The ketogenic diet involves changing your metabolism from favoring glucose from carbs to fat and ketones for energy.
And with this big metabolic change comes some potential side effects. Things like headaches, fatigue, and nausea can pop up in the first week or so of the keto diet. A phenomenon referred to as the keto flu.
The good news is — it’s temporary.
Keto flu is most prevalent when you’re transitioning into a ketogenic state. Once you’re fat-adapted, the symptoms disappear. Still, it’s good to know what you’re up against, plus how a few simple tips and tricks may help prevent keto flu symptoms.
What Is the Keto Flu?
The keto flu is a temporary collection of flu-like symptoms you might experience when trying to enter ketosis for the first time. It goes away once you become fat-adapted — within the first week or so of eating a ketogenic diet.
It happens because your metabolism needs time to adjust to running on fat instead of carbs.
Your body burns carbohydrates (glucose) for energy by default. When you drastically reduce your carb intake — like on a low-carb ketogenic diet — your body depletes your glucose stores and starts burning fatty acids for energy.
This metabolic switch can be tough on your body, hence the flu-like symptoms.
It’s not uncommon for keto beginners to experience the keto flu when they first reduce their carb intake. Common symptoms include:
- Stomach pain
- Brain fog
- Dizziness or confusion
- Diarrhea or constipation
- Muscle cramps
- Muscle soreness
- Lack of concentration or focus
- Trouble falling or staying asleep
- Sugar cravings
- Heart palpitations
- Low energy levels
Symptoms usually occur within the first day or two of starting your new diet, and the severity and length of symptoms vary from person to person.
Some people don’t experience it at all, while others could experience it during the first week or longer.
Either way, the symptoms shouldn’t last more than a couple weeks and should go away once your body is adapted to burning fat for fuel.
There are four potential causes of keto flu:
- Becoming fat-adapted or keto-adapted
- Electrolyte loss and dehydration
- Withdrawal from carbohydrates and sugary foods
- Lack of micronutrients
#1: Keto Adaptation
Your body has two primary energy processes:
- Glycolysis: burning glucose for energy
- Beta-oxidation: burning fat for energy
Keto-adaptation means adjusting to the process of beta-oxidation, or burning fat for energy.
Those with less metabolic flexibility are more likely to experience keto flu symptoms as their body adjusts to using fat for energy.
Genetics also play a role. Some people are naturally more capable of handling the energy switch.
Takeaway: Adapting to ketosis is the main cause of the keto flu.
#2: Electrolyte Imbalance
When you radically decrease the amount of high-carb processed foods you were used to eating on the standard American diet (SAD), your body starts to lose water quickly.
This is because all the glycogen (stored glucose) you’ve been accumulating on a high-carb diet is bound to water in your body (each gram of glycogen is stored with 2–3 grams of water).
When you go keto, your cells use up all that glycogen, which means that your water weight gets flushed out.
So now you’re losing both fluids and important electrolytes, which then causes dehydration and electrolyte imbalances.
This combo can cause flu-like symptoms like headaches, fatigue, and aches and pains until everything becomes balanced again.
During your transition, it’s crucial to replenish your stores by increasing your water intake.
You’ll also want to add back the minerals you’re losing (i.e., electrolytes such as sodium, magnesium, and potassium).
This will help ease the transition and ensure you’re still getting an optimal amount of the nutrients you’re losing through your urine.
Properly hydrating with extra water and electrolytes will help you prevent and reduce your keto flu symptoms.
Takeaway: Losing water and electrolytes when you’re transitioning into ketosis can trigger flu-like symptoms.
#3: Lack of Micronutrients
Another common trap many beginner keto dieters fall into is not eating enough micronutrients.
When you cut out certain vegetables, fruits, and grains, you need to eat adequate amounts of keto-friendly foods to get the micronutrients you were getting from those foods.
For example, if you drastically reduce your carb intake and start eating primarily eggs and cheese to stay keto, you’re at risk of creating nutrient deficiencies.
To combat this, it’s essential to eat a wide variety of nutrient-rich keto foods and stay healthy during your transition.
A diet high in these foods will cover your bases:
- Fatty cuts of grass-fed meat
- Coconut and cacao butter, as well as coconut, olive and avocado oil
- Nuts and seeds (including nut and seed butter)
- Poultry, fish, shellfish
- Veggies like alfalfa sprouts, broccoli, cucumber, cabbage, olives, spinach, Swiss chard, eggplant, asparagus, cauliflower, Brussels sprouts, spaghetti squash, etc.
- Full-fat organic dairy
If you’re short on time or always on the go, supplementing with micronutrients may be an easier option so you’re not missing out on essential vitamins and minerals.
Each scoop of this Perfect Keto Micronutrient Powder comes packed with pure, plant-sourced nutrition from 26 different fruits and veggies, helping you get a healthy dose of these important micronutrients without having to physically eat almost 30 healthy foods.
It’s also free of sugars, cheap fillers, and additives so you’ll never have to worry about any questionable ingredients kicking you out of ketosis.
Foods to Avoid on a Keto Diet
Speaking of, there are certain foods you should avoid on a ketogenic or low-carb diet. You’ll want to steer clear of packaged foods since these often contain chemical ingredients, which can prevent you from reaching and maintaining ketosis, thus prolonging your keto flu. Other foods to avoid on keto include:
- Grains like wheat, barley, oats, rice, quinoa, rye, buckwheat, and sprouted grains
- Beans such as kidney, black, pinto, lima, and chickpeas
- Most fruits, especially tropical ones like bananas, oranges, pineapples, papayas, and mangoes as well as apples and grapes
- Starchy vegetables including sweet potatoes, carrots, parsnips, potatoes, and corn
- Cane sugar, raw sugar, and high fructose corn syrup, as well as sweet syrups like honey, agave, and maple syrup
- Milk and low-fat dairy
- Factory farmed, conventional meat options such as grain-fed or highly-processed meats, farm-raised fish, etc
- Unhealthy vegetable oils like soybean, canola, corn, grapeseed, peanut, sesame, sunflower, and safflower
- Processed foods
- Artificial sweeteners
- Sweet alcoholic and non-alcoholic beverages
Takeaway: Micronutrient deficiencies can trigger the keto flu. Eating a nutritious ketogenic diet is key.
#4: Carbohydrate Withdrawal
Some studies suggest that sugar affects the brain in a way similar to addictive substances like heroin or cocaine[*] — consuming sugar provides the “feel good” hormone known as dopamine.
That’s why carb withdrawal can contribute to the keto flu. You’ll see this in the form of mood swings, irritability, cravings for sugar, and other adverse symptoms.
This is especially pronounced in people who eat more processed and refined carbs and sugars. People in this category also have more trouble adapting to fat burning, therefore they have a harder time losing weight.
But this doesn’t mean you should abandon ship.
If you’re experiencing these negative withdrawal symptoms, it’s a sign your body is getting closer to reaching ketosis and you just need to power on.
At this point the keto benefits really start to kick in.
Once the sugar and carbs are finally out of your system, you’ll start to lose weight and realize that after the initial discomfort, the keto benefits are well worth it.
Takeaway: Carb withdrawal can worsen keto flu symptoms, particularly if you’re used to eating high-carb, processed foods.
If you’re already experiencing the keto flu, take comfort in knowing this is temporary and there are things you can do to reduce or even eliminate symptoms during your transition to ketosis.
If you suspect you’ve been hit with the keto flu and you’re past the point of prevention, below are some things you can do to get rid of it.
#1: Stay Hydrated
As mentioned earlier, drinking extra fluids and staying hydrated should be your top priority.
The water loss that occurs at the beginning of a ketogenic diet needs to be replenished. The more often you do that, the easier the transition will feel.
Drink plenty of water throughout the day to help reduce symptoms like headaches, fatigue, or nausea that are often caused by dehydration.
Here are some easy ways to accomplish this:
- Keep a reusable water bottle near you, filled at all times so you can drink it wherever you are.
- Always drink when you feel thirsty, but try to catch it before thirst strikes.
- Drink most of your water during the day so you’re not waking up in the middle of the night for a trip to the bathroom.
Takeaway: Drink more water to get rid of headaches and fatigue.
#2: Replenish Electrolytes
On top of getting enough water, your next focus should be balancing your electrolytes.
You may not have considered your electrolytes before keto unless you were exercising vigorously or had too much to drink the night before.
The transition from using carbs for energy to using fat for energy will flush important electrolytes from your system.
And each person loses electrolytes differently.
Keep these general guidelines in mind to mitigate a potential imbalance:
- Increase your sodium intake. This will help counteract the water loss that happens when starting a keto diet and replenish sodium. Get your sodium from Himalayan pink salt instead of regular table salt.
- Supplement with magnesium. Low magnesium levels can lead to depression and insulin resistance, among many other issues, so it’s important to include this mineral in your diet. Some rich food sources of magnesium include hemp and pumpkin seeds, cooked spinach, halibut, cashews, salmon, macadamia nuts, avocado, and dark chocolate[*][*][*].
- Eat potassium-rich keto foods. Potassium is another key mineral that should be on your radar but probably isn’t. This electrolyte is involved in heartbeat regulation, muscle cramping, energy production, bladder control, and body temperature[*]. If you’re feeling any issues connected to these areas, consider adding more potassium-rich foods like avocado, Brussels sprouts, mushrooms, zucchini, and pumpkin seeds to your keto meal plan.
- Eat calcium-rich keto foods. Broccoli, leafy greens, chia seeds, sardines, and salmon are all packed with calcium. And bone health isn’t calcium’s only job. It’s also vital for blood clotting, muscle contractions, and good cardiovascular health[*].
- Take an electrolyte supplement. If you need instant relief, taking an electrolyte supplement will help replenish your levels faster than foods can. Check out the vitamin and mineral supplement guide for more information.
Takeaway: Keep your minerals in check, or take an electrolyte supplement to balance your electrolytes.
The type of exercise you do matters during your transition from burning carbs to fat.
Your exercise performance may temporarily suffer while your body is adapting to a higher fat and lower carb intake.
So while you probably won’t hit a personal record during this time, that doesn’t mean you should stay in bed.
Getting light exercise 2-3 times per week can help make your body more efficient at switching between carbs and fats for energy (i.e., metabolic flexibility), which helps decrease keto flu symptoms more quickly[*].
Low-intensity aerobic exercises — such as walking, swimming, or practicing yoga — are smart during this time since your body already uses fat as its primary energy source when performing this type of exercise.
Once your body gets through the transition, you should be able to resume your normal exercise routine.
Learn more tips on exercising while on keto.
Takeaway: Exercising can boost metabolic flexibility and get you over keto flu quicker.
#4: Increase Fats
Since your body is no longer getting its energy from carbohydrates and sugars, it needs plenty of fat and protein for fuel.
This means you’ll need to make sure the calories you used to get from carbs are partially replaced by eating plenty of keto-friendly fats.
Some of those include:
- Grass-fed butter or ghee
- Heavy cream
- Coconut oil
- MCT oil
- Palm oil
- Cacao butter
- Extra virgin olive oil
- Avocados and avocado oil
- Goose fat
- Lard and bacon fat
- Pecans, macadamias, and walnuts
- Flaxseed, sesame, and chia seeds
- Fatty fish
Increasing your fat consumption while reducing your carbohydrate intake will help ease your transition since you’ll be pushing your body into using fats for energy.
Supplementing with MCT oil can also help you beat the keto flu by increasing your ketone levels, which can shorten your transition period.
If you find the keto flu persists longer than a week, re-evaluate your macros. You might still be eating too many carbs and not enough healthy fats.
Sometimes people think they’re transitioning into ketosis when in reality hidden carbs might be holding them back.
Takeaway: Make sure you’re reducing carbs and eating more keto-friendly foods to transition to ketosis.
#5: Take Exogenous Ketones
Remember, one of the reasons you may have the keto flu is because your body is trying to create and use ketones for energy.
One way to help mitigate keto symptoms is to add exogenous ketones, or ketone salts, to your morning routine.
These energy molecules are the same ketone bodies your body naturally produces, in supplement form.
Supplementing will flood your system with ketones so you get some of the benefits of being in ketosis before you’ve even burned through your glycogen stores.
You can use exogenous ketones during your initial transition or anytime you want a quick boost of energy and mental clarity.
Takeaway: Supplement with exogenous ketones to help get keto-adapted more quickly.
If you’re just starting the keto diet and want to prevent the keto flu altogether, it can be easily avoided by following the steps below.