What Are the Side Effects of a Low Carb Diet?

Parul Dube

August 11, 2023

Everyone’s definition of a low-carb diet is different. Many people, for example, eat more carbohydrates than their bodies require, and cutting back on carbohydrates can help them return to healthy carbohydrate consumption. However, others prefer to reduce carbohydrates even further to control their glucose levels better or lose weight. Carbohydrate provides energy to the body. The recent guidelines recommend that around 45 to 65% of an individual’s daily calorie consumption should be met by consuming carbohydrates. So, completely eliminating it from your daily diet is an absolute no. 

While carbohydrate restriction isn’t required to lose weight, sometimes people would prefer to do so since it expedites the process. Fewer carbohydrates means fewer calories.  However, the ideal diet for you would be the one you can follow for a long time or that allows you to improve your health.

Your body will take time to adjust to a new diet. So, it is essential to consult with a qualified nutritionist before adopting a low carbohydrate diet. 

Reducing your carb intake, particularly unhealthy simple carbs from refined grains and sugar, can have beneficial effects. However, you may experience low-carb side effects depending on how many carbs you cut out. These can be uncomfortable but typically subside as your body adapts after the first week or two.

An Introduction of Low Carb Diet

A low-carb diet is where between 20-30% of your overall daily energy intake comes from carbs. It comes in a few varieties. Some people adopt 100 to 150 grams of carbs per day, while others approach a more considerable reduction of between 50 and 100 grams.

Following a lower-carbohydrate diet means reducing the intake of foods containing carbs and not eliminating them. It’s important to note that you have to increase the amount of protein and fat while decreasing the carb intake. 

6 Side Effects of a Low Carb Diet

Here are the most prevalent adverse side effects of low-carb diets.

1. Constipation

Constipation is a common complaint among those on a low carbohydrate diet, especially very low carbohydrate diets like keto. While any change in your usual dietary patterns can cause changes in your bowel movements, constipation is common among those on a low carbohydrate diet.

One cause for constipation is a lack of fibre from low-carb diets’ avoidance of high-fibre foods like beans and grains, which are also relatively high in carbs and so generally avoided on low-carb diets.

While constipation can often go away as the body adjusts, staying hydrated, taking a fibre supplement, and eating more low-carb, high-fibre foods can help. Choose foods like broccoli, cauliflower, chia seeds, avocado and coconut, which are some of the high fibre- low carb foods. However, consult a healthcare provider if constipation persists.

2. Fatigue

Because carbs are the body’s primary fuel source, being tired all the time is a common symptom of low-carb diets. In addition, a study suggests that limiting carbs to less than what our bodies require for healthy energy can cause weariness, mainly as the body adjusts to the diet plan. 

Low-calorie diets paired with low-carb foods, in general, can cause weariness, so make sure you’re getting enough calories to maintain your lifestyle.

To lose weight, you’ll need to eat fewer calories than you burn. However, a calorie deficit that is too high will reduce your daily energy expenditures and slow your metabolism. 

3. Headaches

If you cut back on carbohydrates, you’ll also cut back on sugar. Withdrawal symptoms such as headaches might occur in those habituated to eating more sugar. In addition, various studies suggest that when you start a low-carbohydrate diet, the severity of your headaches increases.

4. Muscle Cramps

Muscle cramps can occur if you don’t get essential minerals in your diet, such as magnesium and potassium. Potassium, salt, and magnesium can regulate muscle contraction and several other important activities related to nerve and muscle function.

Whole grains are a good source of such minerals, and cutting them out of your diet may cause deficits and adverse effects. Because carbohydrates interact with water and glycogen storage, lowering carbohydrates forces your body to carry less water. Therefore, you may lose these minerals due to a significant loss of body water.

Some of the low carb foods, which are high in potassium are zucchini, spinach, mushroom, cauliflower, beetroot etc. Salmon is also a good source of potassium. 

5. Bad Breath

Low-carbohydrate diets are frequently associated with bad breath (halitosis). A bad taste in the mouth sometimes accompanies terrible breath.

In the lack of preferred glycogen, your body resorts to ketone for fuel on low-carb diets. Ketones are eliminated by urination and exhaling. Therefore, ketone exhalation could be the source of bad breath.

6. Low Athletic Performance 

Low-carbohydrate diets don’t give much in the form of glycogen stored energy, which is the body’s preferred energy source for activity. As a result, your capacity to perform during exercise, sport, and training activities will decline.

A study shows that participants performed worse on high-intensity cycling and running tasks after four days on a ketogenic diet than those who’d spent four days on a high-carb diet. 


The adverse effects you may experience while on a low-carb diet are determined by your physiology, current eating habits, and the amount of carbohydrates and overall calorie reduction you make. You can experience any of the symptoms from constipation, to frequent headaches, muscle cramps, fatigue, bad breath and even low athletic performance. However, there are alternative low carb foods that can help you keep up with your daily nutrient intake. 

4 Side Effects After Discontinuing a Low Carb Diet 

You may encounter adverse effects as your body adjusts to the end of your low-carb diet. The following are the most common:

1. Gaining Weight

Because most low-carb diets are so restrictive, health experts say it’s not an appropriate plan to follow long-term. Instead, it’s best done for 30 to 90 days. But the problem is that most people will regain much of their lost weight as soon as they return to carbs.

You may notice a rise in weight, usually due to water weight because carbohydrates increase the quantity of water in your body. So, as the amount of water in your body increases, so does your weight. So it isn’t fat gain or unhealthily gained weight.

Weight regain is an issue with any fad diet, but it seems more common with low-carb diets. These back-and-forth weight fluctuations can contribute to an unhealthy relationship with food, leading to disordered eating.

2. Irritability and Fatigue

The rise and fall of blood sugar can leave you exhausted and angry, especially if you add simple carbs and sugars. Most people report that the feeling of irritation is worst for the first three days of discontinuing a low-carb diet but then gets better and dissipates after the first week.  

3. Hunger

You may feel hungry if you are used to the early satiety benefits of a high-fat diet to compensate for the absence of carbohydrates. Furthermore, choosing simple carbohydrates or sugar might cause blood sugar surges, leaving you hungry soon after you’ve stopped eating.

4. Bloating

Increased fibre and carbs may induce bloating during the adjustment phase. High bodily water can also appear as bloat. However, it should settle down, and you should stay hydrated as you acclimatise.

4 Foods to Eat While on a Low Carb Diet 

1. Fruits

Not all fruits contain high levels of carbohydrates. Plus, because of their nutritious value, you can eat most of them in your low carbohydrate diet. They also have natural carbohydrates like glucose and fructose, which aren’t as bad for you as refined sugar.

Berries, watermelon, kiwis, apples, peaches, cherries, and citrus fruits have lower carbohydrate content. They’re high in minerals, including potassium, manganese, and magnesium, as well as antioxidants. Furthermore, they are rich in fibres which help prevent many diseases.

On a low-carb keto diet (<20 grams of net carbs per day), it’s better to choose berries over other fruits. Even a moderately low-carb diet (20-50 grams per day) includes no more than one to two servings of fruits per day. You can eat two or three fruits a day on a liberal low-carb diet (50-100 grams per day).

2. Vegetables

Carbohydrates are lower in vegetables that grow above ground and higher in root vegetables. Vegetables are also high in essential nutrients, vitamins, and antioxidants.

As a result, they are beneficial in treating various diseases, including hypertension. Tomatoes, capsicum, green leafy vegetables, cauliflowers, and other veggies are some of the best to eat.

3. Poultry, Meat and Seafood

Poultry and lean meats are high in protein and low in carbs. Fatty fish are high in omega-3 fatty acids and low in carbs.

They are the good fats that help your body fight harmful cholesterol. You can eat tuna, shrimp, salmon, mackerel, and other fatty fish in your low-carb diet.

4. Nuts

Nuts are a good source of magnesium, potassium, dietary fibre, and antioxidants. Furthermore, nuts that do not have added salt are low in sodium and high in healthful fats.

Omega-3 and 6 fatty acids are abundant in them. Low-carb nuts include almonds, cashews, peanuts, and walnuts.


Cutting down on carbohydrate consumption does not mean reducing the number of healthy nutrients your body requires to function normally. On the contrary, incorporating the right foods and planning a well-balanced diet during a low-carb diet can also lead to several health benefits. You can choose from various food categories, fruits, vegetables, nuts, poultry, meat and even seeds. 


Those with diabetes and those on hypertension or blood sugar-lowering drugs should seek medical advice before starting a low-carb diet. In addition, when attempting a low-carb diet, medicines may need to be modified and should be monitored.

People commonly start a low-carb diet for short-term weight management and blood sugar control. More research is needed, however, to determine the long-term consequences of adopting this diet.

Long-term research on the long-term effects of low-carbohydrate diets says that they may be dangerous, potentially raising your risk of early death, cardiovascular disease, strokes, and cancer.

Pregnant and breastfeeding moms should probably avoid low-carbohydrate diets. Suppose you’re thinking of cutting back on carbs when trying to conceive or expecting or lactating. In that case, it is generally not advised to follow a low-carb diet as energy requirements for those physiological requirements are higher.

The HealthifyMe Suggestion

Eating a low-carb diet means cutting down on the amount of carbohydrates to less than 130g a day. But low-carb eating does not mean no-carb eating. Some carbohydrate foods contain essential vitamins, minerals and fibre, which form an important part of a healthy diet. It’s best to stay on it for no longer than three to six months. Continue having your physician check your blood work closely to make sure to monitor your blood glucose levels, liver and kidney functions.

Low carb diet may suit everyone. No matter what diet or lifestyle you intend to follow, remember that food quality and quantity are important. Eat more vegetables, fewer processed carbs, and don’t be afraid of healthy fats. The best thing you can do is to focus on healthy eating habits for a lifetime.


Like two sides of a coin, a low-carb diet also has its benefits and side effects. The ability to follow a diet also depends on race and ethnicity.

For example, people living in the Asian subcontinent countries find it a little more challenging to follow a low-carb diet than someone living in the west, whose staple diet is dependent on proteins. 

Some people swear by the low-carb diet for weight loss. However, there is a possibility of weight regain. A moderate reduction in carbs probably will not cause any noticeable side effects.

A more considerable decrease in carb intake could cause more pronounced effects, such as headache, fatigue, and changes in bowel habits. It is best to consult a qualified nutritionist to know the best diet for you according to your needs. 

Disclaimer: The purpose of this article is just to disperse knowledge and raise awareness. It does not intend to replace medical advice from professionals.

Frequently Asked Questions (FAQs)

Q. Can a low-carb diet hurt you?

A. No, it cannot hurt you. However, you might face some side effects while following a low-carb diet like tiredness, constipation, initial gain in water weight, and irritability. Collectively, these symptoms are referred to as the “keto flu.” Although low-carb diets have no severe harm, you can take a few steps to lessen their side effects potentially. One such measure is staying hydrated while reducing the carbs gradually. 

Q. How long does it take your body to adjust to a low-carb diet?

A. Your body will take 3-4 days to adjust to a low-carb diet. You may face a fever, tiredness or flu-like symptoms during the 3-4 days, but after that, your body will adapt to it, and you will be able to follow the diet. A positive approach is of utmost importance and will help you gain the benefits of the diet. 

Q. Can you survive without carbohydrates?

A. Some organs can adapt to a life without carbohydrates, but others cannot. Therefore, following a lower-carbohydrate diet essentially means you should decrease, but do not eliminate, the intake of foods containing carbs.

Q. Can a low-carb diet cause anxiety?

A. A low carbohydrate diet can cause tiredness and fatigue but cannot cause anxiety. Anxiety results from emotions and is mostly never connected to low-carb foods. Anxiety typically arises from stress and personal and work problems. 

Q. Can no carbs make you dizzy?

A. Initially, when starting to follow a low-carb diet, you might feel dizzy. Dehydration is the leading cause of dizziness while cutting down carbs. However, after 3-4 days of following a diet, dizziness will gradually go away as the body starts adapting to the diet. 

Q. What does carb withdrawal feel like?

A. A sudden decrease in carbs can cause fluid loss. The fluid loss also causes losses of electrolytes, leading to muscle spasms and muscle weakness. It is also common to feel the effects of dehydration, including fatigue, headache and dizziness. 

Q. How do you feel when you stop eating carbs?

A. Suddenly removing carbs from your diet might make you prone to tiredness, constipation, irritability etc. Some other side effects of discontinuing carbs are increased hunger, bloating, weight gain etc.

Q. Can a low-carb diet make you feel shaky?

A. Yes, you may feel dizzy. Suddenly removing carbs from your diet might make you irritable, dizzy and uneasy. In addition, you might face some side effects while following a low-carb diet, like tiredness and constipation. Although you may lose weight initially, most of it will be water weight. However, once you stop following the low-carb diet and increase your carb intake, you may quickly start gaining weight. That is because reducing carb also reduces glycogen storage in your muscles, and glycogen helps your body retain water. So, a sharp decrease in carbs can cause fluid loss, leading to dehydration. As a result, you’ll feel the effects of fatigue, headache and dizziness.

Q. What do carbs do to your brain?

A. Carbohydrates are food for the brain as the brain utilises only glucose. Proteins break down into glycogen, which the brain can use for fuel but not as well as glucose. As a result, removing carbs from one’s diet may limit the brain’s energy source and alter brain function if other nutrients do not meet energy requirements.

Q. Will I lose weight if I stop eating carbs?

A. You will lose weight if you suddenly stop eating carbs. However, initially, it’s primarily water weight. Another reason low-carb leads to weight loss is that protein and fats are more satiating than carbs. This increase in satiety reduces overall hunger and lowers your overall food intake throughout the day.

Research Sources

  1. Carbohydrate Consumption and Fatigue: A Review
  2. Association of diet and headache
  3. Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial
  4. Low-carbohydrate diets: what are the potential short- and long-term health implications?
  5. Low Carbohydrate Diet
  6. Changes in Quantity and Sources of Dietary Fiber from Adopting Healthy Low-Fat vs. Healthy Low-Carb Weight Loss Diets: Secondary Analysis of DIETFITS Weight Loss Diet Study
  7. Ketogenic Diet for Obesity: Friend or Foe?

About the Author

Parul holds a Masters of Medical Science in Public Health Nutrition from the University of Glasgow, Scotland, and has worked across the globe from the U.K to New Zealand (NZ) gaining her License with the Health Professionals Council (HPC, UK) and the NZ Nutrition Council. From being a Gold medalist in Clinical Nutrition to being awarded an internship with World Health Organisation (WHO, Cairo, Egypt) and Contracts with CDC Parul has had a wide spectrum of work experiences. She is very passionate about Nutrition and Fitness and holds strong to her guiding mantras ‘ Move more’ and ‘Eat Food that your grandmother can recognize’!

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