Ketogenic diet enthusiasts love talking about how great they feel eating loads of fat and very few carbs. (No more brain fog! Zero sugar cravings!) What they might not mention? Going from a regular diet to a keto diet can temporarily cause some pretty unpleasant side effects.
We’re talking about keto flu-a cluster of flu-like symptoms that many newbies experience in the early days of adopting a ketogenic diet-and it’s not exactly fun. Whether you’re thinking of committing to a keto way of life or you’re already on the keto bandwagon, there are a few things you should know about the keto flu.
What is the keto flu? What are the symptoms?
Keto flu is a group of side effects that hit most people when they first switch from a higher carb diet to a ketogenic one. Many of them are similar to what you might feel like when you have the actual flu (hence the name). Keto flu symptoms typically include things like:
- Bad breath
- Weakness or fatigue
- Headache
- Nausea
- Muscle cramps
- Diarrhoea or constipation
- Skin rashes
- Mood swings
Why the heck does it happen? Normally, the body uses glucose—or sugar—as its main source of energy. When you cut your carbs below 50 grams per day (the typical threshold for a ketogenic diet), you enter a metabolic state called ketosis: Instead of burning carbs for fuel, your body begins burning ketones—an alternative fuel source that the liver makes by breaking down fat. In turn, this can make you feel run down.
That sounds awful. How long does the keto flu last?
Ketosis is pretty different from what your body is used to, and this onslaught of symptoms is its way of dealing with carb withdrawal—and adapting, explains ketogenic diet expert dietitian Kristen Mancinelli. “It takes a while, usually a week or two, for the metabolic machinery to shift to fat-burning mode. And you’ll feel pretty crummy while the transition is happening,” she says.
Keto flu symptoms can start to kick in within a day or two of adopting a ketogenic diet, Mancinelli says. If you recently cut your carbs below 50 grams daily and soon notice that you feel downright awful, you’ve probably got a case of keto flu.
That’s not to say everyone starting out on a keto diet ends up wholly incapacitated for days. “You might find that you fatigue more quickly or that exercise seems harder than normal,” says nutritionist Ginger Hultin. Your body might also have an easier time transitioning (read: fewer symptoms) if you were already eating a relatively low-carb diet, Mancinelli explains.
Is keto flu dangerous? Do I need to call my doctor?
Adopting a keto diet for the short term is generally considered safe, and any symptoms you might experience will typically clear up within a couple weeks, Hultin explains. (The jury’s still out on how eating this way might impact your body long-term.)
When you're on the keto diet, you need to drink more fluids than normal to avoid dehydration. That said, it’s a good idea to work with a doctor or registered dietitian before you start eating keto—and continue to check in with them while you adapt to your new diet, recommends diet expert Dr David Nico. Planning ahead can help you steer clear of nutritional deficiencies that can strike when you cut most carbs out of your diet. And doing so might also help minimise your keto flu symptoms.
For instance, working with an expert can reduce the risk for dehydration—which can make keto flu symptoms like headache, cramping, nausea, and fatigue worse. Drastically slashing carbs causes the body to excrete a higher volume of water and electrolytes, so you may need to drink more liquids and eat more salt to stay adequately hydrated, Mancinelli explains. How much more is different depending on things like your activity level and age, but a pro can help determine the right amount for you.
Is keto flu contagious?
While influenza is a virus that’s spread by close contact, keto flu isn’t something you catch. You’ll only experience symptoms if you enter a state of ketosis, and it’s not contagious.
Is there anything I can do to avoid keto flu?
Sorry, but probably not. Ketosis affects some people more than others, but there’s a good chance you’ll notice at least some side effects as your body adjusts to a (nearly) carb-free diet. The good news? There are a few steps you can take to keep things as pleasant as possible:
Stay hydrated
Remember, your water and electrolyte intake needs to go up on a keto diet, and dehydration can exacerbate many keto flu symptoms. There’s no hard and fast recommendation for how much water keto dieters should be drinking, Nico says. But in general, you should be sipping enough so that your urine stays clear or pale yellow. As for electrolytes like sodium? A dietitian can help you figure out how much more you should be having and the best places to get it. If you're feeling sick and can't see a nutritionist right away, consider mixing a low-carb electrolyte drink into your water.
Don’t push yourself
Stick with light exercise like walking-or take a break if you’re really pooped. “It may be best to take it easy and give your body time to adjust,” Hultin says.
Stick to your guns
Your symptoms will clear up as your body gets used to burning fat as fuel-so don’t confuse it by splurging on a bowl of pasta. “If you aren’t vigilant about sticking with your keto diet, you’ll never fully transition,” Mancinelli says.
The bottom line: The keto flu is temporary and common among keto diet newbies. Consulting with a nutritionist before starting the keto diet may help ward off uncomfortable symptoms. If you already have keto flu, listen to your body, take it easy, and make sure you stay adequately hydrated to ease the symptoms.
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