Why Am I So Exhausted On The Keto Diet?

The ketogenic diet is an incredibly popular protocol, with proven benefits for weight loss, hypertrophy, and improved health and wellbeing. Utilising a low carb approach (50g or fewer as a typical daily intake) with high fat content (70-80% of total caloric intake), it is perfectly safe for dieters to use, but may come with some unpleasant side effects, especially at the beginning.

One of the biggest side effects is the ‘keto flu’. Keto flu is less a side effect in its own right, but rather more of a grouping of common side effects that lead a dieter to feeling as though they are run down. It is most often associated with a feeling of lethargy and a lack of mental clarity and can make dieters feel exhausted out of proportion to their activity levels.

But what exactly is keto flu, will it get to you, and can it be overcome?

Keto Flu

The keto flu is a grouping of symptoms commonly experienced by people undertaking a ketogenic diet and is most often felt in the initial few weeks, as the body gets used to its new macronutrient intake and the process of ketosis begins.

Though fans of the ketogenic diet often cite improved energy levels as one of its main benefits, this boost doesn’t always happen, at least at first. The keto flu is exactly what it sounds like: flu-like symptoms that can lay you low and rob you of all energy and mental clarity for a period of days, weeks or even months.

The symptoms are caused by the body’s adaptation as it becomes used to subsisting on fat fewer grams of carbohydrates per day than it is accustomed to: the lack of glycogen that results from this lack of carbohydrates immediately elicits fatigue and feelings of exhaustion.

This lack of glycogen is the point of a ketogenic diet. It forces the body to create ketones from fat to use in their place. Fat is more usually reserved as a fuel of last resort, to be used when glucose is unavailable: the keto diet forces this process to become primary. These ketones become the body’s main source of energy and are largely responsible for the heightened perception of energy that many people find on the keto diet.

The process of creating ketones as energy from fat is ketosis, and can be elicited by:

  • Starvation
  • Fasting
  • Adopting a low-carb diet

The drastic cutting down of carbohydrates is something of a shock to most people. The average diet can contain anything from 2-300g of carbs per day, whilst the ketogenic diet requires fewer than 50g. There is a lag between adopting such a major change to the diet and the body’s adaptation: keto flu usually hits in this window, between cutting down carbs and the point at which your body can sufficiently power itself on ketones.

Some people may transition to a ketogenic diet without any side effects, hitting ketosis early and experiencing plenty of energy. However, many may experience one or more of the following symptoms:

  • Nausea 
  • Vomiting
  • Constipation
  • Diarrhoea
  • Headache 
  • Irritability
  • Weakness
  • Muscle cramps
  • Dizziness
  • Poor concentration
  • Stomach pain
  • Muscle soreness
  • Difficulty sleeping
  • Sugar cravings

These symptoms are common in the early stages of the ketogenic diet, beginning in the first few days and lasting between 1-3 weeks. However, they may also appear or reappear later on and may last much longer. Altogether, they represent a great depletion of energy and heightened feelings of fatigue: this is the reason that so many people feel exhausted on the keto diet.

How Can You Deal With Keto Flu?

As and when it hits you, keto flu can really lay you low and may make you consider dropping the ketogenic diet altogether. However, this needn’t be the case: the flu doesn’t have to last for weeks, and it doesn’t have to be anything like as debilitating as many people find it. You simply need to know how to properly deal with it.

Apart from supplements, there are a few things we can put in place to make short work of the keto flu and give you your energy back.



We’ve gone over the importance of water intake on a keto diet before.

When you cut down on dietary carb intake, your body’s water stores will diminish. As carbs become scarcer in your everyday diet, your body will turn to the carbs it already has in storage and will burn them for fuel. Glycogen is stored alongside water, and this stored water is released at the same time as glycogen is used. As your body can hold up to a pound of glycogen at any one time, this can mean several pounds of water loss as it is shifted.

When you limit your carbs as much as you will do on a ketogenic diet, drinking water becomes crucial. As your body will no longer be storing water as it would in the presence of large amounts of glycogen, it will begin to run a water deficit: critical dehydration soon follows on from this.

Amongst the other symptoms of dehydration, the human body often experiences increased fatigue, instances of muscle cramping, diarrhoea, low blood pressure and a lack of mental clarity, all of which enforce and exacerbate the negative effects of keto flu.

Replacing this fluid is vital, as is keeping a continuous flow of water into the body. Make sure to drink often and be watchful for symptoms of dehydration.

Replace Your Electrolytes

Electrolytes and a lack thereof can be a crucial component of diminished energy on a keto diet.

Insulin levels decrease on the ketogenic diet. When insulin is depleted, kidneys release some of the body’s excess sodium. In addition, foods rich in potassium (a vital electrolyte) are often lacking on keto diets, as they are typically starchy vegetables and fruits.

Inadequate electrolyte reserves can be responsible for low energy and feelings of fatigue, and can also lead to headaches and issues with sleeping: replacing dietary electrolytes may therefore help reduce keto-flu symptoms. Getting plenty of foods rich in electrolytes, considering relying on electrolyte supplementation, and heavily salting food can all go a long way to decreasing the tiredness common to the early days of keto diets, and are well worth continuing long-term.

Leafy green vegetables and avocados are great keto-friendly sources of electrolytes.

Keep Fats And Calories High

It’s quite common for people undertaking a ketogenic diet to under eat. This is understandable: many are seeking to lose weight, and it seems intuitive therefore to eat less, and it’s also a lot harder to overeat on fat and protein than it is on carbs.

However, your body may not need this extra stress, especially when you’re already taxing it by having it switch its energy use from glucose to ketones. It may also not need the further energy depletion inherent to a caloric deficit.

It’s a good idea to do one thing at a time. Either hit a caloric deficit or begin a ketogenic diet. Don’t do both at the same time. Try going for a keto diet for a month or so, before bringing your total caloric intake down.

In addition, it may be worth gradually diminishing your carb intake, rather than cutting it down in one go over night. You will be wanting to bring it down from a typical 200g or so to about 50g. Try aiming at reducing your intake in stages, aiming at reducing 50g per week for three weeks. Doing this, whilst simultaneously increasing fat and, to a lesser extent, protein to plug the caloric gap, may help make the transition smoother. It may save your from suffering the worst of those keto-flu symptoms.

Also, don’t try to lose too much weight at once, even if weight loss is your overarching goal. 1-2lbs per week (roughly 0.5-1kg) is about right for most people. If you have a body fat percentage below the mid-twenties, you will want to keep it on the low side.

If you cut too quickly, you will likely hit a catabolic state, in which you’re digesting your own muscles for fuel rather than getting into ketosis. So, switch to fats and proteins, keep your carbs low, but keep your total caloric intake up to where it needs to be.

If You Need To, Train Less Intensely

If You Need To, Train Less Intensely

The ketogenic diet can bring great athletic benefits in the long run, as more fats and protein improve recovery and more energy leads to better performance. However, in the short term, this may not be the case.

Exercise is important, and many keto dieters will be going into it for these athletic advantages, but the best training regime is always the one that is most appropriate. In this case, less may be more. Fatigue, muscle cramps and stomach discomfort are common side effects grouped in with keto flu, so it may be a good idea to give your body a rest. If you experience symptoms of keto flu and you feel your energy levels dropping, cut down the intensity. It will only be for a few weeks, most likely.

Consider switching out your exercise for a milder form. Instead of lifting weights intensely, try moderate walking and gentle yoga for a couple of weeks, until the keto flu passes. If you want to carry on with your current regime, try working less strenuous aspects: lift less weight, and work on form and mobility, for instance. Instead of sprint training, try longer distance, gentler jogging.

Make Sure You’re Sleeping

Anyone who goes without adequate sleep will get exhausted: so much is obvious.

However, combine this with any underlying condition or lifestyle factor- like beginning a ketogenic diet- and this obvious truism becomes all the more pertinent. Low sleep levels bring about a rise in cortisol in the body, a stress hormone that can lower mood and exacerbate existing symptoms of keto flu.

If you’re putting yourself at risk of the exhausting impact of keto flu, you should be doing everything you can to make sure that every other lifestyle factor is working in your favour as mitigation. Adequate sleep levels– seven hours or more per night- are crucial in this undertaking.

Much of the exhaustion caused by the ketogenic diet occurs during this keto flu period- the first few weeks, in which the stress of adaptation is making your feel rough as anything. Longer term issues may still occur with regards fatigue, though proper hydration, electrolyte replacement and adequate caloric intake should set you straight.

If you’re following a ketogenic diet- either as a beginner, or if you’ve been on it for a while- and you’re finding yourself becoming increasingly or periodically exhausted, try the tips listed above. One of them, or a combination, could be the secret you’re looking for to unlock your potential as you strive for ketosis.

Share your love
Avatar photo
James Dixon

James Dixon is a fully qualified personal trainer and award winning writer, with a decade’s worth of experience under his belt. Throughout his career, he has helped hundreds of people to meet their dietary and fitness goals, writing exercise and nutrition plans to suit any and every requirement.

Newsletter Updates

Enter your email address below and subscribe to our newsletter

Leave a Reply

Your email address will not be published. Required fields are marked *

Subscribe to Our Newsletter
Get Insider Tips Straight to Your Inbox!