Low Carb Diet Fatigue: Understanding and Overcoming Energy Slumps

When embarking on a low-carb or ketogenic diet, it’s not uncommon to experience a drop in energy levels. This phenomenon, often referred to as “low carb diet fatigue,” is a common side effect, especially for those new to this dietary approach. However, with the right strategies and understanding, you can overcome this initial slump and enjoy the full benefits of a low-carb lifestyle.

The Science Behind Low Carb Diet Fatigue

A low-carb diet, as the name suggests, involves a significant reduction in the intake of carbohydrates 1, which are the body’s primary source of energy under normal dietary conditions. This reduction is coupled with an increase in fat consumption. The rationale behind this dietary shift is to prompt your body to switch its primary energy source from glucose, derived from carbohydrates, to ketones, derived from fats. This metabolic shift is known as ketosis 2.

Understanding Ketosis

Ketosis is a metabolic state where the body uses fat as its primary source of energy instead of carbohydrates 3. When carbohydrate intake is low, the body’s glucose reserves gradually deplete. As a result, the liver starts converting fatty acids into molecules known as ketone bodies, or ketones, which can be used as an alternative energy source.

In the long run, being in a state of ketosis can lead to several benefits, including weight loss, increased energy levels, and improved cognitive function 2. This is because fats are a more efficient fuel source than carbohydrates, and ketones are a more efficient energy source for the brain than glucose.

The Transition Period: From Glucose Burning to Fat Burning

However, the transition from a glucose-burning state to a fat-burning state can be challenging for the body 1. During the initial stages of a low-carb diet, your body is still accustomed to using glucose for energy. As you reduce your carb intake, your body may struggle to adapt to using fat and ketones as its primary fuel source.

This struggle is due to the fact that your cells, particularly your brain cells, are used to using glucose for energy 2. When glucose becomes scarce, these cells can’t get enough energy, leading to feelings of fatigue or tiredness. This period of adjustment is often referred to as the “keto flu” because its symptoms, which include fatigue, brain fog, and irritability, can resemble those of the regular flu.

The duration of the keto flu varies from person to person. It can last from several days to a couple of weeks, depending on factors such as individual metabolic flexibility, the extent of the dietary change, and how strictly the low-carb diet is followed.

Learn more: What Happens in the First Two Weeks of a Low-Carb Diet?

The Role of Insulin and Glucagon

Another important aspect of the science behind low carb diet fatigue involves the hormones insulin and glucagon 4. Under normal dietary conditions, a high intake of carbohydrates leads to increased levels of glucose in the bloodstream. This triggers the release of insulin, a hormone that helps cells absorb glucose and store it for later use.

On the other hand, when carbohydrate intake is low, insulin levels drop, and the body starts producing more glucagon, a hormone that signals the liver to produce glucose from stored glycogen and promotes the breakdown of fats into ketones. This shift in hormonal balance is crucial for the body’s transition into ketosis but can also contribute to the initial feelings of fatigue as the body adjusts to its new metabolic state.

In conclusion, the science behind low carb diet fatigue involves a complex interplay of metabolic and hormonal changes as the body adapts to using fat and ketones as its primary source of energy. Understanding these processes can help individuals better manage the transition period and minimize the symptoms of the keto flu.

Symptoms of Low Carb Diet Fatigue

Aside from general tiredness, other symptoms associated with low carb diet fatigue can include muscle cramps, changes in bowel habits, headaches, skin rashes, and bad breath 6. These symptoms are typically temporary and tend to dissipate as your body adjusts to the new diet 7.

Strategies to Combat Low Carb Diet Fatigue

1. Ensure Adequate Fat Intake

When you reduce your carbohydrate intake, your body needs to replace those calories with another energy source, and that’s where dietary fats come in 8. Fats are not just a replacement for carbs; they’re a necessary nutrient that supports various bodily functions, including vitamin absorption, hormone production, and brain function.

In a low-carb diet, aim to get about 60%-80% of your total daily calories from healthy fats. These include monounsaturated fats found in foods like avocados, olives, and almonds, and polyunsaturated fats, including omega-3 and omega-6 fatty acids, found in fatty fish, walnuts, and flaxseeds. Saturated fats, found in coconut oil, butter, and red meat, can also be included but in moderation.

2. Eat Regularly

While a low-carb diet can be satiating due to the high protein and fat content, it’s essential not to let your calorie intake drop too low 9. Consuming too few calories can slow down your metabolism, leading to fatigue and hindering weight loss.

Ensure you’re eating three balanced meals a day, each containing a decent amount of fat and protein. Including a source of protein in every meal can help control hunger and maintain muscle mass, while fats can keep you feeling satisfied for longer.

3. Consume Nutrient-Dense Foods

In a low-carb diet, every gram of carbohydrate must count. Opt for nutrient-dense foods that provide essential vitamins, minerals, and fiber.

Green leafy vegetables, bell peppers, broccoli, and other non-starchy vegetables are excellent choices.

Include high-quality protein sources like grass-fed red meat, poultry, and oily fish, which provide essential amino acids and omega-3 fatty acids. These foods not only help meet your macronutrient needs but also supply essential micronutrients that support overall health and energy levels.

4. Gradually Reduce Carb Intake

A sudden and drastic reduction in carb intake can lead to strong withdrawal-like symptoms, including severe fatigue. To minimize these effects, consider gradually reducing your carb intake.

Start by eliminating obvious sources of excess carbs, such as sugary drinks, candies, and desserts. Then, move on to refined grains and baked goods. As you get comfortable with these changes, you can start reducing your intake of complex carbs like whole grains and starchy vegetables until you reach your desired carb target.

5. Stay Hydrated and Maintain Electrolyte Balance

Hydration and electrolyte balance play a crucial role in energy levels and overall health. When transitioning to a low-carb diet, your body tends to excrete more water and electrolytes, which can lead to dehydration and imbalances.

Ensure you’re drinking enough water throughout the day and consuming foods rich in electrolytes such as potassium, magnesium, and sodium. These minerals are essential for various bodily functions, including nerve and muscle function, maintaining fluid balance, and regulating blood pressure.

6. Exercise Regularly

Regular exercise is beneficial for overall health and can aid the transition to a low-carb diet. While you might feel less inclined to exercise during the initial stages of a low-carb diet, maintaining a regular, gentle exercise routine can help your body adjust to its new fuel source.

Exercise promotes fat burning and helps regulate blood sugar and insulin levels. Start with low-intensity activities like walking or yoga and gradually increase intensity as your energy levels improve.

7. Consider Supplements

Certain supplements can help ease the transition to a low-carb diet and alleviate symptoms of low carb diet fatigue. Exogenous ketones and MCT oil can provide an instant energy boost by raising your blood ketone levels, providing an alternative energy source for your brain and muscles.

A high-quality multivitamin can help bridge any potential nutritional gaps, ensuring you’re getting all the essential vitamins and minerals your body needs. Always consult with a healthcare professional before starting any new supplement regimen.


Low carb diet fatigue is a common but manageable side effect of transitioning to a low-carb or ketogenic diet. By understanding the cause and implementing the strategies outlined above, you can successfully navigate this initial energy slump and reap the benefits of your new dietary lifestyle. Remember, everyone’s body responds differently, so it’s essential to listen to your body and adjust your approach as needed.


  1. Mayo Clinic
  2. Healthline
  3. WebMD
  4. Medical News Today
  5. Diabetes UK
  6. Livestrong.com
  7. Gainful
  8. Carbophobic
  9. Fatigue to Flourish

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