Evidence Based Nutritional Ketosis

Intermittent Fasting: A Complete Guide

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The most-searched for health trend of 2019, intermittent fasting has gone from an obscure method of weight loss, to mainstream popularity. It touts benefits like faster weight loss, a simplified lifestyle, and even higher levels of human growth hormone. But does intermittent fasting really provide all of these things? Today, we will dive into the answer.

The Definition Of Intermittent Fasting

Intermittent fasting can be thought of in relatively simple terms. Any time you stop eating, you’re technically intermittently fasting. If you eat at 5PM, go to sleep, and don’t eat breakfast until 5AM – congratulations, you’ve technically intermittent fasted for 12 hours. However, once you get beyond this overly simplistic definition, there are many more nuances to understand about intermittent fasting.

Unlike most diets or dietary approaches, intermittent fasting does not tell you what foods to eat, but rather, when not to eat. This shift to timing, rather than a list of foods, is part of what has caught the public’s eye. Instead of the usual ‘eat this, not that’ – intermittent fasting allows the dieter a measure of control over how they wish to eat. Want to skip breakfast tomorrow? Intermittent fasting allows you to. Want to not eat for an entire day? You can simply perform a 24 hour fast.

Of course, beyond this, there are many highly structured ways to partake in intermittent fasting. Perhaps the most popular, is 16/8 intermittent fasting. This method is employed by eating all meals within an 8 hour window, and fasting for the remaining 16 hours of the day. Once you have gone a few hours without eating, your body starts to undergo a variety of cellular and metabolic changes.

In fact, this pattern of consumption, followed by periods of eating nothing, is very similar to how our ancestors evolved. Since they were foraging for their own food, it was not uncommon for our ancestors to go 24 hours (or more) without food. It is assumed this is where the scientific mechanisms behind intermittent fasting come from. Interestingly, scientists also surmise that the ability to produce our own energy, without carbohydrate intake, came from this same evolutionary need. The keto diet employs this scientific process, as ketone bodies are manufactured from stored fatty acids, so we can survive periods of carbohydrate scarcity.

Rather than starving to death, our bodies adapted to the lack of food available, and actually thrived in this environment. Our cells not only adjust their hormone levels, but there are actual changes in genetic expression, which occur when you start fasting. Intermittent fasting also lowers insulin levels, and actually raises the level of growth hormone inside your body. Who knew this much would happen, just by skipping breakfast?

Different Types Of Intermittent Fasting

As already mentioned, the most popular method of intermittent fasting is the 16/8 method. This method is most popular, largely due to its ease of implementation. By simply skipping breakfast, you can partake in a 16 hour fast. This is because you will not have eaten anything since the night before, which – depending exactly when you finished dinner – could mean you’ve gone as long as 19 hours, without eating. The 16/8 method can be employed as often as you like, though most don’t recommend fasting more than two to three times per week.

Another popular type of intermittent fasting is the 5/2 method. This essentially boils down to barely eating on 2 days of the week, and eating normally during the other 5 days. On the 2 days of fasting, it is generally recommended to consume no more than 500-600 calories. As you can tell, this is a more aggressive way of intermittent fasting, as you are eating roughly only 30% of your required calories, for two entire days of the week. If you are a novice to intermittent fasting, it’s generally not recommended to start with the 5/2 method.

Another popular method of intermittent fasting is the ‘eat-stop-eat’ method. This is an even more advanced approach, which sees the dieter fasting for 24 straight hours. This can be done once or twice per week, as more fasting than this, is not recommended. This method of fasting is both the most difficult, and simultaneously – the most rewarding. Your body undergoes the most beneficial scientific changes when you fast for 24 hours, as opposed to shorter bursts, like 12 or 16 hours.

Regardless of which of the three methods you choose, intermittent fasting should lead to reliable weight loss. This is, of course, assuming you do not consume extra calories during the eating windows. Another common misconception, is that you can eat whatever you want, when you’re not fasting. This is absolutely not true, and often will lead to weight gain, rather than weight loss. You should still follow all standard dietary guidelines, when partaking in intermittent fasting.

The Science Behind Intermittent Fasting

Intermittent fasting has gotten a lot of press, for the myriad number of scientific changes that occur during the process. Several interesting things happen, both on a cellular and molecular level, when you begin intermittent fasting. For example, your cells begin a repair process called autophagy. Old proteins are removed and recycled during this process, and in fact, scientific studies have shown that this process may be associated with anti-aging benefits. Much like the process of regular exercise, your body repairs itself during intermittent fasting. Interestingly, by eating less frequently, you actually reap rewards that one would think would be associated with eating regular meals.

Another interesting benefit of intermittent fasting, is the huge spike in HGH, or human growth hormone. HGH is prescribed for those with low testosterone levels, so by intermittent fasting regularly, you are essentially getting a nice boost of testosterone, without having to fill a prescription. HGH is also closely linked with muscle building, so intermittent fasting can actually be a beneficial part of a mass gaining program. By eating well, with plenty of protein, performing regular weight training, and partaking in intermittent fasting – you can maximize your physique. There are also a whole host of benefits associated with increases in HGH. Better speed in healing from injuries, an improved overall metabolism, and greater fat burning capabilities, are just three of the benefits associated with higher levels of HGH. Scientists estimate that there is as much as a 500% increase in HGH levels, when you partake in intermittent fasting.

Some researchers also have seen purging of cells related to cancer, during the intermittent fasting process. While there needs to be more research performed in this area, the idea that an uptick in cellular autophagy may help to prevent certain diseases, makes scientific sense. If you’re following a keto diet, you will also be interested to know that fasting rapidly puts you into the metabolically advantageous state known as ketosis. In fact, fasting puts you into ketosis faster than any other method, and your body quickly starts to dip into fat stores, leading to enhanced weight loss.

When you fast, you also alter your gene expression. This process has been associated with increased longevity, which means that intermittent fasting may have a positive impact on aging outcomes. Then, of course, there is the increase in insulin sensitivity. Those with diabetes or blood sugar issues, may wish to try some of the lighter forms of fasting, provided they clear it with their doctor first. There have also been neuroprotective benefits associated with intermittent fasting, as well as decreases in oxidative stress and inflammation.

Intermittent Fasting And The Keto Diet

You can easily combine intermittent fasting and the keto diet, to achieve maximum fat burning results. Since fasting helps avoid the dreaded keto flu, as well as shifting you almost instantly into ketosis, they are a great tag team. You will also find it’s easier to fast for longer periods of time when you are consuming a keto diet, since you are used to producing ketones, and living without carbohydrates. If you consume a keto diet around your intermittent fasting, you will also provide your body with fat to use as fuel during the fast, which will keep your brain in peak condition. Rather than feeling sluggish and tired, which is how many feel when they attempt fasting with a high-carb diet, you will feel energized and focused. This is all due to the interesting biomechanics of the ketogenic diet.

As you take in more fats (especially medium-chain fatty acids, like those found in coconut oil), your brain will begin to function at its peak capacity. This change in performance can be seen anecdotally, when we compare it with the sluggishness that is common after consuming a sugary snack. Once the initial sugar rush wears off, you’re left feeling foggy and subdued. The keto diet provides the complete opposite of this – it allows your brain to fire on all cylinders, and gives you steady, long-lasting energy. When you combine the keto diet with intermittent fasting, you’re able to take advantage of the neurological benefits of both approaches, which lets your brain operate at its fullest capacity.

Does Intermittent Fasting Boost Your Ketone Levels?

As you follow a ketogenic diet, your output of ketones steadily increases. When you are consuming a high-carb diet, your body and brain rely on glucose for energy. In layman’s terms, this means your intake of carbohydrates is your main fuel source. Since the keto diet eschews carbohydrates, your body is forced to find another energy source. Interestingly, it actually starts to create its own energy supply, via the production of ketones. Your liver breaks down fatty acids, in a process called beta-oxidation. This is where your energy now comes from, if you’re following a keto diet.

This production of ketones can also occur from fasting – especially longer fasts. That’s right, you don’t have to be following a ketogenic diet to produce ketones – intermittent fasting alone can invoke ketone production. But if you are already following a keto diet, you will already be producing ketones – meaning intermittent fasting on top, will cause even higher levels of ketones. This deep level of ketosis will show up on our ketone breath monitor, where you can see exactly how many ketones your body is producing.

This deeper level of ketosis is also crucial for enhanced weight loss, as well as improved cognitive functioning. Scientific studies have shown great correlation between higher levels of ketone production, and enhanced fat loss, amongst other physiological processes. It makes sense – if you’re going to be running off ketones, you want the highest amount possible circulating in your body. When you combine the keto diet with intermittent fasting, you can maximize the internal production of ketones. You also optimize your cognitive function, and maximize your weight loss, when you marry together the keto diet and intermittent fasting.

In Conclusion…

Intermittent fasting and the keto diet have taken the world by storm. Nearly 2 million people per month search for information about the keto diet, and combined with intermittent fasting, it is the most popular nutritional approach in the world. Unlike a traditional western diet, ketogenic diets rely on ketone bodies, rather than glucose. Since keto dieters eschew carbohydrates completely, they don’t have a steady supply of glucose, or good amounts of glycogen stored. Therefore, they must rely on an alternative fuel source. This alternative fuel source is ketones, which are made by your liver. Taking fat and converting it into energy, is called beta-oxidation.

Much like diabetics who track their blood sugar levels throughout the day, keto dieters like to track their ketone levels. Traditionally, this has been a difficult task, as the existing options were less than optimal. You could use ketone urine testing strips, or prick your finger multiple times a day, and use a ketone blood test. But as we’ve shown, the best way to test your ketone levels – especially multiple times a day – is using our patented, clinically-backed ketone breath monitor.


Casey Thaler, NASM-CPT, FNS

Casey is one of the most highly-regarded voices in the paleo and keto communities. He has written over 200 articles on health, science, nutrition, and fitness. As a National Academy of Sports Medicine certified personal trainer and fitness nutrition specialist, he has also helped thousands of people lose weight, look younger, and live their healthiest lives. He is also the author of the best-selling title, The Essential Instant Pot Keto Cookbook.

Comments (2)

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    June 12, 2020 Reply

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