Intermittent Fasting and Time-restricted eating…are similar, but no the same. Time-restricted eating means that you only eat within a specific time frame. For example, eat during an 8- to 12-hour daytime window and fast during the remaining 12 to 16 hours.
Unlike intermittent fasting, which involves caloric restriction, time-restricted eating allows a person to eat as much as they want during the eating window. Now that we understand the definition of time-restricted eating and intermittent fasting, let’s better understand what happens to your body with fasting.
When you eat a ‘normal’ meal….glucose (from carbs), and fatty acid (from fats) are the main energy sources for your cells. After you’ve eaten, glucose is used as a direct source of energy, and fatty acids are stored in your fat tissue in the form of triglycerides.
When you fast…meaning you are eating nothing or very little, your body runs out of glucose and needs an alternative source of energy to keep going. It now breaks down your triglycerides into their individual components (fatty acids and glycerol) and then your liver will convert the fatty acids into ketone bodies.
Ketone bodies (or ketones for short) can be used as an alternative source of energy for many tissues, including the brain. When you are eating enough food (from all 3 macronutrient groups- carbohydrates, proteins, and fats), the amount of ketones in your blood are low. When you fast, this level rises within the first 8-12 hours reaching levels of between 0.2-0.5 millimolars (mM) which are maintained for about 24 hours with a subsequent increase to 1-2 mM by around 48 hours. However, fuel is not ketones only function, they also have major effects on your cells and organs. For example, ketones able to:
1. Improve mitochondrial function
Mitochondria are often referred to as the powerhouses our cells. Energy in our body is mainly from the process of mitochondria releasing energy from ATP molecules. When we suffer from metabolic disturbances and obesity, our mitochondrial function is reduced….but fasting may help to improve this function.
2. Help your cells become more resistant to stress
During these times of food restriction, the cells adopt a stress resistance mode. Essentially you are making your cells tougher so that they can withstand more.
3. Enhance autophagy
Autophagy, which is Latin that stands for “self-eating,” refers to when cells purposely eat other cells in your body. They might sound like a bad thing but its not. Autophagy gives your cells the ability to clean up “cellular garbage” that normally accumulates in cells or when you are hurt or sick. Basically it’s your cells version of taking out the trash! When autophagy doesn’t work properly, your immune system attacks this cellular garbage and can cause low grade, chronic inflammation (which is the basis of most chronic diseases).
4. Help Recovery
When you eat (or break-your-fast), the body is forced to switch from fasting and using ketones to glucose…this is known as ‘metabolic switching’.
Depending on what you eat, there will be an increase in glucose and your ketone levels will decrease. In the recovery period, there is an increase in the formation of proteins, and in this phase, we see cell growth (including mitochondrial growth), as well as cell plasticity (which is the ability of your cells to adapt to changes in their environment). The ‘metabolic switching’ between fuel sources links fasting to a number of long term health benefits. The key seems to be not to stay in ketosis indefinitely (like what the keto diet is about), but to regularly swap between ketones and glucose.
Additional health benefits come into play because fasting goes hand in hand with our natural circadian rhythm. Your circadian rhythm is your body’s natural clock that links various biological processes to day and night. You could think of almost every cell in your body as having a tiny biological clock that syncs up with the master clock located in you hypothalamus, in the center of your brain. Your master clock sends signals to the body clocks throughout the day to regulate your daily activities. The master clock is very sensitive to light and having appropriate exposure to light during waking hours helps to keep you alert. As night falls, the brain clock initiates the production of melatonin, helping to lull you to sleep.