The keto flu is a set of symptoms that happen as you start the keto diet. Here’s a detailed look at what it is, the symptoms, and how you can help ease it.
Over the last few years, the Keto Diet has rocketed to international fame as the “superstar” of weight- and fat-loss diets.
It’s in the news, on talk shows, in magazines, pretty much everywhere you look! You can’t avoid talk about “Keto this” and “Keto that”—the vast majority of it is hugely positive.
But what you might not hear about is the negative (and trust me, it exists).
Specifically, one of the worst side effects of this new diet: the Keto Flu.
If you’re wondering what the Keto Flu is and how it could affect your life, you’ve come to the right place.
Below, we’ll take a deep dive into this bizarre condition that sets in as a result of the Keto Diet and learn everything you need to know about it.
Let’s jump right in.
Keto Diet – Overview
Before we get into talking about the Keto Flu, we first need to explore the diet that can cause it: the “Ketogenic Diet”, better known as the Keto Diet.
To put it simply, the Keto Diet is a low-carbohydrate, high-protein, high-fat diet.
Carbohydrates are your body’s primary energy source (thanks to our modern carb-heavy diet), but the Keto Diet slashes carbs and increases fat intake in order to shift the body into a “ketogenic” (fat burning) energy production mode.
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When you switch to a low-carb, high-fat diet, your body starts to burn a lot more fat for energy, so it becomes more efficient at burning fats.
- Better fat-burning. Your body burns not only the fat you eat, but also your stored fat. This leads to fat loss (the BEST kind of weight loss)!
- Reduced appetite. Not only is fat better at satiating your appetite than carbohydrates, but it also maintains steadier blood glucose levels, which reduces the insulin spikes and crashes that trigger strong appetite/cravings.
- Lower calorie intake. High consumption of protein and fats (in combination with cutting carbs) has been proven to lead to lower overall calorie intake.
- Active water and weight loss. Not only will the Keto Diet help you to get rid of the “water weight” that’s always the first to go, but it will help to eliminate excess fat weight—ergo, the “healthy” kind of weight loss.
- Slimming down. Your waist, belly, buttocks, thighs, and arms will be thinner because you’re effectively burning the fat stored there.
- Lower cholesterol and triglycerides. This drastically reduces your risk of cardiovascular disease and metabolic syndrome.
- Lower blood pressure. Also a great contributor to better heart health!
- Therapeutic for brain disorders. Low-carb ketogenic diets have been proven effective for treating conditions like epilepsy (especially in children), and may one day offer solutions for conditions like Parkinson’s and Alzheimer’s.
Wow, that’s some pretty clear-cut proof that the Keto Diet really can work for you, right?
All pretty great reasons to pull out the keto cookbook and start searching for new Keto recipes, right?
Well, slow your roll there!
Before you dive head-first into the Keto deep-end, it’s important to understand the other side of things—the potential drawbacks.
Specifically, the Keto Flu.
What are the Symptoms of Keto Flu?
The Keto Flu presents different for everyone, but it tends to look and feel a lot like your average summer flu.
Symptoms will likely include (though perhaps not be limited to):
- Foggy brain
- Increased hunger
- Digestive upset/discomfort
- Sleeping difficulties
- Decreased exercise performance
That doesn’t sound fun, does it?
What Causes the Keto Flu?
No one really knows.
I’m sure that’s not the answer you wanted to hear, so let me explain…
No “official” studies have been conducted on this collection of symptoms resulting from the Keto Diet. Go to PubMed, and you’ll find many “consumer mentions of the Keto Flu”, but no scientific tests or analyses to quantify it.
That’s because the Keto Flu is really just a collection of symptoms people on the Keto Diet experience while their bodies are shifting from carb-based energy to fat-based energy.
During the transition period—usually starting sometime in the first 2-7 days of the Keto Diet—your body starts to “freak out” a little because it’s not getting enough of its usual energy source (carbs).
It can produce some energy from the fat it’s got floating around in its system, but the lack of carbs causes it to start misfiring—producing the above-mentioned symptoms.
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The problem is: everyone’s body reacts differently to the diet, so there’s no single collection of Keto Flu symptoms that can be listed. And each individual will experience it differently.
Some people will experience sleeping troubles but none of the other symptoms, while others will struggle with digestive issues and low energy, but never get headaches or brain fog.
Really, when it comes to the Keto Flu, experts  have more questions than answers.
It could be a number of things going haywire in the body during the transition period:
- An immune system reaction
- Some underlying detoxification factor
- Changes to the gut microbiome
- All of the above and more!
At the end of the day, though, all that matters is that the Keto Flu is real (for the vast majority of people who go on the Keto Diet) and the symptoms can be unpleasant while they last.
How long does the Keto Flu last?
Again, because the underlying cause of the Keto Flu isn’t clearly established, there’s no official diagnosis possible.
Anecdotal evidence from the many Keto dieters who have endured these symptoms report  that typically the Keto Flu will clear up within a week of onset, though some people experience them for longer.
The symptoms will usually only last for as long as it takes your body to adapt to the new fat-burning paradigm.
Once the change is “locked in” and your internal energy-producing mechanisms have switched to turning fat into fuel rather than carbs, the Keto Flu symptoms should clear up and you’ll be back to your old, happy, healthy self!
How to get rid of keto flu?
When it comes to “treating” the Keto Flu, the only real solution is to endure.
Or, put in the words of the great poet Robert Frost, “The only way out is through.”
Your body needs time to adapt to its new fat-burning state, so you’ve got to stick it out through the symptoms.
The human body is a truly remarkable adaptogenic mechanism that can quite literally transform itself on a cellular level to accommodate a wide variety of changes . In other words–your body will adapt!
If you can persist and not give up on the diet for the first week or so (despite the pesky flu-like symptoms), you’ll come out the other side a lot better for it, and your body will be in peak fat-burning state.
The good news is that there are some things you can do to manage the symptoms:
- Drink lots of water. And I mean LOTS! 4-5 liters per day should be your minimum. Water can be surprisingly effective at helping to regulate your appetite, reduce symptom severity, and even encourage faster adaptation to the diet. (See also: How Much Water Should I Be Drinking on the Keto Diet?)
- Take a painkiller. While there are no viral or bacterial infections causing the symptoms, you may find that a painkiller helps to reduce the severity of your headache, nausea, vomiting, or digestive upset.
- Consider a sleep aid. If you’re struggling to sleep at night during the Keto Flu, a sleep aid—like Valerian root, melatonin, or Ashwagandha—could make a difference over the week or two it takes your body to adapt.
- Eat more often throughout the day. This will help to combat increased appetite and may prevent nausea and digestive upset. Fortunately, there is a long list of excellent keto-friendly foods to help you attack the diet while keeping your taste buds happy.
- Eat more colorful veggies. They will have some carbs—enough that they help to “stabilize” your carb-starved body without overdoing it.
- Try some of the latest crop of keto pills on the market. If you are impatient and want to power through the flu, there are supplements (Keto Charge is one that I’ve tried and recommend) that help you “skip” the flu stage and get into keto faster. Keto pills are a proven way to help power through the symptoms that are inherent with carb withdrawal.
- Supplement properly. There is some promising research that shows various supplements for keto can help achieve ketosis faster, including MCT oil, multi-vitamins, and more. While supplements won’t replace proper dieting, they can help speed you through the worst of the adaptation phase.
What matters is that you stick with the Keto Diet and power through, no matter how terrible you feel.
Be patient, and know that once you come out the other side, you’ll be happy you persevered.
The Bottom Line
Yes, the Keto Flu is real, and it can make the Keto Diet a bit more of a hassle than you might like.
After all, no one wants to suffer headaches, nausea, vomiting, and other symptoms when they’re already struggling to make better eating choices and adapting to a new diet.
But, as you’ve seen above, the Keto Flu isn’t a real sickness, and it won’t cause any long-term harm or impairment. It’s just your body’s manifestation of its struggles to adapt to burning fat instead of carbs.
After all, you want your body to be in that fat-burning state!
The more effectively you burn fat, the easier it will be to eliminate the stored fat around your midsection, thighs, glutes, and the backs of your arms.
If you can endure the Keto Flu for a short period of time, the long-term gains in weight loss and improved health will be well worth any amount of suffering you might experience!
More Keto Guides and Resources
Keto Charge — A Keto Pill That Actually Works (Review). Curious if Keto Charge can help you get into ketosis faster and achieve your weight loss goals? Read on for a full review, including key features, and see if it’s right for you.
Keto Custom Plan – An Athlete’s Full Review. Is Keto Custom Plan right for you? Read this detailed review to find out what it’s like, the pros and cons, who should get it, and much more.
7 Best Drinks You Can Have on Keto (And Which Ones to Avoid). The keto diet is a great way to lose weight and improve health. But getting into ketosis can be tough. Here’s a look at the best keto-friendly drinks (and which ones to avoid) to help you master the ketogenic diet.