The theory goes like this:-
So far as your body is concerned you are either in a FED state or a FASTED state.
(There is an in between post–absorptive state but for now let’s keep it simple.)
FED State – After eating the pancreas secretes insulin which signals the removal of excess calories (energy) that you are not immediately needing to use, into fat stores. Meanwhile the burning of fat is turned off and the body burns glucose from your last meal.
FASTED State – Here the insulin levels are low. (In contrast the opposing hormones Glucagon and Growth Hormone levels are high.) There are no freely available calories as we’ve not eaten for a while, so the body calls in its reserves – Fat is converted to Glucose in a process called Gluconeogenesis quite literally translated as ‘the production of new glucose’. However, this will only occur beyond around 8 hours of fasting when liver glycogen stores, the readily mobilised energy store useful for sudden, strenuous activity start to deplete and an alternative source of glucose is required.
If we spend much of our time in the FED state insulin is constantly high and the body will avoid burning stored fat and this chronic exposure leads to ‘insulin resistance’ where the body secretes even more insulin in response to the FED state. This is the cause of ‘Metabolic Syndrome’: obesity, abdominal fat storage, high triglycerides, low HDL or “good” cholesterol and elevated glucose with eventual type 2 diabetes.
When these “sugar burners” stop eating for a few hours they run out of glucose from their last meal and instead of transitioning to the FASTED state and mobilising and burning stored body fat, they become hungry for more glucose from carbohydrates and can spend much of the day trapped in a cycle of eating every few hours, spiking glucose and thus insulin and then becoming hungry again. (See the ‘hypoglycemia’ myth below)
However, we can change this state and become “fat adapted”, the metabolic state your body is in once your body has efficiently transitioned from burning sugar to burning fat reserves for energy. We can become better fat adapted by the traditional methods of eating less and burning more calories – Diet & Exercise. Newton’s first law of thermodynamics – The law of Conservation of Energy, states that energy (measured here in calories) cannot be created or destroyed in an isolated system and thus if we consume less calories – eat less and burn more calories – exercise more, our body, the ‘isolated system’, will lose weight as we will use up our stored energy = fat!
Less calories results in less available glucose, so the body must rely more on stored body fat.
Eating a LCHF (Low Carb High Fat) diet improves the body’s ability to utilise fat for energy rather than glucose, as there is more fat and less glucose available at all times, even in the FED state.
High-intensity exercise depletes glucose and glycogen rapidly, forcing the body to utilise more fat for fuel. Exercise also improves insulin sensitivity. Fasted cardio is exercise done in a FASTED state, in which your body is no longer processing or digesting food, the benefits include increased lipolysis, fat oxidation and decreased insulin levels, essentially using stored energy and thus losing weight. (Or more accurately losing fat whilst building muscle.) Also see below ‘High-Intensity exercise helps with fat adaptation.’
Think Parkrun! 9am Saturday Mornings – https://www.parkrun.org.uk/
This seems to be another way to lose weight by spending more time in the FASTED state we encourage the body to burn more fat.
Some say the 16:8 diet is the easiest way to do this. Skip breakfast, have a light lunch and a larger dinner.
16 hours of being in a FASTED state and 8 hours being in a FED state.
FED state starts with a meal (seemingly no matter how small – Yes even milk in your coffee!) and lasts for three to five hours whilst your body digests and absorbs the food, insulin rises significantly shutting off fat-burning and excess calories are stored as fat. (The post–absorptive state lasts until 8 to 12 hours after your last meal whilst the components of the last meal are still circulating.)
FASTED state starts 8 to 12 hours after your last meal and is when the body can burn fat in the absence of glucose.
So with a typical diet of breakfast, lunch and evening meal it’s not difficult to see why we may seldom be in a FASTED state especially with late evening snacks and sugary drinks and so we may find we are almost always in a FED state.
Eating carbohydrates, especially refined carbohydrates with no fibre boosts the FED state, as carbohydrates raise both glucose and insulin higher than other macro-nutrients (fat, on the other hand, raises glucose and insulin the very least). In general, when you eat a meal, your body spends a few hours processing that food and burning what it can from what you just consumed. Because this energy is readily available and easy to burn your body will utilise this energy rather than the hard to get at fat you have stored. This is especially true if you have just consumed carbohydrates, because these are rapidly converted to glucose and your body prefers to burn sugar as energy before any other type – fat etc.
High-Intensity exercise helps with fat adaptation as it utilises glucose and glycogen rapidly, forcing the body to switch over and utilise more fat for fuel. This means that a meal immediately following a workout will be stored most efficiently: mostly as glycogen replenishing muscle stores, burned as energy immediately to help with the recovery process and have only a minimal amount stored as fat. Exercise also improves insulin sensitivity.
“Breakfast is the most important meal of the day”
When we wake insulin levels are low and you may be just entering the FASTED state. Breakfast will thus spike glucose which raises Insulin and shuts off fat-burning!
Breakfast cereals also contain a lot of natural and added sugar and high spikes of insulin and glucose lead to large drops in glucose a few hours later triggering hunger (although NOT true hypoglycemia – low blood glucose.) Some say that this fits with our evolutionary heritage when in the morning we would be hunter Gatherers and eat later in the day. Break out of Breakfast – fast!
(Does the cornflakes GI surprise you? – It does me!)
“Eat small frequent meals.”
Although this MAY result in one taking in less calories in order to burn fat we do need to be in the FASTED state, which frequent meals precludes.
“Eat protein frequently throughout the day in order to build muscle.”
Protein is an important building block of bones, muscles, cartilage, skin, and blood but eating an adequate amount once a day is plenty to build and repair tissues, make enzymes, hormones and other body chemicals.
“Fasting leads to burning muscle instead of fat.”
Growth hormone is increased during the FASTED state as well as whilst we sleep. If insulin is the FED state hormone, Growth Hormone is the FASTED state hormone and can rise 2000% after a 24 hour fast!! Growth hormone builds muscle due to its anabolic effects – Body builders use it to build muscle and burn fat! Growth hormone elevates in the FASTED state to help preserve muscle! This makes sense as our hunter-gatherer ancestors would have needed this to be the case so as to avoid weakening muscles and allowing the hunt to be successful! When we are in the FASTED state we also release catecholamines (epinephrine or adrenaline, norepinephrine, and dopamine) increasing energy and alertness further helping the catching of prey!
“Your metabolism slows down when you are fasting.”
Actually, our metabolism might actually speed up slightly thanks to the release of catecholamines and activation of the sympathetic nervous system the “fight or flight” system. This would fit the theory above that hunter gatherers would be activated during the day when most active and in the FASTED state looking for food, followed by parasympathetic “rest and digest” mode (The in-between post–absorptive state and the FASTED state.) in the evening after eating a large meal.
“If I don’t eat I will get low blood sugar [hypoglycemia].”
FASTING for extremely long periods rarely results in hypoglycemia. The sensations of “low blood sugar” (in non-diabetics) usually results from eating very high glycaemic index (GI) carbohydrate food a few hours earlier, inducing a blood glucose spike, raising insulin resulting in a ‘crash’ in blood sugar levels and it is this rapid drop which causes the ‘light-headed’ sensation and a desire for a carbohydrate fix!
The most common form consists of skipping breakfast every morning with lunch at noon and dinner at 8:00 p.m. Snacking inside your eating window is allowed although its best to consolidate calories into larger meals rather than intermittent snaking. This is the 16:8 split (16 hours fasting and 8 hours eating.)
An alternative but rather more difficult in practice routine is the warrior diet which involves fasting for 20 hours overnight and during the day and then possibly ‘overeating’ during a four-hour window in the evening. This is again based on our primitive ancestors spending their days hunting and gathering and feasting at night. This is a 20:4 hour split (20 hours of fasting and then a 4 hour eating window at the end of the day) does allow you to eat large satisfying ‘anything goes’ meals at the end of the day and might be perfect if going out to dinner where several highly calorific courses food might be involved. Fasting this long during the day is more difficult but does lead to a deeper level of fat adaptation and low insulin (which helps improve insulin sensitivity).
So an alternative to all those other diets that don’t seem to work? Some science but remember there is controversy in all this! Try it and see – I’ve seen great results in others – me? I’m at the beginning – early days – hungry up until lunch but enjoying the freedom to eat an ‘unrestricted’ supper! Not lost any significant weight YET!