From chapter 12 ("How to Beat the Keto Flu") from Dr. Don Colbert's new book, Beyond Keto
The keto flu is not a flu. Rather, it's a combination of non-life-threatening symptoms that feel like a flu. That's all. And for the most part, it's your body's reaction to shifting from a high-carb diet to a low-carb diet.
You could call it withdrawal if you want, but these symptoms are common to almost everyone starting on a keto diet. They often occur at the beginning right as you are trying to shift from sugar-burning to fat-burning.
During the shift, as you are purposefully decreasing the sugars, carbs, and starches and increasing the fat intake, there is often a gap where there is less-than-normal energy on hand to burn. It's like the doldrums, where there is no wind and the sailing ships are stuck. You have lowered your carbs to only 20 grams but have not shifted into ketosis so that you are burning fats effectively. You simply don't have enough carbs to maintain your energy needs.
But you can rest assured that these symptoms will eventually pass away, sometimes within minutes, hours, or days. Either way, they usually don't last long once you learn the simple solutions for keto flu.
The Keto Flu
Here is a collection of keto flu symptoms, many of which came from my patients over the years:
brain fog (example: locking your keys in the car)
lack of focus
Extra Help to Get Across
Everyone is different. For those who are healthy and it takes just a few days to shift into ketosis, they may not experience keto flu at all. Or the symptoms may be mild. For those who are obese, prediabetic, type 2 diabetic, insulin resistant, fighting cancer, or suffering from some other sickness, it can take several weeks (four to eight) to shift into ketosis. And the symptoms may be more pronounced and last for days or weeks.
For some of us, our bodies have been burning sugar as fuel for forty or fifty years, even seventy or eighty years! It's simply going to take a little time for the shift to happen. There are a lot of changes, reverses, and revisions involved in the process. It's not an instant process.
With that said, it does not mean you have to soldier on and press through, regardless of the pain. Yes, to a certain degree we all have to press through, but if there is an answer that eases the pain or speeds up the shift to ketosis, then let's do it!
Here are several things you can do to help yourself past any keto flu symptoms and into ketosis more quickly.
Add more salt.
We all have about 4 pounds of water that is retained in our bodies due to salt and insulin. It is there because of the high amounts of insulin our bodies use to balance the high-carb food intake. In other words, a high-carb diet causes higher insulin levels, which causes us to retain water.
But when you lower your carbs on a keto diet, this water is released, which is why you have about a four-pound weight loss the first week on a keto diet. Along with the water goes the sodium that has been retained due to the higher insulin levels. In other words, the lower insulin levels have a direct effect on the body initially.
Many of the keto flu symptoms are a direct result of low sodium. Thankfully, the answer is simple enough: add more sodium to your diet.
You can boost your sodium by
adding ½ to 1 teaspoon sea salt or Himalayan pink salt to a glass of water
adding 1 bouillon cube to a cup of warm water
eating a bowl of healthy, low-carb soup
eating salty pickled vegetables
salting your food more than usual.
Drink more water.
The second most likely culprit behind keto flu symptoms is dehydration. Interestingly, lack of water and low sodium cause almost the exact same keto flu symptoms, but it makes sense when you see how they are connected.
On a keto diet, now that insulin levels are lower, water is not retained as it once was. Because sodium is stored in the intracellular and extracellular fluids within your body, when your fluid levels go down, your sodium levels also go down.
You will need to drink more water, but don't overdo it. Why not? Because more water will dilute the sodium in your system (increasing the keto flu symptoms), and more water intake will cause you to go to the bathroom more frequently (and out goes the sodium), which may make things even worse. When you are thirsty, drink. That's the most practical middle ground when it comes to your fluid levels to prevent dehydration but also add back some salt.
Sodium is not the only electrolyte (a mineral that carries an electric charge) that can go low while your body is recalibrating itself. In addition to sodium, people may become deficient in magnesium, calcium, chloride, phosphorus, and potassium. In fact, 50-90 percent of people are deficient in magnesium.2
Water does not have these electrolytes, but you can get them from the foods you eat. Here is a list of electrolytes and foods that contain them:
potassium (in avocados, nuts, dark leafy greens, salmon, and mushrooms)
magnesium (nuts, dark chocolate, artichokes, spinach)
calcium (leafy greens, broccoli, seafood, almonds)
phosphorus (meats, nuts, seeds, dark chocolate)
chloride (most veggies, olives, salt, seaweed)3
Take psyllium husk powder.
During the shift from burning sugar for fuel to burning fat for fuel, there are several areas in your body where there is a lot of action taking place. The gut is one of those places.
One of the best calming agents for the gut is fiber in the form of psyllium husk powder. Your body needs at least 2 tablespoons of this fiber per day, but you need to work up to that amount. I suggest starting at 1 teaspoon once in the morning after breakfast and once after dinner before bed, slowly working up to 1 tablespoon or more twice a day.
Just because people are starting a keto diet does not erase these facts:
Only 5 percent of Americans consume enough fiber.4
Constipation usually worsens with age, and more than forty million adults in the United States (about 16 percent of the population) suffer from chronic constipation.5
Millions of people in the USA have acid reflux and take antacids, which usually increases constipation.6
What's more, several of the typical keto flu symptoms, such as diarrhea, constipation, dehydration, and gas, are helped by the psyllium husk powder.
The psyllium husk powder also helps you achieve your health goals because it makes you feel satisfied longer (thus controlling your appetite), slows digestion, normalizes bowel movements, increases insulin sensitivity, gives you energy, and improves your metabolism.
Add MCT oil/powder.
One supplement that needs to be part of your keto diet and eventual Mediterranean-keto lifestyle is MCT oil. MCT stands for medium-chain triglyceride, and it also comes in powder, liquid, or capsule form. I recommend the powder form of MCT oil because it is perfect for stirring into coffee or tea.
MCT oil is very effective at pushing you into ketosis. It's like a strong gust of wind that helps blow you out of the keto flu doldrums. With your coffee or tea, start with 1-2 teaspoons. Start low with MCT oil as it can cause loose stools. Slowly increase the amount, but I'd not suggest more than 1 tablespoon of MCT oil at a time. MCT oil tends to cause loose stools in many, but MCT oil powder is less likely to cause loose stools.
Moderate MCT oil consumption is a healthy addition to your daily routine. And as you begin a keto diet, it is especially beneficial because it helps propel you forward into ketosis. And once that occurs, MCT is more good fuel to your fat-burning fire.
Take exogenous ketones.
Though it sounds exotic, exogenous ketones are simply supplements of the ketone, beta-hydroxybutyrate, which your body makes when you are on a low-carb keto diet. They are ketone salts, including sodium beta-hydroxybutyrate, magnesium beta-hydroxybutyrate, potassium beta-hydroxybutyrate, and calcium beta-hydroxybutyrate. These really tend to pull most people out of keto flu, usually within thirty minutes to an hour.
These ketones, whether from your own body or as a supplement, efficiently and effectively raise your blood ketone levels so you start burning fat for fuel right away, and that means you are in ketosis.7 They also help control hunger, increase your energy levels, boost your mental capacity, and relieve keto flu symptoms.
As a supplement, these exogenous ketones are like MCT oil, only stronger. They can help you be in ketosis usually within the hour. I usually recommend exogenous ketones to people who are insulin resistant, prediabetic, have type 2 diabetes, or are obese, as their bodies typically need an extra boost to get over to ketosis.
Will the Keto Flu Return?
Experiencing keto flu symptoms once is bad enough, but will they ever come back? That's a good question, and the answer is maybe. Let me explain.
Once you reach ketosis and that has become your new normal, there are usually only two main reasons that you might feel those same keto flu symptoms again. The first reason is what you would expect: eating too many carbs. If you eat more carbs than your own level of fat-burning can handle, you will be bumped out of ketosis, and keto flu symptoms may return. Brain fog, lethargy, and feeling unfocused are most common.
You already know the solution to the problem: decrease your carb intake.
If you do eat more carbohydrates than your macronutrient levels allow (it's best not to), try to do it for dinner. Then you will usually sleep well. If you do it at lunch, you may need to take a nap in the middle of the day! Either way, the next day is a new day. Jump back into your planned keto diet routine.
The second reason that you may experience keto flu symptoms again is less expected: too much exercise. Our bodies burn glucose when running or during intense exercise. The problem is that your body is purposefully very low in glucose and your glycogen stores (stored in your muscles and liver) are probably depleted because you are burning fat for fuel. If there is not enough glucose on hand for intense exercise, your body will not like it.8
I experienced this first hand. After intense workouts, I would usually crash and need a thirty-minute nap. I thought something was wrong with me, but I had forgotten that short bursts of exercise (as is common in intense workouts, running, bicycling, high cardio training, or physical outdoor work) burn glucose. It's best not to do intense exercise until you reach your goal weight, then increase your carbs before your workouts.
The answer is to eat more carbs on the days that you do more intense exercise. For athletes, they simply need to eat more carbs on the days that they train.
Eating small to moderate amounts of sweet potatoes, beans, rice, and other healthy carbs are good before you do high intensity exercise. Learn to find the balance, and build that into your routine so you don't have a relapse of the keto flu.
Thankfully, the keto flu passes. It is not a permanent condition in the slightest. In time, it will be a distant memory.
For more information about Beyond Keto, check out DrColbertBooks.com.
1. Ryan, Simply Keto, 39; Cole, Ketotarian, 126; Tyler Cartwright, "What Causes Keto Flu? (AND 6 Keto Flu Remedies)," Drink LMNT, accessed September 13, 2021, https://drinklmnt.com/blogs/health/what-causes-keto-flu-and-6-keto-flu-remedies.
2. James J. DiNicolantonio, James H. O'Keefe, and William Wilson, "Subclinical Magnesium Deficiency: A Principal Driver of Cardiovascular Disease and a Public Health Crisis," Open Heart 5, no. 1 (2018): e000668, https://dx.doi.org/10.1136%2Fopenhrt-2017-000668.
3. Ramos, The Complete Ketogenic Diet for Beginners, 21.
4. Quagliani and Felt-Gunderson, "Closing America's Fiber Intake Gap."
5. Castaneda, "10 Causes of Chronic Constipation."
6. Stuart, "Acid Reflux Symptoms."
7. Axe, Keto Diet, 81.
8. Axe, Keto Diet, 54.
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