Fasting in the historical sense means starving oneself for long periods of time. Long-term fasts are dangerous and elicit different effects on the body compared to intermittent fasting protocols. Within the first ten hours or so of calorie deprivation, the body depletes its blood sugar stored in the muscles and the liver (drains the sugar tanks) and switches to the use of ketones and fat for energy (the metabolic switch).
After a few days of fasting, the body begins to break down protein within muscles and fat to produce energy. Meanwhile, hormonal reactions will fluctuate. It’s well established that very long periods without food can cause a sizable drop in metabolism. This starvation mode is a set of adaptive biochemical and physiological changes that reduce metabolism in response to starvation, a phenomenon you definitely want to avoid. Short-term fasting does not put your body into starvation mode. Instead, your metabolism increases significantly.
Intermittent fasts should not promote fasting for longer than 36 hours. If you fast much longer, the metabolism boosting effects can reverse. What’s more, long-term fasts that trigger the starvation mode aren’t safe.Fasting intermittently coaxes the body to make changes and operate more efficiently. The different phases your body enters during your fasts is the catalyst for creating the phenomenal health benefits associated with this lifestyle. The process behind the magic is intriguing. Here I take a closer look at what goes on in your body when you begin to fast.
3 metabolic statesTo fully comprehend intermittent fasting, you need to understand the three metabolic states, which the following sections discuss in greater detail. The following sections discuss these three metabolic states. During any given day, your metabolism typically switches between the fed state and postabsorptive (after food has been digested) states.
The fed stateAlso called the absorptive state, the fed state happens right after you eat — when your body is digesting the food and absorbing its nutrients. As soon as you see or smell food, your mouth may start to water, and digestion has already begun. When the body is fed, glucose (the blood sugar from carbohydrates), fats, and proteins are absorbed across the intestinal membrane and enter the bloodstream to be used immediately for fuel or in the case of protein, used for muscle growth and repair.
If you exert energy shortly after eating, your body will process and immediately use the dietary fats and sugars that were just ingested for energy. If not needed, the excess glucose is stored in the liver and muscle cells, or as fat in fat (adipose) tissue. Release of digested nutrients into the bloodstream stimulates the pancreas to release the hormone insulin. Insulin stimulates the uptake of blood sugar by liver cells, muscle cells, and fat cells.
The postabsorptive stateThe postabsorptive state happens when the food has been digested, absorbed, and stored. No more nutrients are entering the bloodstream from the digestive system. Sugar concentration in the blood drops and the pancreas stops releasing insulin and starts releasing a different hormone, called glucagon. Glucagon directs the liver and muscle cells to release stored blood sugar back into the bloodstream for energy. The postabsorptive state is therefore the metabolic state occurring after digestion when food is no longer the body’s source of energy, and it must rely on stored blood sugar for energy.
The fasted stateThis state occurs when the body has depleted all its glucose stores. Shifting into the fat-burning state known as ketosis occurs after your body burns through your glycogen stores (the tanks of sugar stored in your muscles and liver). This is when the metabolic switch occurs.
The first priority for survival is to provide enough blood sugar or fuel for the brain (the brain must be supplied with fuel in the form of glucose or ketones, although sugar is the preferred food for the brain). The second priority is the conservation of amino acids for proteins. Therefore, the body uses ketones to satisfy the energy needs of the brain and other blood sugar–dependent organs and to maintain proteins in the cells. In the event that you fast too long, the body goes into starvation mode and begins to break down vital organs and muscle tissue as a fuel source.
It's important to understand that these highly orchestrated physiological events triggered during the fasted state carry over into the fed state to heighten mental and physical performance as well as disease resistance.
The important role of ketonesFor the brief period of time your body is in the fasted state, many physiological processes are at work that have healing properties. In addition to autophagy, another process going on is the metabolizing of fat in the liver that releases chemicals called ketones. Ketones circulate throughout the body and have many positive actions apart from serving as an alternative fuel source.
Ketones regulate the expression and activity of many proteins and molecules that are known to influence health and aging. Ketones specifically dampen inflammation, the condition associated with promotion of chronic disease. Ketones also interact with muscle cells to improve insulin sensitivity, reducing blood sugar levels.
Ketones are probably most recognized for their healthful effect on brain function. Ketones have a neuroprotective effect, shielding the brain against age-related cognitive decline. It has been known for 50 years that ketones can benefit people with epilepsy and reduce seizure frequency. Ketones, most notably a ketone called beta-hydroxybutyrate, has been shown to increase production of brain-derived neurotrophic factor (BDNF), the protein that keeps your brain strong and resistant to neurodegenerative disorders (Alzheimer’s disease and Parkinson’s disease are the two most common neurodegenerative disorders).
Switching back and forth between fasting and healthful feeding is the key to providing the unique benefits of intermittent fasting. Prolonged ketosis, such as occurs when you follow a Keto Diet, is a flawed approach to long-term health because the diet itself has been linked to digestive and gall bladder disorders as well as a reduced ability to exercise. People who follow a high-fat, low-carb fad diet for prolonged periods have been shown to be at increased risk for cardiovascular disease and premature death.
The facts on fatLike it or not, your fat cells are with you for life — even if you lose weight. When you lose weight, your fats cells (also known as adipocytes) simply shrink in size. Fat cells are very flexible, able to grow or shrink dramatically, and can change in size by up to a factor of 50! Most fat cells are created during childhood, stabilizing in early adulthood. Unfortunately, new research shows that although you can’t get rid of the cells themselves, (unless you resort to liposuction), if you continue to overeat, the number of fat cells in your lower body is capable of increasing throughout life. In adults, fat-cells increase in lower-body depots after only eight weeks of increased food intake.
When you fast, you increase the amount of fat in the fat cells burned for energy. Over the long term, and if you’ve succeeded in creating a sustained calorie deficit (you routinely burned more calories than you consumed), you’ll reduce the size of your fat cells.
Just make sure that you don’t refill your fat cells by reverting back to old habits. Permanent weight loss requires making healthy changes to your lifestyle and food choices. Here are tips for keeping the weight off:
- Practice daily exercise.
- Slow and steady wins the race.
- Continue to set goals to keep you motivated.
- Find a cheering section.
- Get plenty of good quality sleep.
Intermittent fasting is here to stay because it’s flexible. You can choose an intermittent fasting practice and nutrient plan that fits your lifestyle. You may first choose a plan to help you lose the flab, but soon, I guarantee, you’ll make it a routine way of life as you tap into the notable physiological effects, such as gaining more energy, inner calm, and mental clarity.
Rev up your metabolic rateYour metabolism is the sum total of all the complex biological processes your body performs to turn the calories you eat and drink into energy. People with a higher metabolic rate can eat more calories to sustain their body weight than people with a lower metabolic rate.
Intermittent fasting affects your metabolic rate, depending on the length of the fast. So how does intermittent fasting affect metabolism? Intermittent fasts are short-term fasts. Contrary to what many believe, short-term fasts have been proven to boost metabolism by 3.6 percent to as much as 14 percent! This phenomenon is primarily due to the drastic increase in blood levels of norepinephrine, released during fasting periods.