Activating The Metabolic Switch and Its Impact On Our Health and Body
Fasting and time-restricted eating have become more prevalent in our culture again. Weight loss being one of the main reasons. However, compared to a normal calorie restricted diet, fasting and time-restricted eating provide the same results. So why is fasting and time-restricted eating becoming so popular again?
The most likely answer is our culture's movement from curing disease to preventing disease. People are starting to look at their health span and not just lifespan anymore. Afterall, what good is living to a 100 when the last 10 years are spent bed-ridden and dependent on caretakers.
The Metabolic Switch
Our bodies, including all mammals, have evolved very complex systems to enable us to survive when food is not available. Not only survive, but still be able to function properly and be able to fight or run if the need arose.
Without these systems, none of our ancestors would have survived prior to the industrialization of food. Unfortunately, our bodies do not evolve at the same rate as our industries do. As food has become readily available year round and our pantries always well stocked, our bodies simply have not caught up.
Simply put, when we eat we store calories in our body as fat to provide energy when food is not available. In today's world, that time never comes and our body is in a constant state of calorie storage.
You may be telling yourself that when you lose weight by restricting calories or creating a calorie deficit, you are using your body’s stored calories. And you are 100% correct. However, when you restrict calories, you never activate the body’s metabolic switch.
The metabolic switch is a term used to describe our body changing its primary energy source from glucose to ketones. It’s an important switch that the body has evolved to protect our body and help us survive.
Besides switching between primary energy sources to fuel itself, there is a cascade of metabolic changes in the body that occur. For instance, the body switches from anabolism to catabolism, or simply put, switching from building to breaking down.
Certain proteins like mTOR-1 get turned off, which results in protein synthesis stopping in the body. This may not sound good but being in a constant state of building causes disease later in life, cancer being one of the top ones.
When the body stops building it activates certain cells to scavenge and breakdown old cells and proteins. Although simplified, think of this as you cleaning your house and the trash crew coming by to pick up the garbage. Imagine what your house would look like if you kept adding stuff but never took anything out!
Even though catabolism during calorie restriction results in muscle loss, activating the metabolic switch activates a protein or muscle sparing phase. Simply, when the body switches to using ketones, it prevents itself from breaking down muscle.
Activating the switch on a consistent basis can also result in improved insulin sensitivity, decreased chronic low-grade inflammation, blood pressure and resting heart rate, and decreased overall risk for cardiovascular disease, type II diabetes, and cancer.
Activating the switch
Okay, so now we know that the metabolic switch is an important evolutionary process of all mammals and needs to be activated on a regular basis to maintain the health of our body. But how do we activate this switch?
The metabolic switch is dependent on the glycogen stores in our body. Once the glycogen gets depleted in the liver the body switches to using ketones. These ketones are derived from free fatty acids released from fat cells.
Glycogen depletion typically occurs between 12-24 hours of fasting and is heavily dependent on how active the person is. For example, an active person would deplete their glycogen stores sooner than someone laying around all day.
You can also activate the switch by eating a ketogenic diet which consists of high fat intake and less than 20 grams of carbs per day.
Although newer research is coming out that the body needs to go through an amino acid fast as well for cardiovascular health reasons. This would mean that you would have to eat strictly fat with no protein and carbs for a short period of time to obtain the greatest health benefits.
For this reason, the better choice is either whole day fasting or time restricted eating to activate the switch. Once the switch is activated you can now consume a keto style diet to maintain the use of ketones as the preferred fuel source.
Once you consume carbohydrates you flip the switch back to using glucose as the primary fuel source and glycogen stores begin to be refilled.
Activating the metabolic switch
Time restricted eating
Eating only during a 4-8 hour window each day, 20-16 hours fasting.
Can be done on a daily basis
Whole day fasting
Not eating anything for a full 24-36 hours
The fast starts from the time of your last meal
Is ideally limited to only 1-2x/week to prevent malnutrition.
Keto diet
A high fat diet with less than 20 grams of carbs/day
Saturated fat should not exceed ~5-10 grams/day as high intakes of saturated fat are a cause of cardiovascular disease.
Healthy fats (mono-unsaturated and poly-unsaturated) should be primary source of calories.
*Although there are other methods of activating the metabolic switch, these are the most straight forward and simple options for the majority of people.
If you are interested in learning more information on the metabolic switch and how it can impact your overall health and health span, contact me at dietitian2go@gmail.com.
If you would like guidance and coaching with time restricted eating or whole day fasting, schedule an appointment with me here.
Written by: Adam Skowyra MPPD, RDN, LD
