You've decided to try the keto diet. The low-carb, high-fat diet can be great for decreasing body weight and might give you a boost in endurance performance, but the body often needs a little bit of time to adapt to using fat as its main energy source. Often, there are some symptoms involved during this period of adaptation.
These symptoms are called the "keto flu," a commonly-experienced set of side-effects associated with carbohydrate withdrawal. Reported symptoms include: mood swings, irritability, fatigue, and dizziness. This may sound like withdrawal symptoms from substance abuse; interestingly, recent studies have compared the effect of carbohydrates (particularly sugar) on the brain to that of addictive drugs like cocaine.1 And these symptoms from the keto flu can last anywhere from a day to a couple weeks.
Shortsighted dieters may allow keto flu knock them off the diet altogether–but after a period of metabolic adaptation, the body adjusts to the change and ultimately reaches a state where it's primarily burning fat as a fuel source. Typically, fat is a largely-stored, and largely untapped, energy source for the body. During this transition phase however, there are several ways to reduce, prevent or manage symptoms of the keto flu. We'll discuss some of the most common symptoms, the science behind them, and offer some solutions to nascent keto dieters.
What Causes Keto Flu?
Carbohydrates typically make a big contribution to the body's energy needs. When carbohydrates are restricted in the diet, the body responds through a series of changes to transition from using glucose for energy to using fat, and also ketones. This gear-switching is a good thing; but it's also the reason for keto flu. First, blood sugar drops and causes hypoglycemia, which is low blood sugar < 55 mg/dL.2 Second, changes occur in other bodily systems that alter electrolyte, water and hormone levels–this can lead to dehydration from following the ketogenic diet.
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Falling Blood Glucose
With the physical consequences of sudden carb removal, we must first understand that our body generates energy using two main mechanisms: glycolysis (converting glucose to energy) and beta-oxidation (converting fat to energy).
Complying with a low-carb ketogenic diet means forcing the body to switch from using carbs as energy (via glycolysis) to predominantly using fats as energy (via beta-oxidation). After a period of adaptation, the body usually also begins generating energy from the breakdown of ketones (via a process call ketolysis) instead of glucose. This switch occurs because the body breaks down fatty acids into ketones (ketogenesis) so the brain can use them for fuel.3
What happens when the body hasn't yet learned to burn fat and produce ketones? That's where hypoglycemia comes it. The result is a temporary energy deficit in the brain due to low blood sugar. Remember: this is a transient period of adaptation. The ease with which you can switch to using fats and ketones as energy varies by person, depending on a mix of genetics and habitual diet; some individuals demonstrate a greater metabolic flexibility than others. These lucky people experience far fewer symptoms or experience the flu for a shorter duration.
Research has found the same pathways of the reward system in the brain are activated in both high-carb foods and cocaine or heroin. Both cause the release of dopamine (a "feel good" hormone). Regular carb consumption modifies gene expression and dopamine receptor availability in that reward system over time. This translates to a need for even more carbohydrates to have the same effect on those brain receptors. So the sudden removal of carbohydrates can lead to withdrawal symptoms, both physical and psychological.
Electrolyte Imbalance and Dehydration
Electrolytes are the minerals in the body that are derived from salts, e.g. calcium, potassium, magnesium, chloride, and sodium. Electrolyte levels, controlled by the kidneys, are crucial for maintaining bodily functions such as heartbeat regulation and muscle contraction.4 B
Why does the ketogenic diet cause electrolyte imbalances? The key reason is that dietary carbohydrate restriction reduces insulin release. Insulin signals cells in the body to absorb glucose in the bloodstream, but it also signals the kidneys to reabsorb/store more water.5Lower insulin levels (as a result of decreased carb intake) means the kidneys now store less water. This results in dehydration and the flushing out of electrolytes in the process.6Changes also occur in parts of our body where carbohydrates are stored, such as the liver and muscle. Stored carbohydrates (glycogen) trap three grams of water per gram of glycogen—so when these stores are depleted on keto, the associated water is also lost. This further contributes to the reduced amount of water and electrolytes in the body.
Hormonal Stress Response
A poorly-formulated ketogenic diet (one too low in calories or deficient in micronutrients) can trigger a starvation response in the body, thus raising levels of cortisol (the body's stress hormone). 7 Cortisol release is the body's attempt to protect the brain by raising blood sugar, trying to compensate for the now low blood sugar caused by carb reduction. If excess cortisol is released, stress response and blood sugar stability can become deregulated.
Thyroid hormones are also something to consider, as they have several functions in the body including the maintenance and regulation of carbohydrate/energy metabolism. The T3 (or euthyroid) is the most biologically active form of the hormone, and is linked to dietary carb consumption. T3 levels have shown to decrease in response to carb restriction below a certain threshold (which varies from person to person).8 This can result in fatigue or difficulty focusing through the adaptation period. Conversely, lowered T3 is also hypothesized to bring several benefits if thyroid function is normal. This includes improving longevity and preserving muscle mass.
While discomfort may result during the transition, you can rest assured that lowered T3 does not appear to be indicative of hypothyroidism in humans with normal, healthy thyroid function.9
Avoid These Things If You're Experiencing the Keto Flu
As with any type of sickness, your body will have some physical or mental limitations. If you're not feeling 100%, you shouldn't push your body. While these flu-like symptoms should be temporary, maybe wait until the symptoms subside before doing these things.
Strenuous Physical Activity
After an adaptation period, the body will begin to use ketones and fat as fuel (instead of carbohydrates). Since the body stores far more fat than carbohydrates, tapping into those fat stores for energy will pay dividends for athletes—especially endurance athletes. But before you keto-adapt? Best to stay away from difficult physical exercise. You may be experiencing upset stomach, fatigue, muscle cramping, or brain fog. You are not Michael Jordan. Saturday morning pickup basketball is not you "flu game."
For high-intensity exercise, carbohydrates are the most readily-available and effective fuel for the body. Since you're now carb-depleted, it's best to avoid this type of exercise, giving the body some time to fat adapt. Though, regardless of fat adaption, carbohydrates will also be the primary fuel source for these types of exercises. A study of obese individuals showed a decrease in physical exercise capacity during the first week of low-carb dieting.10 But the study also saw performance benefits in the final week of keto dieting (which lasted four weeks).
Trying low-intensity exercise instead. Things like yoga or walking might help, but the bottom line is to take it easy during this period of adaptation.
Staying Up Past Your Bedtime
Again, any type of sickness calls for more rest. But since you may already be experiencing fatigue as a result of the keto flu, proper sleep is necessary.
Cortisol levels can increase due to a lack of sleep, possibly making keto flu symptoms worse than they already are. A study done on servicemen showed that cortisol levels can increase with sleep deprivation, and mental health can also be affected by lack of sleep.11 Luckily, there are many different ways to try and improve sleep and sleep quality.
An hour of screen-less time before bed might help, as screens can negatively impact sleep.12 Blue light emitted from our devices tricks the brain into thinking it’s daytime and we need to be awake, decreasing our natural melatonin. Creating an optimal sleep environment might also be beneficial. Try things like blackout curtains, a cooler temperature setting in the bedroom, a quality mattress—all of these might encourage better, more restful sleep.
And if none of these work? Try Yawn, from HVMN. Yawn is our non-habit forming sleep aid. It combines the sleep-inducing effects of melatonin and L-Glycine to help get the body and brain in recharge mode. Studies of ingredients in Yawn showed that participants fell asleep seven minutes faster and upon waking, studies demonstrated an overall 3% improvement in sleep efficiency.13,14
All calories are not created equal. Different foods have substantially different metabolic and hormonal effects on the body. So what you eat (and how calories are expended) can change how much you eat and whether those calories are burned or stored. Some people on a ketogenic diet will restrict calories if they're not seeing results, but usually, calorie restriction shouldn't be a worry while on keto.
Some dieters may get extremely hungry during the adaptation period, but they shouldn't think too much about overconsumption of calories just yet. Other dieters may feel nauseous and eat less as a result of the keto flu itself. This likely won't last; eventually, keto may lead you to consume less overall, as you become more able to be satiated on increasing fat consumption in your diet (as this systematic review pointed out).15
The first week of keto will be a drastic shift in carbohydrate consumption levels. Try to consume enough healthy fats to make you satiated. Avocados, cheese, fatty fish, nuts, eggs—all of these are great sources of healthy fat and can be consumed until you're full. Still, be mindful of your eating. Don't overeat simply because you're a cheese-a-holic.
Solutions to Common Symptoms
Symptoms of the keto flu vary from person to person. But there are easy solutions one can leverage to help combat these symptoms.
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In ketosis, headaches can occur due to electrolyte imbalance and dehydration. With low insulin levels, the kidneys go into a diuretic state, so potassium, water, and sodium are excreted. A silver lining here is the loss of excess water weight with the decrease of stored water in the body. Conversely, dehydration and electrolyte imbalance are the reasons for many keto flu symptoms. Monitor salt and water intake while on keto, and consider supplementing with electrolytes.
The necessity of electrolyte management is underestimated on low-carb diets. Even if macronutrient intake is monitored correctly, maintaining the correct balance of electrolytes often goes overlooked. The cause of electrolyte imbalance? Usually, it's eating too few mineral-rich fruits and vegetables when transitioning to the keto diet. Removing salt-laden, processed foods means the body is now cut off from the sodium or electrolyte sources it once had. While many keto dieters are wary of increasing sodium intake and raising blood pressure, removing processed foods from the diet and reducing carb intake already has a significant blood pressure-lowering effect.16
Supplementing other minerals is also vital. Magnesium is important for the body, contributing to muscle and nerve function, blood glucose control, and protein synthesis.17 Potassium also helps proper functioning of the heart, digestion and muscle function.18 Foods rich in potassium and magnesium include tomatoes, avocados, salmon, nuts, leafy greens, and animal protein. Bouillon cubes, homemade stocks (like beef broth or chicken broth), and sea salt are all rich in sodium and minerals. One should consume these to minimize the risk of headaches.
Cramping is the most common sign that electrolytes are out of balance.
The common mistake is not drinking enough water to compensate for water during the keto transition phase, which may result in low blood pressure and constipation, other than just cramps.6 Causes for cramps can also be caused by low potassium or low magnesium. Animal protein (and even bone broth) is an excellent potassium source, and the juices from cooking meats should be retained for this purpose. For magnesium, seek out leafy greens; the darker the better!
This may be a result of the digestive system transitioning on keto. Any dramatic lifestyle changes impact gut microbiome, inevitably altering bowel movements. Dehydration can worsen constipation (because of the increase excretion of fluids by the kidneys). Eliminating high-carb fruits and vegetables (starchy vegetables specifically) can also reduce dietary fiber and contribute to constipation.
Eat plenty of fiber-rich fruits and vegetables, exercise and drink plenty of water every day. But be warned–eating excessive fiber can also lead to constipation, so finding a balance is necessary. That balance is something that can only be determined from personal experience.19 MCT or medium-chain triglyceride oils are a solution. This may help to relieve constipation, as fat can help push bowel movements through. Finally, take care to ensure your calorie intake is adequate, as not eating enough calories can also contribute to constipation.
Some keto dieters experience bad breath, discerningly fruity or similar to nail polish remover. Besides the odor, this might be positive—it's an indicator of a body in ketosis. However, it's usually reported to go away within a week or two, once the body adapts to the new metabolic state it is in. Maintaining good oral hygiene, increasing water intake, and using gum or breath freshener can help mask or reduce the smell in the interim while the body is still adapting.
Fatigue, Low Mood, and Cravings
As the body adapts to ketosis, a decrease in energy levels and weakness are often reported, which can impair physical performance. Fatigue can last anywhere from three days to weeks as the body prepares new enzymes for the diet.
The tiredness may be caused by thyroid hormone and cortisol changes; the body is trying to compensate for the lowered carbohydrate intake by releasing more cortisol, which raises blood sugar. The possible result? Irritable mood and reduced sleep quality. Since cortisol levels are likely to reduce again when the body becomes keto-adapted, these symptoms should be temporary. To lessen fatigue, water and mineral intake should be carefully monitored (and likely increased). B vitamins, particularly B5, are vital for helping with fatigue and lethargy. It's crucial to eat enough calories from fat for sustenance, as being under-fueled can also cause fatigue.
Removing glucose from the diet can affect mood and cause cravings. Replacing foods you crave with low-carb alternative or removing food "triggers" can help reduce the psychological (and thus physiological) symptoms of carb withdrawal. While there are low-carb or keto-friendly recipes for some of your favorite treats, many people who have successfully transitioned to the ketogenic diet say that just going “cold turkey” on sweet-tasting things and refined sugars helps to get rid of those nasty cravings sooner.
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Keto flu systems are often transient, disappearing completely after keto-adaptation.
Lifestyle determines length and severity of the keto flu for the individual, with symptoms likely greater for individuals who ate a high-carb diet previously. Even during transition, the symptoms can be alleviated if treated smartly. A well-formulated low-carb diet can progress without significant symptoms if the common mistakes of poor mineral intake, lack of fiber, electrolyte imbalance, and dehydration are addressed.
Avoid falling into the common trap of assuming your body is not suited to the low-carb diet after just a few days, and instead, carefully monitor water and mineral intake particularly for the days/weeks it takes your body to adapt. Have a look online for some keto support groups if you have questions, and perhaps think about trying exogenous ketones, like HVMN Ketone. Exogenous ketones can give you an energy boost as beta-hydroxybutyrate without the need to take in carbs.
Have you experienced keto flu symptoms while transitioning onto the keto diet? Tell us about your experience in the comments below.