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You may be considering fasting as a New Year’s resolution. Fact is, fasting has been around for ages and is practiced for numerous reasons. It is defined as “the abstinence from food and drink, or both for a lengthy or short duration of time”. Being a regular practice in about every major religion, fasting is most commonly associated with being a religious practice. But aside from this, people also fast for numerous health reasons. These can range from supporting heart health and weight loss to boosting muscle growth and detoxing.  Fasting has even been associated with longevity.

The difference between fasting and dieting

Before we explore the side effects that may arise from it, it is important to note that although it may be done for physical reasons, fasting is not dieting. Unlike dieting, which focuses on trimming calories or cutting off a certain food, fasting focuses on cutting back on food for a period of time, or not eating at all.

So with this in mind, how long is too long to be fasting? When does it stop being beneficial to our physical and mental health, and when should one stop?

Fasting and autophagy

Autophagy (which directly translates to self-eating) is a term that is often associated with fasting and longevity. This is a self-preservation process whereby the body removes dysfunctional cells and recycles parts of them for usage in cellular repair and cleaning. When the body’s cells are deprived of nutrients or damaged, or if there is an absence of external food sources, the body begins to destroy and recycle its own damaged cell bits and proteins to create healthier versions of them.

So as the body’s natural cellular recycling system, it allows the cells to not only disassemble their junk parts but also repurpose the salvageable parts into new, usable cell parts. Its main purpose is to ensure that the body and its cells self-regulate back to optimal, smooth function. 

The link to fasting

Now, how does autophagy link to fasting?

According to a 2019 crossover study, fasting can induce autophagy. In this study, researchers studied numerous indicators of longevity, including the level of autophagy genes in the subjects. 11 overweight adults followed an early time-restricted feeding schedule (which is quite similar to intermittent fasting) and a normal eating schedule.

The early-time restricted feeding schedule resulted in improved longevity incomes, which included autophagy gene (LC3A) production increasing by 22% in four days. 

This basically tells us that if you stop eating for a certain period of time, or significantly lower your calorie intake through fasting, it deprives the body of nutrients, which forces it to repurpose cells in order to function. In fact, a 10-40% reduction in overall calorie intake is one of the most effective ways to induce autophagy, with it occurring within 18 – 96 hours. 


Another term that is mentioned regularly when it comes to fasting and lifestyle changes is ketosis. Autophagy isn’t the only bodily process induced by fasting. When you fast, your body goes through a process of ketosis.

Ketosis is the process whereby your body doesn’t have enough carbohydrates to burn for energy, so it burns body fat instead, leading to the formation of ketones, used for fuel. Through this process, the body begins to lose essential electrolytes such as sodium, magnesium, potassium, and calcium. When this happens for an extended period of time, it can lead to unpleasant side effects. This can then make fasting a health risk if not done correctly.  

The loss of electrolytes

The first risk that arises because of this is electrolyte imbalance. Sodium is responsible for regulating the amount of water found around your cells, magnesium helps support a healthy immune system (amongst over 300 biochemical reactions in the body), potassium maintains normal fluid levels inside our cells and calcium plays an important role in healthy bones, teeth, and a regulated heart rhythm. 


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This electrolyte imbalance leads to side effects, including confusion and irritability, fatigue, headaches, an irregular heart rate, muscle cramps, severe weakness, and nausea.


Prolonged fasting can cause dehydration too. As you get approximately 20% of your daily fluid needs through food, not eating lowers your water intake. This can be very dangerous as frequent or prolonged dehydration can lead to an increase in urinary tract infections and kidney stones. It is therefore recommended that you drink at least two to three liters of water per day during a fast to supplement the loss of water gained from foods.  In addition to drinking water, you should also consider using hydration drops to help maintain your electrolyte balance and stay properly hydrated during prolonged fasting.

How do I start my fast?

Preparation is important when it comes to beginning your fast. The steps you are advised to take by medical professionals include:

  1. Eating moderate quantities prior to fasting: This will get your body used to having limited calorie intake
  2. Reduce coffee intake: Caffeine content whilst fasting leads to pounding headaches and intense dehydration
  3. Stock up on nutrient-filled foods: This will ensure that your electrolyte content is enough to sustain you for the period of your fast. It is suggested that eating foods such as fruits, vegetables, and lean protein provides your body with fiber to help you feel fuller for longer and offer your body more vitamins and minerals.
  4. Stay away from certain foods: Although fats are essential for our diets, consuming the wrong kinds of fats (such as fried foods) can lead to inflammation, aggravated acid reflux, and increased calorie intake, which will lead to weight gain.
    Also, foods that are high in sugar content rapidly increase your blood sugar levels which causes a large release of insulin, which will leave you more tired during your fast, making it more dangerous. 

A pinch of salt a day helps keep the side effects away

You need to ensure your electrolytes are being replenished. This can be done by adding a small amount of salt to the water that you drink. It is commonly known that salt contains sodium, but it also contains amounts of potassium, magnesium, and calcium, which will assist in increasing your electrolyte level. 

The safe ways to fast

You can’t discuss fasting without mentioning intermittent fasting. Rising in popularity over the past decade, intermittent fasting is defined as an eating pattern whereby you seize calorie consumption for an extended period of time (usually between 12-40 hours). When fasting, a healthy meal plan focused on nutrient-dense foods should be followed to make the most of your eating window. There are 4 main eating patterns one can use to incorporate intermittent fasting into their lifestyle, namely:

  1. Time-Restricted fasting: Fasting for 12 hours, eating for 12 hours. This fasting model is recommended for beginners as food intake is not completely restricted. 
  2. The 5:2 Diet: Eating normally for 5 days of the week and restricting calorie intake for the remaining 2 days. With this fasting model, it is advised that you give yourself a one-day break before continuing your fast. This will provide your body with enough time to recover. 
  3. Alternate-day Fasting: Fasting every other day according to individual preferences. It is advised that the food consumed on fasting days should provide at least 500 calories, and this model is not recommended for beginners.   
  4. Eat-Stop-Eat: Fasting for 24 hours once or twice a week. This model is the most straining and can take a toll on your physical and mental health. If you embark on this fast, it is advised that it is done under medical supervision. Even so, experts recommend the 12/16 hour fasting methods instead.

What if I’m on chronic medication?

We need to take into account that chronic medication usually needs to be taken with food, so in this instance, one would need to adjust a fasting regimen to accommodate eating when medication needs to be taken.

Also, fasting can aggravate certain conditions. These include decompensating hyperthyroidism, epilepsy, type 1 diabetes, low blood pressure (as fasting plays a role in lowering blood pressure), and multiple sclerosis.

These conditions are not compatible with fasting as they can lead to hypoglycemia and gastric ulcer attacks. Thus, your best bet would be to consult your doctor prior to embarking on your fast to ensure your health and well-being are preserved. 

How long should you fast for?

This is dependent on the kind of fast you are doing, but most regimens suggest short fasting periods that last 8-24 hours to ensure that health problems don’t arise. However, many people opt to undertake longer fasts of 48-72 hours, and these are considered “Prolonged Fasts”.

Health specialists advise that 48-hour fasts should only be embarked on once or twice a month, never more, and that preparation is prioritized. You’ll need to ensure that you have enough electrolytes because this form of fasting can take a physical toll and will take time to get used to.

Before you start any fast, if you have any underlying medical conditions you should discuss it with your health professional. 

When should you stop your fast?

Nausea is a key indicator of this. If you begin to feel nauseous during a fast, it is advised that you end it immediately.

Nausea typically occurs when your body is too dehydrated. This means that your electrolytes have become too depleted or the ketone body’s concentration in your blood has become too high. Along with this, fatigue, loss of focus, increased anxiety, intense headaches and dizziness are other indicators that you should stop the fast.  

Can fasting become a way of life, and not just an occasional thing?

“… fasting isn’t a ‘starvation’ diet, it’s a healthy lifestyle”.

These are the words of Mayo Oshin, who has been doing intermittent fasting for over 4 years now. Clinical research indicates that long-term calorie restriction (specifically, between 3-15 years) has been shown to increase autophagy. It’s also been shown to increase the number of molecules involved in removing dysfunctional cells. So yes, fasting can most definitely be incorporated into your lifestyle.  

Can fasting impact your sleep?

If done correctly, fasting can increase the production of orexin-A, a neurotransmitter that is linked to alertness. People who fast have been shown to have lower orexin-A levels at night, and higher levels during the day. This results in them being more alert during the day and more restful at night.

However, fasting can also impact your sleep in a negative way. This will depend on the time of your meals (irregular meal times disrupt sleep patterns).

Fasting can also lead to a decrease in melatonin, the sleep hormone which plays a massive role in sleep patterns. Along with this, it can also lead to a spike in cortisol, the hormone associated with stress. Too much of it can reduce sleep quality and make falling asleep difficult. 

The best way to prevent this spike is to ensure that you eat balanced meals during your non-fasting time. You should also make sure to consume enough calories to keep you energized and mentally sharp. 


Fasting isn’t just done for weight loss. Along with religious reasons, fasting is done to improve longevity. This is done by improving metabolic functions, lower blood sugar levels, delaying aging, lowering cholesterol, reducing inflammation, and improving cognitive performance.

It can be very beneficial to your health and well-being if done the right way. So, use the steps provided above, and consult with your doctor to find the best fasting model for you.  


  • Johnstone, A., 2015. Fasting for weight loss: an effective strategy or latest dieting trend?. International Journal of Obesity, 39(5), pp.727-733.
  • Welton, S., Minty, R., O’Driscoll, T., Willms, H., Poirier, D., Madden, S. and Kelly, L., 2020. Intermittent fasting and weight loss: Systematic review. Canadian Family Physician, 66(2), pp.117-120.
  • Santos, H.O. and Macedo, R.C., 2018. Impact of intermittent fasting on the lipid profile: Assessment associated with diet and weight loss. Clinical nutrition ESPEN, 24, pp.14-21.  
Bongane Nxumalo

Bongane Nxumalo

As a recent graduate of Rhodes University, Bongane is skilled in content production and editing for Print Media, Digital Media, and On-Air Content. With an interest in Current Affairs, Entertainment, and Politics, Bongane is able to provide a vast range of content that is relevant, informative, educational, and entertaining.


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