Intermittent fasting (IF) is not a diet but rather a dietary pattern that you can follow.
IF is a conscious decision to skip certain meals or spend a certain longer period of time without food.
IF is not all that new either, each and every human being fasts on a daily basis, whether you really it or not. We intermittent fast by default from the time we consume our last meal of the day until the time we wake up and consume our first meal of the day, usually around the 8-10-hour mark as we are sleeping in between these two meal times and this is a fasting period (period of time without food).
There are many different variations of fasting as the time of the fasting window increases, but fasting does not have to be a strict protocol. If you wish to fast then as long as it suits your diet goal and lifestyle then it can be used as a beneficial tool to help in line with your goals.
The most common type of fasting and one that is consistently promoted is the 16/8 fast. Meaning fast for 16 hours and consume food in a 8 hour window. This is most easily applicable by starting your fast from the time you consume your last meal of the day until around lunch time the following day. There are many potential benefits of IF but it doesn’t mean it is for everyone or suits everybody’s lifestyle and diet goals.
What happens when we fast?
When we consume a meal, our body spends the next few hours processing and digesting the consumed food, burning and using what it can from that consumed meal or storing it in the body as glycogen or body fat to be used as a fuel source later on.
When we are in a ‘fasted state’ we don’t have the immediately available energy from a meal we have just consumed, so our body then has to rely on our stored fuel sources of the stored fat and glycogen in the body as energy.
The same principle applies when we are training ‘fasted’. Without the immediate available fuel source, our body then relies on our stored energy in the cells to be released and power us through the training session.
So, when we are fasting or training fasted, depending mostly on the training intensity, our body will be using the stored glycogen in our muscles and liver to provide us with energy predominantly and or the stored fat in the fat cells within the body. By depleting the stored muscle and liver glycogen it will improve our ‘metabolic efficiency’ or ability to ‘tap into’ our stored fat as fuel by forcing your body to do this when glycogen stores get low. But, this depends on training intensity and duration. If we are moving and training at lower intensities then our body is using our aerobic energy system (oxidative energy system) which means the body will be oxidizing fat as fuel as its preferred fuel source. Once we hit a certain intensity that is higher we start to tap more into the anaerobic energy system and glucose and stored glycogen becomes the preferred fuel source.
Its effects on your hormones:
IF can be extremely beneficial when looking at improving the insulin sensitivity of a person. Often with clients who potentially have insulin resistance (a term given to a condition where the body’s cells fail to respond normally to the hormone insulin, resulting in blood glucose levels that are exceedingly high over a prolonged period of time, which can lead to diabetes and other health issues), I will implement some sort of fasting strategy which will lower the consistent feeding patterns of the person, and give their digestive system, and storage hormones a rest in which will improve the insulin sensitivity of the cells.
Fasting also increases the release of cortisol and adrenalin. Both hormones are extremely important and play many roles in the body but in this context, they upregulate lipolysis – meaning they help fat cells release fatty acids into the blood stream to be used as fuel.
However if you are a highly stressed individual then you will already have high cortisol levels which can lead to long term health problems and short term problems like reducing the quality and quantity of your sleep, reducing appetite, and causing big blood sugar level fluctuations. If this is you, fasting may exacerbate these issues and be more problematic than beneficial.
Intermittent Fasting and Fat loss:
A misconception is that IF and training fasted is a tool that can be used to speed up fat loss regardless of your overall calorie intake and macronutrient breakdown. This is false because following a fasted period comes a feeding period.