Cheeseboard with assorted delicacies

The web has been floated with dozens of diets or methods on how to lose weight—in the middle of it recently trending “intermittent fasting”. Different intervals reach from the most common 16/8 over alternate-day fasting to even consecutive periods of 72 hours.

“Breakfast like a king; lunch like a prince; dinner like a pauper.” – or better renounce the king?

What are the real benefits of intermittent fasting, and which behavior or preconditions may lead to fatigue?

History of hunters and gatherers

Thousands of years ago, tribes of hunters and gatherers were living day in and day out. Today, many people assume that the way our ancestors lived is the way to go. However, this is not the case – so at least you can not generalize it.

In fact, cavemen were pretty abundant regarding food and its variety. Of course, the tribes had their regional diet. So the Inuit primarily subsisted on wild animal protein. In contrast, Southern Africans predominantly ate wild plant foods, but by adapting themselves to the environment, they usually did not have to suffer from days without any intake.

Usually, they also had only one meal a day, not three plus multiple snacks in between. The pattern of “three meals a day plus snacks” has no scientific evidence, says Mark Mattson, Ph.D., professor of neuroscience at Johns Hopkins University and former Chief at the National Institute on Aging Intramural Research Program. He is “one of the world’s top experts on the potential cognitive and physical health benefits of intermittent fasting.

This routine is reinforced by society in the 21st century, where people eat large amounts of food and very frequently. It ended up with 46.6% of women and 60.5% of men in Germany being affected by overweight and nearly one-fifth of adults (19%) having obesity from 2019-2020, according to the RKI.

According to WHO statistics, the worldwide obesity rate has almost tripled since 1975, and the number of people with diabetes rose from 108 million in 1980 to 422 million in 2014.

Returning to intermittent fasting, it is logical that our ancestors had fasting periods, so Brianna Stubbs, Ph.D., a scientist at the Buck Institute for Research on Aging, but it occurred only as an exception, i.e., famine.

What is intermittent fasting?

What intermittent fasting suggests is a concept for a diet with periods where/when we solely drink water and periods where it is allowed to eat. The most common model is the 16/8 interval, skipping one meal; different from religious fasting, the intervals and durations can vary depending on personal needs.

That is one thing I truly want to emphasize; there is no correct intermittent fasting per se, but there may be a good option for you.

Benefits and science behind it

1. Weight management and metabolism

First and foremost I want to make clear that intermittent fasting does not aim to reduce the number of calories. It merely shifts your daily intake and should not be mixed with caloric restriction (CR). Latter is defined as a general restriction of caloric intake without leading to malnutrition.

This also has many benefits such as weight loss, “increased longevity in many species, significantly improve[d] multiple cardiovascular risk factors, insulin sensitivity, and mitochondrial function”, if done correctly.

Returning to intermittent fasting, people unintentionally end up eating somewhat less than usual because of the time restriction they experience.

Metabolic syndrome is a combination of metabolic deficiencies like obesity, inulin resistance, hypercholesterolemia (increased cholesterol levels), reduced HDL-cholesterol, and much more. It is “a chief risk factor in the epidemic of type 2 diabetes and cardiovascular diseases in the 21st century”.

Luckily, intermittent fasting regulates blood sugar and insulin and keeps metabolic homeostasis up due to the release of the Human Growth Hormone (HGH).

2. Cardiovascular health

Regarding cardiovascular health, there are plenty of advantages, as mentioned above. In general, you can say that what is good for your metabolism is also good for your heart.

For a better overview, there are three potential mechanisms for how it could influence our cardiovascular system.

  • Oxidative Stress Hypothesis

The CR, due to time restrictions, causes a lower production of free radicals by your mitochondria as well as a lower risk for inflammation recognized by, e.g., tumor necrosis factor-alpha and brain-derived neurotrophic factors.

  • Circadian Rhythm

In a simplified manner, this theory states that the working hours of our organs are dictated by the circadian rhythm. Some organs can not work efficiently at night or in the late afternoon. If you choose your fast regimens in a way that you have daytime meals, you will minimize your tendency for metabolic/cardiovascular diseases.

  • Ketosis

The reason for the improvement in weight and lipids can be explained by the concept of intermittent metabolic switching, which happens during an interval regimen. After 6-8 hours, the induction of the ketogenic state sends signals to utilize the ketone bodies from our fat storage. This leads to a decrease in low-density lipoproteins (LDL) and an increase in high-density lipoproteins (HDL).

3. Increased concentration and memory

During fasting periods, our bodies produce more brain-derived neurotrophic factor, which is the basis for neurogenesis (process of neuron production). At that point, it is our task to work on our brains as we do on our bodies to strengthen the synapsis, connecting the neurons.

Furthermore, a paper published in The American Journal of Medicine (Am J Med) in August 2020 shows potential benefits in slowing the progression of neurodegenerative diseases like Alzheimer’s and Parkinson’s.

4. Boosted energy levels

Why does the decreased energy intake not affect the energy levels throughout the day? That is because of evolution; our bodies found a way to access the as fat restored energy reservoirs to supply our whole organism after they expended the glycogen storage.

That is not all because intermittent fasting increases ketone production, the primary energy source for neurons, making us burst through our lives. Additionally, the time-restricted eating pattern increases the mitochondrial density in neurons supporting an energetically loaded you.

Disadvantages and Risks

1. Hunger and cravings

Talking about side effects, hunger and cravings have to be mentioned. Of course, like with all dietary changes, we need time to get used to it. Therefore, it is not unlikely that you’ll experience similar in the first week. To thwart that sensation, it is crucial how we behave during the day, but more on that later.

2. Headaches

A typically reported symptom of intermittent fasting is headaches. Low blood sugar levels may contribute to “mild” headaches, which are “usually located in the frontal region of the brain”.

If you have headaches anyway, staying away from fasting, at least for that day, might be the better choice.

3. Deprived Sleep

According to a 2020 study, about 213 out of 1422 referred to deprived sleep as the most common side effect. Scientists detected dehydration as a significant cause of fatigue. However, later studies suggest the contrary. They even report that “8-10-h time-restricted feeding improves sleep” based on preliminary results.

4. Dehydration and Malnutrition

Within the first days of a fasting regimen, our bodies lose significant amounts of water and salt. Therefore, we need to replace those fluids and electrolytes, ideally with a proper ratio of electrolytes. Some companies provide exactly those kinds of beverages.

Otherwise, being dehydrated will cause a significant drop in your overall performance. You will feel tired and exhausted, both physically and mentally

Quite similarly, our bodies behave with food. If we do not nourish them correctly, we might suffer from malnutrition in the future. But that is a whole different story. Remember to eat high-density carbohydrates and less processed food that satisfies you over a long period and provides the right ingredients.

Who should stay away?

No matter how beneficial intermittent fasting may be, some groups should avoid this dietary change for safety reasons or talk to a professional healthcare advisor in advance. Especially important it is for:

  • “people who are pregnant or breastfeeding
  • young children and teens
  • older adults who experience weakness
  • people with immunodeficiencies
  • people with current or past eating disorders
  • people with dementia
  • people with a history of a traumatic brain injury or post-concussion syndrome”

Even if you are not represented in these groups, bodies react differently. Therefore, please consider a consultation with a healthcare professional.


In a nutshell, much research about intermittent fasting has recently identified many health benefits. Backed up by science, they outweigh the disadvantages. That is only possible if you take care of balanced nutrition during the daytime and complement it with vitamins or other supplements.

For me personally, I find intermittent fasting very energizing. Depending on my schedule, I practice it about 3-5 times a week as a 16/8 from 6 pm till 10 am (not at the weekend). When I have an exam or competition on that day, I want to ensure my body receives everything it needs, can perform well, and does not depend on any reserves.


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