Does a Low-Carb Diet Make You Tired?

A low carb diet might have some side effects.
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Low-carbohydrate diet plans have become incredibly popular. These diets can support weight loss and benefit your health in various ways. Unfortunately, the average low-carbohydrate diet may be accompanied by side effects, like the "keto flu" and bouts of low-carb diet fatigue.



According to a September 2018 study published in the Indian Journal of Medical Research and a December 2018 study from the Journal of the College of Family Physicians of Canada, loss of energy is a common side effect associated with the low-carbohydrate diet.

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Following a Low-Carbohydrate Diet

Most Americans follow a Western diet and obtain most of their daily calories from carbohydrates. According to the Mayo Clinic, the daily recommended intake of carbohydrates ranges between 45 and 65 percent.

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People following a Western diet tend to consume nutrients that fall within the Food and Drug Administration (FDA) recommended daily values. They usually ingest about 65 grams of fat, 50 grams of protein and 300 grams of carbohydrates per day.

Low-carbohydrate diet plans are exactly the opposite of a typical Western diet. Dieters are meant to obtain most of their calories from fat, rather than carbohydrates. However, the number of carbs you consume on a low-carbohydrate diet can vary.

Certain low-carb diets, like the ketogenic diet, heavily restrict carbohydrate consumption to just 5 to 10 percent of your daily calories. According to the September 2018 study published in the ​Indian Journal of Medical Research​ and the December 2018 study from the ​Journal of the College of Family Physicians of Canada​, carbohydrate intake in ketogenic diets is typically between 20 and 50 grams per day.


Other low-carbohydrate diet plans are much more liberal. The Atkins diet, for instance, starts out as a strict low-carb diet but gradually becomes less restrictive. The most liberal Atkins diet allows for as much as 100 grams of carbohydrates per day. This is around 20 percent of the calories from a 2,000-calorie diet.

You may even see studies, like a September 2018 study in ​The Lancet​, refer to diets with a carbohydrate consumption of 40 percent per day or less as low-carb diets. However, such liberal low-carbohydrate diet plans are less typical. According to the Mayo Clinic, low-carb dieters typically consume 20 to 60 grams of carbohydrates per day.


Read more:10 Reasons to Not Cut Carbs Completely Out of Your Diet

Low-Carbohydrate Diet Pros and Cons

Low carbohydrate diets have a variety of benefits. They're best known for helping people lose weight. However, according to the study published in the ​Indian Journal of Medical Research,​ low-carbohydrate diet plans can also help treat epilepsy and manage Type 2 diabetes.



The Harvard T.H. Chan School of Public Health also reports that low-carbohydrate diet plans may help improve aspects of cardiometabolic health. These diets can help reduce triglyceride levels, cholesterol and blood pressure. People obtain the most health benefits when they follow low carbohydrate diet plans that incorporate lots of plant-based fats and proteins, like avocados and legumes.

Of course, the low-carbohydrate diet is not without its downsides. The ​Journal of the College of Family Physicians of Canada​ and the ​Indian Journal of Medical Research​ studies report that the low-carbohydrate diet can cause unpleasant side effects, which include:


  • Muscle cramps
  • Bad breath
  • Changes in bowel habits, including constipation and diarrhea
  • Headache
  • Skin rashes
  • Loss of energy
  • "Keto flu"

Fortunately, most of these negative side effects are temporary. They typically go away after the first few weeks of following a low-carbohydrate diet.

Read more:9 Surprising Reasons You're Tired All the Time


The Low-Carb Diet and Fatigue

It's not unusual to experience unpleasant side effects at the start of a low-carb diet. Fatigue can occur on its own, or in conjunction with the so-called "keto flu." An April 2019 review in the journal Nutrientsdefines the keto flu as a temporary condition that produces symptoms like lightheadedness, dizziness, constipation and tiredness. A November 2019 study in the journal Nutrition: X also mentions symptoms like muscle weakness, muscle cramps, headaches, changes in mood and bloating.


According to the Mayo Clinic and the study in ​Nutrition: X​, low-carb diet fatigue and other symptoms are likely to occur when you dramatically reduce your carbohydrate intake. The study in ​Nutrition: X​ even referred to this brief period at the start of a low-carbohydrate diet as "carbohydrate withdrawal."


If your staple foods include things like sandwiches, pasta, pizza, rice or other grain-based products and you suddenly start a low-carbohydrate diet, you're particularly likely to experience carbohydrate withdrawal. However, fatigue and keto flu can occur even if you haven't been regularly eating carbohydrate-rich foods.

Read more:Negative Side Effects of a Low-Carb Diet

Managing Low-Carb Diet Fatigue

If you're experiencing mild negative side effects associated with the low-carb diet, like fatigue or headaches, you'll be pleased to know that these side effects tend to pass quickly. According to a March 2018 study in ​PeerJ Life & Environment​, mild side effects are usually due to water loss, electrolyte imbalances and fluctuations in blood glucose. These issues typically start to go away around the fourth day you're on the low-carbohydrate diet.

Keto flu, which tends to appear slightly later on, tends to be accompanied by more serious symptoms. According to Harvard Health Publishing, keto flu might appear two to seven days after you start a low-carbohydrate diet. While most people do experience the mild, short-term side effects associated with low-carbohydrate diets, the more severe keto flu does not occur in everyone.

However, according to the study published in ​Nutrition: X​, symptoms associated with carbohydrate withdrawal can occur on liberal low-carbohydrates diets, in which 25 percent of the calories come from carbohydrates, and strict, ketogenic low-carb diets, which have 5 percent of their calories from carbohydrates.

Essentially, this means that people may experience symptoms of fatigue regardless of whether they've chosen a liberal or a strict low-carbohydrate diet. However, the symptoms of keto flu get worse the greater the reduction in carbohydrate consumption.


Strategies for Managing Keto Flu

Harvard Health Publishing recommends sticking with your low-carbohydrate diet, because keto flu is unpleasant but temporary. Fatigue with keto flu can be a major issue, but after it passes further low-carb diet fatigue is unlikely. However, if you really can't cope with keto flu symptoms, you can always try gradually easing yourself into a low-carbohydrate diet.

Instead of dramatically cutting carbs all at once, try eliminating extremely unhealthy carbohydrate-rich foods, like candy and sugary desserts. Continue by removing refined grains and baked goods, like cakes and pastries, from your diet. Then eliminate unrefined grains; starchy vegetables, like potatoes; and high-carb fruits.

By this point, you'll find that most of the foods you're eating can still be included in a low-carbohydrate diet. You simply may need to modify the ratio of macronutrients you're consuming based on your specific low-carbohydrate diet needs.

The study in ​Nutrition: X​ also suggests making sure you're consuming enough calories. People often don't consume enough calories when they start a low-carbohydrate diet. It can be hard to balance your macronutrient intake appropriately. New followers of the low-carbohydrate diet may not consume enough fat, which results in this insufficient calorie consumption.

Dietary Changes for Keto Flu

If you've had keto flu for a while or your symptoms are particularly debilitating, consider the foods you've been eating. Many dieters avoid fatty foods, and this habit can be hard to break when starting a strict low-carbohydrate diet for the first time.

According to the Harvard T.H. Chan School of Public Health, the healthiest low-carbohydrate diets are those that incorporate healthy plant-based fats. Healthy fats include oils like extra virgin olive oil, avocado oil, sesame oil and nut-based oils.


You can also incorporate moderate amounts of coconut oil into your diet or supplement your diet with ketogenic medium chain triglyceride (MCT) oil. Many people enjoy making smoothies with keto-friendly fruits like berries and melons. Mixing MCT oil into your smoothies is an easy way to increase your fat and calorie consumption.

Healthy low-carbohydrate foods can include milk-based products, as long as they're consumed in moderation. You can also swap products like butter out for alternatives like ghee.

Instead of only eating milk-based cheeses, creams and yogurts, try integrating soy or nut-based alternatives into your diet. You can easily swap your milk-based yogurt, sour cream or cheese for products like almond yogurt, cashew sour cream and soy cheese.

Beware of the hidden added sugar content in these products, though. Yogurts, especially flavored ones, are often sweetened with ingredients that are not low-carb diet friendly.

Other sources of healthy fats include fatty fish like omega-3 rich salmon, herring and mackerel. Fruits like avocados, nuts and seeds also tend to be rich in these healthy polyunsaturated fatty acids.

MCT Oil for Keto Flu

Many low-carb dieters consume MCT oil because it supports ketosis. However, a May 2018 study in the ​Journal of Nutrition and Metabolism​ tried supplementing low-carbohydrate diets with MCT oil to prevent and counteract the effects of keto flu.

This small, 28-person study found that there was a reduction in low-carb diet fatigue, keto flu and related symptoms when dieters consumed 90 milliliters of MCT oil each day for the first 20 days of their diet. However, MCT supplementation didn't resolve all of the study participants' symptoms, like mood fluctuations. It also may have caused dieters to experience increased abdominal pain.

MCT oil is safe to consume, so there's nothing wrong with integrating it into your diet. According to Harvard Health Publishing, this oil can help prevent fat storage and promote feelings of fullness, helping you adjust to your new low-carbohydrate diet. However, a larger-scale study needs to be performed before the benefits of MCT oil in relation to reducing keto flu symptoms can be stated for certain.