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Fasting While Sick: Is It Safe, and Does It Help You Heal?

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Kasparas Aleknavičius, MD December 28, 2022
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When you’re having a common cold, the last thing on your mind might be consuming a large meal. However, there are times when a hot chicken soup sounds delicious while struggling with the flu. Either way, losing appetite as well as having cravings is completely normal.

The important question is – to eat or not to eat? Does your body need to starve to heal, or does it need fuel? Can intermittent fasting help you manage cold and flu symptoms?

We’ll dive into the topic in this article.

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Does Fasting Help When You Are Sick?

There is only limited evidence that fasting can help when you are sick. Nonetheless, considering the overall benefits of intermittent fasting, some form of it can have potential benefits for healing.

During fasting, the body uses fat as fuel instead of glucose and produces ketones. One study done on mice found that ketones can protect from bacterial inflammation.

Also, there are some possible other benefits to fasting that can go hand in hand with healing a sickness.

Fasting is defined as abstaining from food for a predetermined amount of time. It cleanses your body of toxins and drives cells into functions that are not normally activated when there is a constant supply of the energy needed from food intake.

Fasting has an anti-inflammatory effect, reduces oxidative stress, increases autophagy, and improves blood glucose levels, and blood, pressure. Moreover, it can also influence the production of immune cells.

The effects on the immune system may depend on the type of fasting. For instance, the 12-hour intermittent fasting routine is the easiest type of fast that can reduce inflammation in the body.

More advanced routines such as a 24-hour fast can help manage cholesterol and sugar levels, and reduce inflammation.

4 Ways Fasting Helps the Immune System

Being constantly sick can initially be caused from a weakened immune system. Here are some ways fasting affects your immune system.

1. Decrease inflammation

When you are sick, your immune system sends white blood cells to assist in the fight against bacteria or viruses. When there is a chronic inflammatory response, the blood cells attack healthy tissues and organs as well.

These health conditions can result in a number of diseases such as diabetes.

Monocytes are inflammatory immune cells that can be harmful to your body. Intermittent fasting reduces the release of these cells in blood circulation.

Moreover, fasting for 24 hours or more can reduce oxidative stress in cells, and therefore, reduce inflammation, and help fight viral infections.

Viral inflammation can impair the immune system. This means that intermittent fasting can help strengthen your immune response by reducing inflammation, which may also aid in your recovery from illness.

2. Increases immune cell production

Immune cell production is a process that activates the immune system in order to fight bacterial and viral infections by changing the rates at which immune cells and proteins are created.

Fasting cycles decrease inflammation and stimulate lymphocyte-dependent cancer cell-killing processes. Moreover, fasting and refeeding cycles have been found to increase hematopoietic stem cell activation and immune cell rebuilding.

Therefore, intermittent fasting increases immune cell production which then plays an important role in the body’s resistance to bacterial infections and then promote healing.

3. Lowers insulin levels

Lowering insulin levels releases stored blood  sugar, making energy accessible at all times. Insulin regulates glucose in your body. Reducing insulin resistance also helps prevent type 2 diabetes.

Obesity and type 2 diabetes are associated with impaired immune responses to viruses and pathogens. Moreover, a T cell, which is a type of immune cell is located in excess body fat and can have a negative impact on insulin sensitivity.

Intermittent fasting can lower insulin levels as well as blood sugar levels. Therefore, it can help boost your immune system responses and relieve the symptoms of diseases.

4. Promotes autophagy

Autophagy is your body’s way of recycling cells. It reuses old, and damaged cell parts. Moreover, it also manages the quality of cells. It removes nonfunctional cell parts that affect performance, as well as infected cells.

Most importantly, it destroys pathogenic bacteria that damage the cell. Therefore, it can help boost your immune system responses by replacing damaged cells with healthy ones.

Intermittent fasting stimulates autophagy, which promotes the development of new healthy cells and boosts the body’s ability to withstand internal stresses. Besides, calorie restriction has been shown to activate autophagy.

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Fasting Can Also Help You Prevent Chronic Diseases

Intermittent fasting can lead to better metabolic health. The beneficial outcomes are caused by the activation of adaptive cellular stress-response signaling pathways, which improve DNA repair, mitochondrial health, and autophagy.

Here are intermittent fasting benefits for various medical conditions:

  • Faster weight loss – fasting increases your metabolic rate, and helps you lose visceral fat caused by fat stores. Visceral fat can cause metabolic syndrome and obesity.
  • Stable blood sugar levels – intermittent fasting can reduce blood sugar levels, and prevent type 2 diabetes.
  • Improves blood pressure and bad cholesterol levels – reduces heart disease risk factors.
  • May increase the growth of new nerve cells – intermittent fasting benefits brain function and may protect against cognitive decline. Helps prevent Alzheimer’s and Parkinson’s diseases.

Although further research is needed, intermittent fasting can also be useful as an accompanying treatment during chemotherapy of cancer.

How to Fast Safely When You Are Sick

When you’re sick, your body is already vulnerable, so it’s critical to be attentive and fast safely.

Choose the right fasting type

There are numerous fasting types out there. Hence, here are the ones that can have the greatest effects on cold and flu infections, as well as optimal health:

  • 12-hour fast – the easiest type of fast to follow. It helps with cellular repair, turns fat stores into energy and releases ketones into the bloodstream.
  • 16-hour fast – is beneficial for avoiding obesity, diabetes, and liver disease, also results in reduced inflammatory response.
  • Alternate day fasting – is beneficial for hearth health, and can help lose body fat.
  • 24-hour fast (Eat Stop Eat) – the most extreme in this list. This type of fast isn’t for everyone, so make sure to consult a medical profesional before attempting. This type of fast helps cleanse the body, and improve cardiovascular health.

If you’re still having trouble deciding on a fasting plan, you might want to look into the DoFasting app. It’s a customizable application that provides you with a list of the most popular intermittent fasting plans to choose from.

Moreover, it assists you in being consistent with professional tips and tricks as well as informative articles that will answer your fasting queries, and how fasting affects your body.

It also has a fasting tracker, which might be useful when you’re sick. It will remind you when your eating or fasting windows open or close, allowing you to relax and concentrate on getting better.

Eat the right foods

Certain foods that you consume during your eating window can help strengthen your immune system, and therefore, help you get well sooner.

The best foods to fight a cold:

  • Chicken soup – source of electrolytes, protein, vitamins, and minerals.
  • Citrus fruits – plenty of vitamin C.
  • Ginger – helps to clear congestion and soothe your throat.
  • Garlic – might help prevent colds, has antimicrobial properties.

The best foods to fight the flu:

The best foods to prevent illnesses:

  • Garlic – includes probiotics, phosphorus, zinc, magnesium, potassium and vitamins C, K, Folate, niacin, and thiamine.
  • Onions – high in antioxidants, vitamins and minerals.
  • Yogurt – one of the best source of probiotics.
  • Fruits and veggies with vitamin C.

Therefore, make sure to choose the right food preferences in order to fight bacterial infections.

Stay hydrated

Proper hydration can assist the skin and mucous cell membrane operate as a barrier to prevent bacteria from entering the body while sick. Drinking enough water can also help reduce any discomfort caused by coughing, sneezing, or just breathing.

Besides that, it can help with regulating body temperature, normalizing blood pressure and food digestion.

To specify, women should drink about 11.5 cups of fluids a day, and men should drink 15.5 cups of fluids a day.

In order to stay properly hydrated, you can always have a water bottle next to your bed. Always drink a large cup of water in the morning right after waking up. You can also track your water intake with the DoFasting app, to always be aware of how much water you need to drink.

Who Should Not Fast While Sick?

Even though fasting while sick shows promising results, there are certain people that should avoid doing that.

People with chronic conditions such as diabetes, should not attempt to fast while sick. It can lead to having your blood sugar levels too high and result in diabetic ketoacidosis (DKA).

Also, it can have a negative effect on people that are taking certain medications. Hence, you should also consult their doctor if fasting is compatible with their lifestyle.

All in all, you should always consult wellness professionals if you’re still unsure how healthy it is to fast during an illness.

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Even though there is a saying that you should “feed a cold and starve a fever,” most research does not conclusively establish that intermittent fasting can help when you are sick or that it helps manage flu like symptoms. This isn’t to say you shouldn’t try it if you don’t have an appetite to begin with.

Intermittent fasting can decrease inflammation, promote autophagy, lower insulin levels, and increase immune cell production.

But do make sure to consult a healthcare professional if you have a certain medical conditions, since it can bring some adverse effects.


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Kasparas Aleknavičius, MD
  • Head of Medical Affairs at Kilo Health
  • Medical Doctor at Vilnius University, Lithuania
  • Partnering with the EU-funded Young50 and EUPAP projects

Kasparas Aleknavicius is a medical doctor that graduated from Vilnius University, working as head of medical affairs at Kilo Health. After nearly 5 years in the industry, Kasparas focuses on digital health and is looking for innovative ways to help people lead healthy lifestyles through digital health and wellness platforms.

You can find Kasparas on LinkedIn and follow his latest research on Medium.

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