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.
So, during the IF period you will be consuming less than normal but in the feeding period you will be consuming more than usual in that set period of time to balance your overall food intake. Remember – at the end of the day your overall calories determine your fat loss, maintenance or fat gain.
If you are burning more fat in a certain period of time it will not magically result in more fat loss over the course of the day and week because remember that in the feeding period you will be storing more fat than usual and this counterbalances over the course of 24hours.
So, does it speed up fat loss beyond normal measures? No. Does it have its positive benefits and place in a diet plan? Yes, depending on the individual client’s preferences and lifestyle. The way that it can improve fat loss is that it can have profound effects on a person’s ability to adhere to a diet and be able to reduce their overall energy intake by consuming less meals and or food.
IF and performance:
As mentioned above, when we fast our body releases two of our ‘stress hormones’ cortisol and adrenalin and when we train fasted it upregulates our ‘flight or fight’ response increasing our adrenalin and keeping our cortisol levels high. This does have positive performance affects as this sudden release of adrenalin brings with it a stimulant like energy which can feel euphoric – this can improve focus, energy, and creativity. This isn’t an increase in physical performance but definitely one of mental performance so the application of fasting can be used in more than just a training environment but may help with performance in a business and creativity environment as well.
This however doesn’t work for everyone and again is very anecdotal and individual for each person. Some people may attempt to fast for a longer period of time than they are use and or train in a fasted state and feel terrible. As with anything though, this overtime becomes easier as your body adapts but doing longer fasting periods or training fasted simply isn’t for everyone.
IF increases fat loss over and above a normal diet plan?
FALSE! As mentioned above, although burning more fat during the fasting window, the fasting window is followed by a feeding window and during this time more fat will be stored. What determines fat loss is the overall intake of calories over the ENTIRE course of a day and then a week. So, burning more during fasting period ok, consuming more during feeding window ok, but if you end up with a net zero then you won’t be burning more fat or gaining more fat at the end of the day. It comes down to your overall calorie intake that fits in with your diet plan of weight loss, maintenance, or weight gain.
IF will result in increased muscle loss?
Training fasted will increase muscle degradation but following the fasted training, the meal you consume post workout will have an amplified anabolic effect as your muscles are more sensitive to insulin. So, again this will result in a net zero.
It then comes down to your diet goal, maintenance, fat loss or muscle gain. If you are hitting your overall caloric targets and your overall protein target that fits with your plan, then IF won’t have a significantly negative effect on muscle loss or gain.
The only time when it will potentially increase muscle loss beyond normal measures is when you are fasting before AND after a training session. There is a small amount of evidence that shows if you continue to fast 2-3 hours after a fasted training session, that stress hormone cortisol will be raised so high that muscle loss exceeds what the following meal can counteract. So, consuming a meal shortly after a fasted training session is a good idea
IF caused your blood sugar levels to drop too low?
This is a totally unfounded fear as we contain a hormone in the body called glucagon. Glucagon serves to keep our blood glucose levels high enough for our body to function well. When blood glucose levels start to become low, glucagon is released and signals the liver to release glucose into the blood. It has the opposite effects that of insulin as the two hormones work in partnership to help keep the blood glucose levels balanced.
Can increase ‘metabolic efficiency’ – your body’s ability to use fat as fuel more efficientlyCan improve insulin sensitivity especially in very overweight individuals or people with insulin resistancePost fasted training meal can be stored more efficiently straight into the musclesCan help diet adherence
Who can it benefit:
Anyone in the right contextPeople who train early in the morning and don’t feel like consuming something before the session or simply don’t have time to consume something before the session.People who don’t enjoy breakfastThose who suffer appetite and hunger controlPeople who live a hectic lifestyle and may not have the opportunity to consume breakfastIndividuals with a low stress environmentThose looking for fat loss via a manageable calorie deficit
Less time to consume an adequate amount of calories in the day as the feeding window reducesDecreased frequency of muscle protein synthesis with less meals being consumed – may have a small effect on muscle gainIf you suffer from binge eating and use IF as a way to binge at certain times of the day – could create an unhealthy relationship and mindset with foodMay have a negative effect on female hormone production and health if used long term. This is very individual and needs to be monitored closely by a health care professional.
Who may it not be good for:
Athletes or people who need high volumes of food, protein and nutrient delivery to perform wellHighly stressed individualsIndividuals who like breakfastPeople who struggle with hunger pangs and fasting exacerbates the hunger pangsPeople with hormonal issues
Intermittent Fasting is simply a dietary protocol that can be beneficial in certain situations and detrimental in others. It all comes down to the individual, their current health status, their lifestyle habits, training regime, and dieting history and habits. It can be a very useful tool to help you achieve your health and fitness goals, but again it all depends on the individual.