Is There A Healthy Way To Diet?
The Science Behind Fasting
In 15th century Italy, a Venetian nobleman, Luigi Cornaro, at 35 years old was weak, sick and dying. On the advice of his doctor, Cornaro began to eat as little as he could. He immediately pledged to adhere to a “quantifying principle”, restricting himself to only 12 ounces of food (bread, egg yolks, meat, and soup) and 14 ounces of wine a day.
Cornaro would go on to live to be 98, writing four books after the age of 83 describing his lifestyle. This was a remarkable feat at the time, one he fervently attributed to his strict dietary regimen. Cornaro’s story proves that the idea of conscious food restriction – dieting – isn’t a new one. In fact, calorie deprivation goes all the way back to the beginning of life itself.
Mother nature is harsh and only the select few survive her wrath. Species need to find their niche in nature, with effective strategies to successfully survive and reproduce. Food, shelter, security and a mate are the fundamentals that encourage procreation and reproduction, which in itself can be demanding and even dangerous. Fertility requires adequate nutrition in preparation for pregnancy.
During times of scarcity, animals switch into survival mode, using stored calories, breaking down and recycling flawed cell components, and gradually gearing down metabolism to conserve energy and wait out the famine. In this way, evolution developed and honed adaptive strategies to increase survival in the face of calorie restriction. Those relatively few survivors throughout history passed on those genes to us. As such, it might make sense that we can survive, and possibly even thrive, under similar conditions of intermittent scarcity.
Despite having elegant and powerful biological strategies to cope with short periods of food deprivation, the idea of fasting and fad diets is increasingly equated with abstinence, poor health and even rebound obesity. As we increasingly live in societies blessed with an abundance of calories masquerading as food, someone has to bite the bullet and eat all that ‘food’. Consequently, modern official diet doctrines strongly promote 3 meals/day (plus snacks!) following the flawed food pyramid guidelines – a whole new way of eating for humans that differs drastically from that of our ancestors.
Questioning the official doctrine in the face of the exploding obesity and sickness epidemic is not surprising and is consistently a hot topic for debate. So which diet is right? Vegan or vegetarian, ketogenic, carnivore, paleo, or Mediterranean? It’s hard to say. There’s a wealth of research studying these diets and quite often there is conflicting evidence. But more importantly, these studies often fail to control for a very important variable: when we eat.
Despite efforts to eat a healthy diet, rates of obesity and metabolic diseases continue to rise. Most diets have had limited success because of how difficult they can be to follow. Dieters find themselves in an overwhelming conflict with their bodies, their families and their food supply. Perhaps eating right doesn’t have to become such an obsession.
This has led researchers to investigate alternative methods that will allow dieters to keep eating their favourite foods. Intermittent Fasting (IF) is one method that is gaining popularity because of its ability to specifically target body fat without excessive and onerous foods restrictions.
This is where we begin our journey into the effects of fasting.
The Different Fasting Methods
Intermittent Fasting (IF)
This is a term that encompasses both Alternate Day Fasting and Time-Restricted Feeding and is defined by cyclical periods of fasting and feeding.
Alternate Day Fasting (ADF)
Fairly self-explanatory - fast one day, eat the next.
Time-Restricted Feeding (TRF)
This fast involves eating in a smaller window of the day. A common TRF protocol is 16:8; all your meals are eaten in an 8-hour window followed by a 16-hour fast.
Caloric Restriction (CR)
Caloric Restriction involves eating only a percentage of the calories you would typically eat, with no time restrictions. For example, someone normally eating 2500 calories switching to a 60% calorie restricted diet will consume 1500 calories/day. This is the typical diet strategy that has let so many down in the past.
Time-Restricted Feeding (TRF)
Time-restricted feeding (TRF) and its purported health benefits are the focus of this article. TRF has often shown similar benefits to other kinds of IF that include reductions in blood glucose, reductions in total fat mass without reducing lean mass, and improved insulin sensitivity. However, compared to other fasting methods TRF offers a shorter fasting period and no restrictions on what you can eat during your feeding time. It is for these reasons that following a TRF protocol may become the easiest and most successful way to get the benefits of fasting.
Before we delve too far into the implications of a TRF diet, it’s important to understand what is happening in the body through the fasting process.
After eating, carbohydrates are broken down into simple sugars that can be absorbed through the gut wall. These sugars are filtered through the liver, and can either be sent into the blood, stored in the liver (as glycogen – the storage form of sugar) or converted into and stored as fat in the liver and around other organs and muscles as adipose tissue (white fat).
Hours after your last meal your blood sugar begins to decline as it is used for energy. To offset this drop, the pancreas signals to the liver that the blood is running low on glucose. The liver responds by breaking long strands of glycogen into glucose and releases it into the bloodstream, bringing the levels of blood glucose back up. For 8-12 hours after your last meal the body primarily uses liver glycogen to maintain adequate blood glucose levels. It is after this point that liver glycogen stores are depleted enough that we start to make glucose from stored fat.
A molecule of stored fat, called a triglyceride, has a structure resembling a 3-legged jellyfish – a head with 3 tails. When we resort to burning fat, our adipose and liver cells break these triglycerides apart. The tails are transported to other cells of the body that use them for energy, while the heads are sent to the liver where these ‘fatty heads’, called glycerol, are turned into glucose and released into the blood in a process called gluconeogenesis (new glucose formation).
This is how we start to burn that insufferable belly fat. When given the choice, most tissues will use sugar as its energy source because it can be metabolized faster and enables us to conserve those precious fat stores for a needy day. Through regular fasting, we are able to burn body fat while simultaneously making necessary sugar for the blood and organs. Our body has the capability to make its own sugar; it makes sense that we don’t need to eat it all day long!
When we continually store fat instead of using it, we train our body to rely on a frequent flood of glucose. This leads to elevated insulin, and potentially insulin resistance, which explains the high correlation of obesity and Type II Diabetes. In contrast, when we fast for extended periods of time, we allow our body to mobilize our fat stores and keep insulin levels low. In this fasted state we also activate autophagy.
What is Autophagy?
Autophagy is the cell’s method of cleaning house - the process of breaking down dysfunctional or unnecessary parts of a cell. This is an essential practice of every cell in the body.
By removing expired structures the cell is able to clean up and recycle the proteins that make up these structures and put them to better use. After fasting for roughly 16 hours or more (depending on what you eat before you fast) autophagy is turned on. Feeding halts autophagy so that the cell can focus on the incoming supply of new nutrients.
The cells’ ability to repair themselves partly explains the benefits that have been seen with TRF. By shortening the feeding window, and thus extending the fasting window, autophagy has more time to run. This can be likened to a short-staffed, 24-hour restaurant. If this restaurant’s staff has a constant stream of hungry customers, their time and energy will be spent on preparing and serving food. This can be maintained for a short while, but eventually, the dishes start to pile up and the workers get tired. Without a break in the line of customers, the restaurant can’t catch up. This is precisely what happens to your cells when they aren’t given a long enough break from metabolizing food.
Our bodies have two different nutrient operating systems (OS). The first, our feeding OS, runs during and in the immediate hours after we eat. For many people, the feeding OS starts up just after waking up to an early breakfast and only turns off hours after we have gone to sleep following a late night snack. The feeding OS responds to incoming food particles by signalling to our cells that they have the resources needed to grow and divide.
The second, our fasting OS, begins in a fasted state and needs at least 12-16 hours to reach its full potential. Without having to focus on digestion and absorption of nutrients, the body can concentrate on cleaning and maintenance, aka cellular autophagy.
The two OS systems are equally important; our bodies need maintenance between stretches of extended use. We need to provide sufficient time for both operating systems to work – something that isn’t possible when we eat too frequently.
But doesn’t fasting burn muscle?
A common concern with fasting is that the body will start to break down muscle. In a state of low blood sugar, the common misconception is that muscles will break down proteins and turn them into sugar. While this process is ongoing to a small degree, fasting does not accelerate it.
Researchers have analyzed the utilization of different fuels during an extended fast. If we break down the data presented, taken from Dr. Kevin Hall’s ‘Comparative Physiology of Fasting, Starvation, and Food Limitation’, we can quickly dispel the ‘fasting burns muscle’ notion.
Before starting a fast, the body relies primarily on carbohydrates. After a few hours of fasting, the body’s carbohydrate use drops dramatically as we use up much of our liver glycogen stores. Simultaneously, our fat metabolism rises sharply to compensate for this carb decline. But look carefully at the blue line representing protein (insert image). At no point during a fast does protein metabolism increase; it actually does the opposite.
Instead of burning protein, our muscles and other tissues conserve it. That’s because proteins and the amino acids that make them up are critical to almost every action of the cell. Even in a state of starvation, it is vital to conserve protein, especially when there is fat that can be used. As a result, our rate of protein metabolism drops when we are fasting so as to preserve these critical molecules.
Besides helping us out when there isn’t enough food around, what other purposes do our fat stores serve? For millions of years, animals have adapted to store away food for later. Just look at bears or squirrels preparing for hibernation. We have retained the ability to store fat but seem to have forgotten that we’re also supposed to use it.
With this brief understanding of what happens in the fasted state, let's look at the benefits of TRF.
TRF reduces fat mass without affecting lean mass
TRF has repeatedly been shown to reduce fat mass without altering the level of lean mass, even when animals on a TRF diet eat the same total daily number of calories as those given 24-hour access to food (Manoogian)(Chaix). Also, when compared to a calorie-restricted diet, TRF has the same effect of reducing total fat mass, but it doesn’t drop the total weight to the same degree as CR, illustrating its conservation of lean muscle mass.
When we fast for 12-16 hours we allow our glycogen stores to run low. The body counters by burning some of its stored fat. When we expose the body to these conditions on a regular basis we become more adept at using stored fat, resulting in less hunger and improved energy levels. This understanding is a major breakthrough in nutrition science, which has long focused on simply restricting calories to achieve weight loss. Attempting to be chronically hungry is very difficult when we are surrounded by food.
By simply restricting our time window for consumption we may be able to maintain enough dietary pleasures and shed fat at the same time. What’s interesting about this research is that there is a direct correlation between the length of fast and the degree of fat loss has been found; longer daily fasts equals greater fat loss.
TRF improves insulin resistance and lowers blood glucose
Type II diabetes is a metabolic disease characterized by high blood sugar and insulin resistance. Insulin is a hormone produced by specialized cells in the pancreas that regulates the concentration of sugar in the blood. This hormone notifies muscle and fat cells when there is too much sugar in the blood, causing them to pull it into the cells. After enough glucose has been absorbed, insulin release tails off so as to keep blood sugar levels from dropping too low.
In Type II diabetics, chronically high levels of blood glucose caused by diet and insufficient exercise leads to a chronic release of insulin in an attempt to offset the imbalance. However, the receptor that insulin binds to in muscles can become resistant to its effects. This is caused in part by high levels of fat in the blood, commonly seen in overweight/obese individuals. This inhibition is a complex pathway; fats bind to a specific enzyme, which in turn modifies the target of insulin receptors. These modifications are harmful as they shut down the signal sent from insulin. In short, insulin and fatty acids indirectly compete for the same pathway. Too much fat in the blood (due to excess caloric intake and inactivity) shuts down insulin, leading to insulin resistance and elevated blood glucose.
With an understanding of how TRF can reduce total body fat, it would logically follow that it would also help to improve insulin sensitivity. Enhanced fat utilization as fuel improves insulin sensitivity, lowering blood glucose levels back to a healthy range.
This is corroborated by the finding that IF (both ADF and TRF) can prevent, and even cure Type II Diabetes in rodent models. Other researchers have observed the same benefits of TRF, with rats exhibiting lower levels of cholesterol, triglycerides, glucose, and insulin resistance. To provoke insulin resistance, rats were given access to food 24 h/day for an extended period, after which they were switched to an 8-hour feeding window. Interestingly, the number of calories eaten by the rats didn’t change when their eating window was shortened. This means the observed benefits had nothing to with food deprivation. The same improvements in insulin sensitivity have also been confirmed in human trials of TRF.
By frequently shortening your feeding window and lengthening your fast, you train your body to burn fat. When you make this switch there are numerous short and long term benefits. In the short term, your energy levels improve and fluctuate less. Food becomes less of a distraction and your body learns to tell you when it is truly hungry and not just craving a sugary snack. In the long term, increasing fat utilization means there is less body fat stored away and less fat floating around in the blood. With less fat circulating, insulin sensitivity remains intact and Type II diabetes can be prevented.
Where does testing need to go from here?
The next stage towards the validation of TRF as a valuable approach to treating obesity and Type II Diabetes requires long-term human trials with a large number of participants. Even though the evidence is encouragingly positive it may be decades before there is unanimous support from the scientific community for the use of TRF. There are so many variables to control for, including age, gender, type of diet (macronutrient distribution), and level of exercise, just to name a few. The length of fast is another variable of interest; how long does one need to fast each day to get the full benefits?
Metabolic diseases are not the only area of interest in the field of fasting. A topic for another time is the emerging evidence for the improvement of cognitive function with various kinds of fasting. It has also shown potential to lower cancer risk and inflammation, improve recovery from exercise, and slow the ageing process. By providing our bodies with a steady cycle between feeding and repair it’s quite possible that TRF acts on many different aspects of our health.