketogenic diet, which is also low in carbohydrates.
3. Boost your metabolism with antioxidants.
Altered metabolism has been closely linked to oxidative stress and inflammation, and the use of antioxidants in nutritional plans has been shown to have a positive influence on this. You can increase your intake of antioxidants by eating dark leafy greens, berries, and other fruits and vegetables that come in a variety of colors. You can also add in spices or supplements containing curcumin and green tea extract, two of the many different antioxidants that are powerful in aiding metabolism.
4. Follow early time restricted feeding (eTRF).
You may want to check how long you can go without eating by fasting for short periods of time. Try starting with three hours, eventually extending it to 12. For instance, allow your last meal of the day to be at 5 p.m. and don't eat again until 5 a.m. Some studies show that getting all your calories in the morning window when your metabolism is supposed to be most active and then fasting from early afternoon on, improves your metabolism and helps with weight loss.
The concept behind eTRF is that it causes your body to move to fat stores for energy and positively affects the circadian rhythm of your body. The circadian rhythm of the body is normally influenced by light and dark cycles and is also controlled by feeding and fasting cycles—meaning that the circadian clock controls the body's metabolism to be active or inactive. When you do eTRF, the active cycle of metabolism increases after the long period of fasting, so that you break down more fat for fuel.
Connect with your body's original design.
It may all sound a bit complicated, but try to think about our ancestors, what they ate, and how often. Try to avoid the center aisles of the grocery store and eat what naturally grows from the earth. Eat lots of vegetables, a few fruits, less grains, good healthy fats, grass-fed and hormone-free proteins, and some nuts and seeds. If you want to become leaner, try eTRF and see how it goes!