You’ve decided to try the keto diet. The low-carb, high-fat diet can be great for performance and decreasing body weight, but the body needs a little bit of time to adapt to fat as an energy source. Often, there are some symptoms involved during this period of adaptation.
It’s called the “keto flu,” a commonly-experienced set of side-effects associated with carbohydrate withdrawal. This may sound like withdrawal 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 Reported symptoms include: mood swings, irritability, fatigue, and dizziness. It 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 will reach a state where it’s burning fat as a fuel source, a largely-stored, but for many, a largely untapped bodily energy source. 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.
Science Behind Keto Flu
Carbohydrates are the body’s preferred energy source. When those are restricted, the body responds through a series of changes to transition from using glucose (stored carbs) for energy to using fat. 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 In response, the body changes both the fuel it uses for energy and how neurons in the brain function. Second, changes occur in other bodily systems that alter electrolyte, water and hormone levels–this can lead to dehydration from following the ketogenic diet.
Falling Blood Glucose
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 using fats as energy (via beta-oxidation). After a period of adaptation, the body usually begins to generate 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 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 and low blood sugar. Remember: this is a transient period of adaptation. Switching 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 individuals may show 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 withdrawn 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
Why does the ketogenic diet cause these imbalances? Carbohydrate restriction, and thus insulin release. With a lower carb intake, insulin levels drop.
Insulin signals cells in the body to absorb glucose in the bloodstream, and signals the kidneys to store more water.5 Lower 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.6 Stored carbohydrates (glycogen) trap three grams of water per gram of glycogen–so this also causes a depletion while on keto, further contributing 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 (stress hormone). 7 Cortisol release is the body’s attempt to product 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. They have several function, 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 The result may be 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.9
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 (and thus weight loss) with the decrease in stored water. 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 weary 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.10
Supplementing other minerals is also vital. Magnesium is important for the body, contributing to muscle and nerve function, blood glucose control, and protein synthesis.11 Potassium is also helps proper functioning of the heart, digestion and muscle function.12 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 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 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.13 MCT or medium-chain triglyceride oils are a solution. This may help to relieve constipation, as fat can help push bowel movements through. Finally, care should be taken 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 oder, 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, 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 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.
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, consider careful monitoring of 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.