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Low-Carb, Keto Fatigue: Why Am I Feeling Tired on Keto?


The ketogenic diet is an effective diet for weight loss. Scientific evidence shows that keto also supports neurological, cardiovascular, metabolic, and cellular health[*].

If you’re feeling tired all the time on keto, you’re probably wondering if you’re doing something wrong, or you might think that keto isn’t a good fit for your body.

Here’s a look at the common causes of exhaustion or low energy on keto, and what you can do to troubleshoot that fatigue so you feel your best while still getting all the benefits of a ketogenic diet

Causes of Fatigue on Keto

There are several reasons you may feel fatigue on the keto diet. Fortunately, most of them are easy to fix.

Keto Flu

One common cause of fatigue is the keto flu

When you first start keto, your metabolism has to switch from burning carbs for fuel to burning fat for fuel. This is a major metabolic change and it takes your body a few days to start efficiently using fat as its main energy source. 

During this adjustment period (called keto adaptation), you may experience fatigue, headaches, and other minor side effects. It only takes a few days for your metabolism to switch into fat-burning mode, so keto flu usually only lasts for the first week of keto. 


When you eat carbs, your body converts them into sugar and sends them into your bloodstream. In response, your pancreas releases insulin to keep your blood sugar from getting too high. 

When you’re on a keto or low carb diet, your insulin levels stay very low and stable. You aren’t eating carbs or sugar, so insulin doesn’t have to do its job. 

However, insulin does more than just stabilize blood sugar. It also tells your kidneys to hold onto sodium, potassium, magnesium, and other electrolytes. 

In other words, on a low carb diet, your body excretes a lot more water and electrolytes[*]. That means you can salt your food without worrying about your blood pressure — but it also means if you don’t replenish those electrolytes, you can get dehydrated. 

Dehydration leads to fatigue, brain fog, muscle cramps, and other issues[*]. For that reason, a lot of keto dieters take an electrolyte supplement and drink extra water. 

Not Enough Calories

Ketosis suppresses appetite, making it easier to stay in a calorie deficit throughout the day[*]. It also speeds up your metabolism — you burn about 300 extra calories a day while on a keto diet[*]. 

Basically, on keto, you burn more body fat while feeling less hungry. These metabolic changes make keto excellent for weight loss

However, it’s also easy to undereat on keto because your appetite is suppressed. While a mild calorie deficit is good for sustainable weight loss, you may be going too low in calories unintentionally. 

Undereating reduces your body’s production of thyroid hormone and other energy hormones, and over time can even crash your metabolism[*].

Not eating enough can leave you feeling exhausted and is a relatively common problem with people who are new to keto dieting. 

Intense Exercise

Studies are mixed when it comes to keto and exercise[*]. 

While many people seem to do fine working out on keto, others run out of energy and see a decline in exercise performance and energy levels when they don’t eat carbs. 

If you’re following a rigorous workout plan while on keto and you find you’re running low on energy, you may want to introduce carbs back into your diet in a targeted way. 

Low Quality Food

Not all keto food is created equal. There are processed keto snacks that technically fit keto macros but still aren’t good for you. 

If you’re eating pork rinds and sugar-free frosting all day, you’ll probably run out of energy while on keto, even though your body is in ketosis. 

Instead of eating dirty keto, your best bet is to prioritize fresh vegetables, high-quality protein like steak or fish, and plenty of healthy fats. 

How to Prevent Fatigue on Keto

With a few changes to your diet or lifestyle, there’s a good chance that you can restore your energy levels and feel great while on a keto diet. 

Here are eight ways to prevent fatigue while eating keto. 

1. Eat More Calories

If you’ve tried low-calorie diets in the past, you might be bringing the wrong mindset to keto.

Evidence shows people often burn fat and lose weight on keto without counting or intentionally restricting calories[*][*].

Even if your goals include weight loss, you can experiment with eating more calories to boost your energy levels and fight fatigue.

For the next 2-4 weeks, eat healthy keto-friendly whole foods and allow your appetite to guide your food intake. 

You may be surprised to discover that your tiredness vanishes–without slowing down your fat loss results.

And if you’re worried that you have a slow metabolism, don’t be. It’s usually not a big deal on keto.

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2. Eat More Fat

On the keto diet, the vast majority of the energy your body uses comes from fat calories (in the form of stored body fat as well as dietary fats you eat).

But similar to the unhealthy low-calorie mindset, beginners sometimes bring a “fat-phobic” perspective to keto.

Guess what happens when you’re afraid of eating healthy fats on the ketogenic diet, where fat is your primary source of energy? Naturally, with insufficient fuel in the form of fats, you’re going to feel fatigued on keto.

The good news is that fat doesn’t make you fat. So make sure healthy fats feature prominently at every keto meal you eat.

3. Eat Regularly

Beyond your calorie and fat intake, your meal schedule can also affect your energy levels.

Particularly for people just starting keto, who aren’t fully fat-adapted yet, eating regularly is one of the best ways to provide plenty of energy for your brain and body.

And although plenty of evidence supports intermittent fasting, it doesn’t work for everyone.

Try eating at least 3 meals a day at first, spread evenly throughout the day. If that doesn’t solve your fatigue, you can also add a few low-carbohydrate, high-fat snacks

Mastering meal prep can help you eat healthy keto meals with less disruption to your daily schedule.

And if you implement keto fasting, make sure to do it in a structured, intentional way. Don’t skip meals randomly when you’re stressed or short on time, because doing so may worsen your fatigue.

4. Ditch “Dirty Keto”

Dirty keto is an approach that follows keto macros, but allows lots of unhealthy foods.

As you might imagine, eating fast food and other processed foods that fit keto macros exposes your body to artificial flavors, colors, and other unnatural additives.

Over time, it may also result in omega-3 to omega-6 imbalances, vitamin and mineral deficiencies, and other issues that could worsen your fatigue.

If you’ve been following dirty keto, clean up your diet and watch your fatigue diminish.


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5. Check Your Carb Intake

The ketogenic diet is a very-low-carb diet.

But that doesn’t necessarily mean you have to eat zero carbs (unless you’re using keto to treat epilepsy).

For most people, the correct amount is somewhere between 30-50 grams of net carbs per day.

Even if you think you’ve dialed in your carb intake, though, being tired all the time is an occasion to take a closer look.

First, you’ll want to test your ketone levels daily to ensure you’re actually in ketosis. If you’re not, lowering carb intake may address fatigue.

Testing your blood sugar regularly is a related strategy that may provide additional insight.

Second, some people actually benefit from eating more carbs. 

If you’re following the standard keto diet, keto-friendly fruits and veggies are the optimal carb sources to ensure you remain in ketosis.

Athletes and very active people can also use targeted keto or cyclical keto to reverse fatigue and provide energy for physical activity.

6. Check Your Macros

If nothing else is working so far, examine the big picture of your keto macronutrient intake.

Most people should follow these macros on the standard ketogenic diet:

  • 65-80% of calories from fats
  • 20-35% of calories from protein
  • 5-10% of calories from net carbs 

Consuming insufficient protein is a common keto mistake, especially for active individuals.

If you’re not a math person, use the keto macro calculator to learn the best macros for your goals. 

Then you can use My Fitness Pal or another free macro app for a few weeks to ensure you stay on track.

7. Move Your Body

Keto is probably the closest thing to a miracle diet, but you still need regular exercise for optimal weight loss and general health purposes.

And if you’re feeling tired on keto, a sedentary lifestyle could be the culprit.

As counterintuitive as it sounds, studies are clear that sitting around can make you feel more tired, not less[*][*].

You can become more active by following an easy keto exercise plan for beginners, or by doing whatever activity you enjoy. Even brisk daily walks are far better than nothing.

However, if exercise makes your fatigue worse, you might be dealing with an underlying health concern. In that case, you should schedule a doctor visit to get to the bottom of your tiredness.

8. Find the Right Keto Supplements

Keto supplements can help to maintain a state of ketosis, as well as support a healthy keto lifestyle.

Here are the top supplements to consider for fatigue on the keto diet:

If you’re feeling tired on keto, high-quality supplements work exceptionally well in combination with the other strategies we’ve covered.

The Takeaway

The keto diet is unlikely to cause lasting fatigue, but low levels of energy can be a sign you need to make changes or address an underlying problem.

If your sluggishness doesn’t go away on its own within 1-2 weeks, you may be able to reverse it by adjusting calories, macros, food selection, activity, or supplements.

Remember that other things can cause low energy on keto, too. You may need more sleep, better stress management, or to speak to a physician about possible medical issues.


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