Keto Diet Side Effects: The Ultimate Guide (UPDATED)

You’ve seen how the keto diet helped with your friends’ weight loss journey.

You’ve watched celebrities lose weight because of it. To top it off, lots of experts are talking about this weight loss wonder. And now, you’re ready to go keto! 

But that’s just one side of the story. Before you take the big leap, you should familiarize yourself with the ugly side of keto first.

These are no other than the ketosis diet’s side effects.

What are these? Read on to find out!

Why Keto Side Effects Happen?

The purpose of the ketogenic diet is to switch the body’s energy source from sugar to fats. To do this, the body has to burn all the carbohydrates in your body before it can get started on burning fats, which will cause the weight loss you want.

As your body burns the remaining carbohydrates in your diet, your blood sugar and insulin levels will drop. Once your insulin levels reach the right level, your body will start to burn and convert fat into ketones.

These are the energy sources that will be used in place of ketones. When your body is mainly relying on fats for energy, that’s where ketosis kicks in. (1)

This is the reason why the diet is high in fats and low in carbs.

You’re only allowed to consume only 50 grams of carbohydrates daily.

This amount is far from the normal daily carbohydrate consumption of 225 to 325 grams a day. (2,3)

This drastic reduction of your carbohydrate consumption will come as a shock to your body. Since your body is used to consuming that much carbohydrates, it will start to exhibit withdrawal symptoms, which are more commonly referred to as keto diet side effects.

What are the Negative Effects of Keto Diet?

Along with the weight loss, you will experience with ketosis dieting comes a wide array of side effects that may want to make you give up.

If you’re going to stick to keto diet and experience all of its weight loss benefits, you should be ready for these side effects.

To help you get ready for it and understand what’s happening inside your body during dieting ketosis, we’ve provided all the information you need below.

Please take note that we’ve categorized the side effects based on how common it is to experience them.

Top 5 Very Common Keto Side Effects

1. Frequent Urination

The biggest complaint of starting keto dieters is that they have the urge to go to the bathroom many times in a day to pee. This is nothing serious, but frequent bathroom trips can be bothersome and for you. Moreover, it may leave you feeling confused and worried. 

Why It Happens:

First things first, we just have to tell you that there’s no need for you to worry as it is a body’s natural reaction to all the changes it undergoes. There are three reasons why you may urinate more than usual on a keto diet.

First, it is due to the burning of your glycogen stores. Your body stores 500 mg of carbohydrates in your muscles and liver cells. It is stored in the form of glycogen. When you restrict carbohydrates from your diet, your body will burn through your glycogen stores to get energy. 

The thing is, three to four grams of water are stored in a gram of glycogen. As your body goes through your glycogen stores, and the water molecules get expelled in the process. (4)

Second, it may be due to sodium imbalance. When your body excretes fluids, electrolytes come with it. Sodium is an electrolyte that helps maintain fluid balance by binding to water molecules and retain water inside the body. (5)

Last but not least, it is due to the presence of ketones in your body. Ketones are chemical substances produced by the liver when there isn’t enough insulin in your body, as is when you’re on keto. It has been studies that ketones are osmotically active and may induce a diuretic-like effect in the body. (6)

What You Can Do:

To be honest, there’s nothing you can do to prevent it. That’s just how the body works. 

The best thing you can do is find a way to manage other health problems that may arise because of this side effect. You can do this by increasing your water intake and taking electrolyte supplements. 

2. Keto Flu 

Ahh. We’ll start with the dreaded and most famous side effects of them all— keto flu. Everybody has heard about it. Almost everyone has experienced it. However, not everyone knows why it happens and what to do when it happens.

What is keto flu? It is the term used to collectively call the different symptoms you may feel during your keto diet. It is called as such because the symptoms are similar to that of the flu. Here they are:

  • Headache
  • Irritability
  • Fatigue
  • Dizziness
  • Weakness
  • Poor concentration
  • Muscle soreness
  • Nausea 
  • Vomiting
  • Drowsiness

Why It Happens: 

As mentioned in the first side effect we have tackled, frequent urination will be your body’s response to the sudden drop of insulin levels in your body. While it may cause immediate weight loss, it also leads to loss of water, sodium and other electrolytes which is why you feel the keto flu symptoms. (7)

Let us not forget that you’re abruptly cutting off carbohydrates from your diet when you’ve been using it as your primary energy source. You may consider the keto flu symptoms as your body’s withdrawal symptoms from sugar. (8)

What You Can Do: 

That’s a lot, right? Experiencing all these symptoms at once will surely make you want to throw in the towel. 

Don’t do that because we have good news for you! These symptoms occur only at the start of your diet when ketosis is only starting to kick in. It will only last for a few days to a month or so, depending on how your body works, but it is only short term. 

Also, you can minimize these symptoms by drinking plenty of water, getting some sleep, and making adjustments in your diet plan to replenish the electrolytes and sodium that you’ve lost. 

4. Sugar Cravings

The sugar cravings you’ll feel while on keto is not just mental—it can become physical as well. Here are the symptoms of keto-related sugar cravings:

  • Intense craving for sweet food items and carbohydrate-rich foods like pasta, pizza, and rice.
  • Feeling of depression.
  • Irritability.

Why It Happens:

Sugar stimulates the release of endorphins or what they call the happy hormones.

It also releases dopamine, which is a neurotransmitter associated with cravings. 

Animal studies show that sugar has a risk for withdrawal, just like cocaine and other habit-forming drugs.

That’s why you experience withdrawal symptoms when you cut off sugar when you’re on a keto diet. (11)

What You Can Do:

Carb cravings are heightened and brought about by various triggers. If you want to minimize your cravings or eliminate it, you should address these triggers. You can do this by doing the following:

  • Replace your carbs with protein and fats.
  • Drink lots of water.
  • Get enough sleep.
  • Look for keto-friendly alternatives for what you’re craving.

5. Keto Breath

This is possibly the most embarrassing keto side effect of all. This is different from bad breath as dieters describe it as a fruity smell or a scent similar to that of nail polish remover. They also claim that it is like having a metallic taste.

Why It Happens:

Ketones are the ones responsible for keto breath. The body disposes ketones through urination and exhalation. Acetone, a type of ketone, is the main ingredient of nail polish removers and that’s why keto breath smells similar to it. 

What You Can Do:

Since ketones get expelled through urination too, drinking plenty of water can help flush it. You should also eat less protein since ammonia is a byproduct of protein metabolism. 

Top 4 Common Keto Side Effects

1. Constipation

Most of the adverse effects of keto diets affect your gastrointestinal system. The most significant of which is constipation. 

Why It Happens:

The main reason behind constipation is no other than the lack of fiber in the keto diet. The recommended daily fiber intake is 25 to 30 grams. It can be a bit difficult to hit that amount on a ketogenic diet. (12)

Since it is a low carb diet, you need to cut off your intake of carb-rich food items like starchy veggies, fruits, pulses, and whole grains. Unfortunately, these are also the foods that are excellent sources of fiber.

What You Can Do:

For your information, there are keto-friendly fiber-rich foods. These include broccoli, avocado, artichokes, chia seeds, brussels sprouts, and many more. You should include these in your menu plan. (13)

It is also recommended that you boost your water intake and take fiber supplements to aid in digestion.

2. Diarrhea

Diarrhea would be the last symptom you would think of when you’re on keto. Whenever you change your diet or restrict a particular food group in your diet, there will be an imbalance inside your body. Most often than not, it’s your GI tract that takes the hit.

 Aside from frequent bowel movements and loose stools, keto diet diarrhea  is often accompanied by bloating, abdominal cramping and pain.

Why It Happens:

There are many reasons why you may experience diarrhea while on a keto diet. These include:

High fat diet

One food type that may cause diarrhea is fatty foods. As compared to carbs and protein, fats are a lot more difficult to absorb and digest. When they aren’t properly absorbed, the excess fats go to the colon and are broken into fatty acids. This causes the colon to secrete fluid that causes watery diarrhea. (14)

Artificial sweeteners

Most keto-friendly food items contain artificial sweeteners, especially sugar alcohols. The most common side effect of these sugar alternatives is diarrhea. (15)

Changes in the gut microflora

When your diet changes, the gut microbiome will take a big hit too. This is because the gut bacteria feed in short-chain fatty acids, which can be found in vegetables, fruits, and grains. Unfortunately, most of these are rich in carbohydrates.

What You Can Do:

You should take probiotics or digestive enzyme supplements (lipase) that can help in the digestion of fats. Also, limit your consumption of artificial sweeteners. 

3. Insomnia

Few days into your new diet, you may find yourself tossing and turning all night. Lack of sleep may lead to irritability, brain fog, and other similar keto flu symptoms. 

Why It Happens:

When you eat carbs, the release of endorphins, the hormone responsible for making you happy and relaxed, is stimulated. When you’re on keto, you can’t eat carbs, so the amount of endorphins produced will be reduced. 

Additionally, dieting may cause stress. This may lead to the overproduction of cortisol, the stress hormone, and may prevent you from getting the sleep you need.

What You Can Do:

You should find ways to make your body feel relaxed at night. You can do this by taking a hot shower before going to sleep or diffusing a blend of essential oils in your room. (16)

4. Decreased Athletic Performance

One symptom of the keto flu is fatigue and drowsiness. If you’re an athlete, this may translate to poor athletic performance. (17)

Why It Happens:

The culprit behind the decrease in your athletic performance is the reduction of the glycogen stores in the muscles. It takes time before your body gets used to using fats and ketones as your body’s fuel source, so there will be an energy gap during the early stage of ketosis. 

What You Can Do: 

Fortunately, this effect is short term, and your energy levels will significantly improve after a few weeks. It would be best to take keto supplements that will provide energy support during the first few weeks. 

Top 3 Uncommon Keto Side Effects

1. High Cholesterol Levels

The biggest controversy surrounding the ketogenic diet is its effect on blood cholesterol levels. However, this is considered an uncommon symptom because it can be prevented with the right meal plan.

Why This Happens:

This happens because you’re eating food that is rich in saturated fat. 

What You Can Do:

Try to incorporate more healthy fats in your diet plan. Some great examples are avocado, nuts, flaxseeds, chia seeds, and many more. (18)

2. Hair Loss

A few people experience hair loss or a change in their hair’s condition.

Why This Happens:

When you limit your consumption of carbohydrates, you’ll get fewer nutrients. Some of which are needed for healthy hair. 

What You Can Do:

To get the nutrients your hair needs, take supplements (like vitamin E and biotin). 

3. Disruption in Menstrual Period

Missed periods may affect your fertility and can also increase your risk of osteoporosis. (19)

Why This Happens:

Any changes in diet will put stress on your body and may disrupt your period. The reduction in carbohydrates and calories in your diet may cause a drop in various hormones in your body, which will cause you to miss your period. 

What You Can You Do:

If you missed your period, you should seek medical advice to tweak your diet plan accordingly. 

How Long Do Keto Side Effects Last?

The good news is majority of the effects that we have mentioned are short term. Once you’re done with the keto-adaptation phase, all of these symptoms will diminish. 

How long you can experience these unwanted effects will depend on how long keto adaptation will take. This may vary from one person to another. On average, it will take about 2 to 6 weeks. (20)

Is Keto Safe Long Term?

The medical advice is no. There are plenty of reasons why you shouldn’t do keto long term. (21) What we have talked about are just short term keto side effects. When you do keto long term, you’ll experience a lot of health issues. Possible long term keto effects include increased risk for:

  • Heart disease (22)
  • Reduced physical performance and exercise ability (23)
  • Kidney stones/ Gallbladder problems (24)
  • Vitamin deficiencies
  • Poor gut health (25)
  • High cholesterol levels (26)
  • Pancreatitis (27)

Is it Safe to Do Keto Diet?

As per medical advice, the ketogenic diet is a safe diet to follow. However, it is not a diet that’s sustainable long term. It is only meant to be followed for a short term only. 

There are not enough studies to determine how long you can stay in ketosis safely—some say 6 months while other claims 1 year.

It is recommended that you monitor your health and do bloodwork regularly so you can determine if it is still safe for you to continue with your ketogenic diet.

To prevent the short term and long term impacts of keto diet on your health, it’s recommended that you take a few keto supplements that will give you the nutrition you need while you’re on this restrictive diet. 

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