Why Do I Feel Weak on the Ketogenic Diet?

You can prevent dehydration by making sure you're drinking plenty of water, in addition to getting enough electrolytes.
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The low-carb, high-fat ketogenic diet promises weight loss, improvements in blood sugar and boosts in energy. So why are you feeling weak on keto instead of jumping out of bed at the crack of dawn ready to tackle your to-do list?


According to a report published in PeerJ in March 2018, adverse symptoms of keto occur because when your insulin levels drop, you also lose water, potassium and sodium. This can leave you dehydrated and feeling weak.

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If you're wondering why you feel weak on the ketogenic diet, the likely answer is dehydration. As your body adjusts to burning fat for energy, it can prompt water loss that always causes a loss of electrolytes and leaves you feeling drained and weak.

Using Glucose for Energy

Glucose, a type of carbohydrate, is the main source of energy for your body. When it needs energy, your body will turn to carbohydrates before it goes for other sources, like fat.

When you eat carbohydrates, your body breaks them down into their most basic form: the simple sugar, glucose. Glucose travels to your blood where its presence triggers the beta cells in your pancreas to release the hormone insulin. Insulin rushes into the blood and attaches to the glucose.

Glucose and Glycogen

Some of that glucose is carried to your cells where it's immediately used by your body for energy. Once your body's immediate energy needs are met, some of the remaining glucose is converted into another compound called glycogen. Insulin carries glycogen to your liver and your muscles, where it's stored until your body needs more energy.


However, according to a report published in Nutrition Reviews in February 2018, your liver can only store about 80 grams of glycogen at a time. Once these glycogen stores are full, your body has to find another place for leftover glucose. It takes anything that remains and converts it into triglycerides, a form of fat, then stores it in your adipose, or fat, tissue. If you keep eating carbohydrates, this cycle repeats over and over.

The Science of Ketosis

A March 2019 update from StatPearls describes the ketogenic diet working by interrupting this glucose and glycogen cycle and forcing your body to use fat for energy instead. If you restrict carbohydrates in your diet, your body uses up the glucose it has available, then turns to the glycogen stored in the liver.


Once the glycogen is used up, and not replenished by more carbohydrates, your body looks somewhere else for energy. When this happens, it starts breaking down the fatty acids in your fat stores and turning them into energy-rich substances called ketones.


In the absence of glucose, these ketones serve as your body's immediate energy source. If you keep your body from gaining access to glucose by eating a low-carb diet, your body will continue to break down your own body fat and convert it into energy.


Read more: How Long Does It Take for the Ketosis Diet to Work?

What Is the Keto Flu?

If you're feeling weak on keto, especially in the initial states, it's likely that you're going through a transition period called keto flu. You don't actually have the flu, but the symptoms you may experience mimic those that would accompany it. In addition to weakness, other possible symptoms include:


  • Nausea/vomiting
  • Headache
  • Fatigue
  • Dizziness
  • Insomnia
  • Constipation

Weakness and Dehydration on Keto

It may seem strange for flu-like symptoms to develop just from following a new diet, but there's a physiological reason that this happens. When you stop eating a lot of carbohydrates, your blood glucose levels drop, which also triggers a drop in insulin. According to the authors of the March 2018 report in PeerJ, insulin naturally makes your body retain both water and salt.


When insulin levels drop, your body gets rid of that water and salt (sodium), plus magnesium and other electrolytes like potassium in your urine. If you're feeling weak on keto, it's generally because you've lost too much water and electrolytes, and you haven't properly replaced them, leaving you dehydrated. In addition to weakness, you may also experience constipation, headaches, muscle cramps and rashes.

Drinking Enough Water

Drinking enough water is important no matter what kind of lifestyle you're living, but it's especially vital when following a keto diet because you have to replace all of the water that's lost. As a general rule, aim to drink about half your body weight (in pounds) in ounces of water.



That means if you weigh 200 pounds, you'll need about 100 ounces of water every day. If you weigh 150 pounds, that number drops to 75 ounces daily.

Replenishing Your Electrolytes

Since you're losing electrolytes in addition to water, it's also helpful to replenish those electrolytes to resolve any general weakness or muscle weakness on keto. Sea salt is best, as it contains trace amounts of the minerals potassium, magnesium and calcium in addition to sodium.

Adding sea salt to your food while you're cooking can help replenish lost electrolytes and maintain electrolyte balance. You can also opt for electrolyte-enhanced water or make your own electrolyte replacement sports drink by adding a pinch of sea salt to some water with a little bit of fresh lemon. Talk to your doctor about how much salt and other electrolytes you should be taking in.

Avoid commercial sports drinks, even those advertised as low-carb or keto-friendly. These types of drinks typically contain artificial sweeteners that come with their own set of negative effects.

Read more: The Benefits of Electrolytes in Water

Consider Other Possibilities

If you've checked your water and electrolyte intake and it's normal and you're still feeling weak on keto, it's possible that you're just not eating enough. When starting a new diet, many people think they have to restrict their food intake significantly, especially if weight loss is the goal, but overdoing it can have negative side effects, like fatigue and weakness.

Track your calories and your macronutrient intake, if you're not already, and make sure you're meeting your needs. If you're eating too little, incorporate more healthy fats, like avocado, olive oil and salmon, and high-quality protein, like chicken and grass-fed beef.




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