Your metabolism is the process by which your makes and burns energy from food and fat reserves. You rely on your metabolism to breathe, think, digest, circulate blood, keep warm in the cold, and stay cool in the heat: everything you do is accomplished with metabolic aid.
It is widely believed that ‘boosting’ your metabolism can bring about more rapid weight loss and improved muscle gains. This is true, to a point: the issue is that any method used to improve your metabolic rate will elicit quite a slight effect. Your basal metabolic rate (BMR) has more to do with your weight, height and gender than anything else.
However, there are some things we can do to slightly increase our metabolic rates, make the digestive process easier and more comfortable, alter the hormonal output of our bodies to make them work better towards our goals, and make sure that we are burning fat where we want to. Top of the list of techniques to achieve these feats is intermittent fasting (IM).
Intermittent fasting, during which you fast for the majority of the time and only eat during a specific, set window, is one of the most popular dietary protocols going. There is good reason for this: there are a great many health benefits to be had from any of the number of different versions of the protocol. However, amongst these benefits- which we will touch on below- one stands head and shoulders above the others in terms of what makes intermittent fasting so alluring and so potent: it can drastically improve your metabolism and digestive processes.
The shorthand: it can help you to lose weight more efficiently and recover faster from hard exercise.
How Can It Do This?
There are a couple of mechanisms that underpin the weight loss commonly associated with intermittent fasting. Primarily, there is a time limit as to when you can eat. If you limit the amount of time in which you’re eating, it’s almost inevitable that you take in fewer total calories. Grazing all day long, for 16 hours or so, allows you to eat a lot of unnoticed, unnecessary macronutrients. On the other hand, trying to cram in everything during a 4-hour window will generally cause you to hit your tolerance well below your maintenance caloric need.
Maintaining a caloric deficit will always be more important to weight loss than anything else: ‘boost’ your metabolism as much as you like, but without this deficit you will not lose weight.
In addition to this, stabilised, decreased insulin levels will stop you being so hungry and will stop you from having energy surges and crashes. Boosted Human Growth Hormone (HGH) output will allow you to lose fat whilst maintaining- or even sometimes building- lean muscle mass. Lowered oxidation stress and diminished inflammation will allow you to exercise more, with greater intensity, knowing that you will recover faster than before.
There will also be benefits to be had with regards your gut and digestive health, which will be good in and of themselves, but will also lend themselves to weight loss, muscle gain, and a more comfortable, less bloated appearance and feel.
Overall, these factors should mean that your metabolic rate can be increased by anything from 3-14% on an intermittent fasting protocol (though the lower end of this range is generally more realistic). So, you should be primed for losing weight, and should more easily find yourself in the caloric deficit necessary for doing so.
The Benefits Of Intermittent Fasting
Most people make use of intermittent fasting in order to bring about this weight loss or body recomposition. However, there is far more to IM than this- there are far more benefits to be had from including regular fasting periods in any diet, many of which have a direct impact on metabolic health.
Following an IM protocol can:
- Improve digestion
- Aid gut health
- Reduce insulin resistance
- Protect against diabetes
- Reduce oxidative stress and inflammation in the body
- Promote improved cellular regeneration and repair processes
- Aid in cardiovascular health
- Increase HGH output
These all come as a result of changes in the body’s hormonal output, alongside its ability to fully rest its digestive processes for protracted periods of time. They will all likely come quite naturally to most people who simply change when they eat and when they fast, without having to worry too much about what- or how much- they are eating (though dietary content is, of course, important for long-term health and weight management.)
How Intermittent Fasting Can Lead To Improved Metabolic Health And Weight Loss
Unlike most ‘diets’, intermittent fasting won’t restrict what you eat, unless you choose to follow a protocol in conjunction with another diet plan, like a ketogenic, Mediterranean or calorie-controlled diet. However, intermittent fasting needn’t be about changing what you eat, but rather following a very careful plan that manipulates when you eat.
Intermittent fasting requires you to follow a set pattern of eating: it relies on this pattern, and little else, in order to work. By better scheduling your nutrient intake, you will be able to make the most out of everything that goes into your body, whilst giving your body time to fast. This fast will rest the digestive system for extended periods of time, whilst simultaneously leading to the hormonal and metabolic changes that are beneficial for the loss of body fat.
Intermittent fasting can therefore be a good protocol for weight loss, both because of the science that backs up the protocol itself, and due to the fact that you needn’t worry about counting calories or macronutrients (though you can if you want, and this can be done to great effect.)
Counting calories can be demanding- especially to somebody new to scheduling and maintaining set dietary requirements- and can be dispiriting to those seeking to lose weight long term. Intermittent fasting has the solid virtue of not only being very effective, but also of being incredibly simple and easy to implement.
Large meals are allowed on an intermittent fasting protocol- in fact, they are even required on some versions of it. If you are only eating one meal per day, or only eating within a couple of hours every day, you will need your meals to be large just to get by. However, as these large meals will be accompanied by long periods of fasting, it is quite common for caloric deficits to occur, even if the dieter doesn’t specifically try to maintain one or feel like they are in one.
This period without eating and the caloric deficit that will often result is one reason that IM can be beneficial for metabolic health and weight loss. However, many of the really beneficial aspects of IM as a protocol come from the human biology underpinning the fasted state itself.
The Fasted State
There are a few states through which the body transitions as the feeding cycle takes place, each of which concerns us as they each bring about and represent very different biochemical reactions and roles.
Firstly, the fed state begins at the outset of nutrient intake (eating a meal). It lasts from the beginning of the meal to about 3-5 hours after it is finished. This will be the period in which the body is digesting food, breaking it down and absorbing nutrients. This will be a thermogenic phase, during which energy will be used in the digestive process. However, in the vast majority of cases, more energy will be brought into the body than is used in digestion. Insulin levels will spike as this energy is brought it, and glycogen levels and blood sugar levels will be raised accordingly.
Following on from the fed state, the body goes into the post-absorptive state, which can last until up to 12 hours after the body’s last intake of nutrients. The body will not be digesting food during the post-absorptive state, and insulin levels shouldn’t be too high, but glycogen levels will be raised. This glycogen is the body’s preferred source of energy, and so will be burned off in lieu of body fat. This is why it can be hard to lose weight outside of a fast.
After the post-absorptive state comes the fasted state. This is, perhaps unsurprisingly, the foundation and basis of any intermittent fasting protocol. It will be the period in which all of the biological processes we are looking at today will occur. At this point, a few things occur at the hormonal and cellular levels, which we will look at below. The fasted state typically begins about 12 hours after the last nutrient intake, so can only occur when nothing has been eaten for 12 hours. It will last until the next meal, when the fast is broken.
What This Means
There are two main things that make the fasted state so beneficial for fat loss and improved metabolic health. The first is that insulin levels will be at their lowest. Indeed, as we have noted above, one of the major health benefits of IM is that it usually leads to increased insulin resistance. Blood sugar therefore won’t spike as harshly, and appetite will be more easily and more lastingly sated. Secondly, during the fasted state, body fat will become more readily accessible as an energy source, making it easier to burn.
In addition to these benefits, cells also begin repair processes that are halted by the digestive process, and genes like human growth hormone (HGH) are expressed that aren’t made as readily available as needed, in large enough quantities, when the body is digesting nutrients.
Some of the changes that occur in the body during a fasted state include:
- Insulin sensitivity improves: This is accompanied by a drop in total insulin and blood sugar levels. This can aid in reversing the effects of related diseases like diabetes, alongside making body fat stores more accessible and keeping the appetite stable, even during a caloric deficit or protracted fast.
- HGH levels increase: This will have quite a major impact, especially for those with athletically demanding training regimes. HGH levels can increase by as much as a multiple of five. HGH is crucial for weight loss and hypertrophy, so will be of benefit to athletes and those looking for body recomposition. Improved levels should lead to improved rates of hypertrophy, meaning that more muscle mass should be built for the same caloric intake and training stimulus.
- Cells repair: The digestive process can inhibit some of the body’s much needed cellular repair processes. In the absence of the digestive process, these processes can work optimally. This includes the digestion and removal of dysfunctional, old proteins that build up within cells, and may help you to recover more efficiently from training.
- Gene expression: The function of genes related to protection from chronic disease and the maintenance of longevity is the most positively affected during a fasted state.
These all combine to improve the body’s metabolism and should elicit a more rapid weight loss or muscle gain (or both, as recomposition can be possible on an IM protocol in certain circumstances.) The body will be able to process (burn) visceral body fat rather than using glycogen reserves for energy. This means that fat reserves will be diminished. Alongside this, the increased HGH output will aid in building muscle (hypertrophy) under correct and sufficient stimulus, and with sufficient protein intake. Muscle mass is very metabolically demanding, using up far more calories per pound than fat does, especially when active. This means that improved overall musculature will lead to a heightened caloric demand- a faster metabolic rate. This in turn will make it easier to maintain a caloric deficit, and/or burn greater amounts of fat, hopefully locking you into a virtuous cycle.
Insulin And Intermittent Fasting
Decreased insulin levels will also play a role. Type II diabetes is one of the developed world’s largest problems. One of the disease’s main features is insulin resistance and its attendant high blood sugar levels. Any medication or dietary protocol that can help to lower insulin resistance is therefore a useful tool in protecting against and even reversing type II diabetes.
One of the most important aspects inherent to intermittent fasting, for weight loss and metabolic health, is its ability to reduce insulin resistance. In turn, this can lead to a major reduction in blood sugar levels and can help to fight diabetes. Studies have shown that intermittent fasting can reduce blood sugar by up to 6% and insulin levels by up to 31%. IM may also help to benefit against kidney damage, one of the leading, most severe complications involved with diabetes.
Whilst lowering insulin levels overall comes with its own benefits, it will also aid in losing body fat and maintaining an improved metabolism. High insulin levels lead to excess insulin in the blood stream. Hunger pangs will often occur under such circumstances, and the body will feel hungry out of proportion to its nutritional requirements: your perception of your own hunger will be skewed and inflated, as insulin causes cravings. Getting rid of these pangs will make it far likelier that you will maintain a caloric deficit, leading to weight loss, and it will make the process far more comfortable.
Digestive Health And Intermittent Fasting
There will also be improvements to digestive health under an IM protocol. Some of these benefits come from simply giving the digestive system a break. If somebody suffers from any kind of stomach bile/acid or reflux issues, they will benefit greatly as their stomach’s acid levels are given time to return to normal after digesting. This will help everybody more generally, as pH balances are restored, and acid levels diminished.
Fasting can also aid in treating digestive distress such as IBS, as those suffering from it will spend less time having to deal with it. Periodic fasts will also reduce postprandial endotoxemia, a metabolic risk factor, which has been found to increase the risk of insulin resistance and the likelihood of obesity.
The composition of the gut’s healthy flora and bacteria can also be improved by introducing prolonged fasting periods. Circadian rhythms (the body’s internal timing) play a part here, as gut bacteria also have their own circadian rhythms. Many types of gut flora oscillate activity levels through the day, and many even fluctuate in abundance.
The gut microbe Enterobacter aerogenes serves as a good example. This bacterium is melatonin sensitive (melatonin being the ‘sleep’ hormone.) Enterobacter aerogenes’ main role is in sugar fermentation and gas production. Circadian rhythm disruption, through for example, protracted or late-night eating, can disrupt, damage or even kill Enterobacter aerogenes. This will negatively impact metabolic health as sugar fermentation is impaired.
Intermittent Fasting And Your Metabolism
There is evidence to support the idea that intermittent fasting will boost your metabolism in its own right, not just as a result of possible improvements to hypertrophy and digestion. Rodent studies have found that intermittent fasting reprogrammed metabolic pathways in order to maximise energy gained from food. Fasting can increase adrenaline and noradrenaline hormonal output, both of which enable your body to utilise more body fat- especially visceral fat- for energy. These effects have been found to come into play even at rest, meaning that those going through frequent fasting periods will be burning more body fat just sitting around.
The Timetable Itself
Many of intermittent fasting’s highly prized metabolic and body compositional changes come from the above biological mechanisms. However, as mentioned earlier, one of the key aspects of weight loss, and metabolic health, is average daily caloric load. With the best metabolism in the world, exceeding your daily nutritional needs by 500-1000 calories on a regular basis will see you putting on a lot of weight. With the lowest functioning metabolism in the world, a similar caloric deficit should see you losing weight.
These deficits and surpluses can of course be achieved under almost any dietary protocol. However, maintaining a caloric deficit is often more easily done through intermittent fasting.
In fact, it can be hard to meet basic metabolic needs, let alone maintain a surplus, on an intermittent fasting protocol (though it is by no means impossible). If you have only a few hours daily in which to eat, it can be a difficult job getting in 1,800-2,500 calories (a fair spread of average metabolic demands.)
If you tend not to be too mindful of eating on the go, or if you’re given to snacking, this could be of particular benefit to you. You may find yourself taking in calories without realising it throughout the day, and it doesn’t take you much to push yourself above your metabolic needs. If you eat only a couple of large meals per day, then nothing for the rest, you will find it easier to quite naturally stay within the bounds of your metabolic needs.
There are several different protocols for you to choose from when scheduling your own intermittent fasting routine. They all differ in their structure. However, they also all involve the same base theory: each involves splitting your day- or perhaps your week- into fed and fasting periods. As you fast, you will eat very little, or more often nothing at all.
Some of the more popular protocols include:
- The 16:8 method: This protocol involves restricting food intake to 8 hours in every 24-hour period, so something like 10:00-18:00, or 12:00-20:00. This will be followed by a 16 hour fast.
- Eat-stop-eat: This protocol involves fasting for 24-hour periods, once or twice per week. Food intake will be structured as normal over the other 5 days.
- The 5:2 diet: This protocol involves eating normally 5 days per week but restricting caloric consumption to around 500 for 2 non-consecutive days. This is useful for those in hard training, as they can structure their fast days to coincide with rest days, thus not effecting their training too much.
- The one-meal diet: This protocol involves eating a single, large meal, once per day. It can be hard, as typically around 1,500-2,000 calories will need to be eaten in one sitting, but it gives nearly constant attention to fasting periods.
It is important to note that water should still be drunk as usual, at regular intervals, during both the feeding and fasting timeslots.
So, not only does intermittent fasting improve your metabolic rate, enabling and/or requiring your body to take in marginally more calories, IM protocols will also generally lead to an effortless caloric deficit. This two-pronged attack is incredibly efficient for weight loss, and for maintaining a healthy metabolism through a prolonged cut, during which metabolic rates can generally suffer.