Feeling not okay after starting the Carnivore Diet? Brain fog, muscle cramps, headaches? That’s Carnivore Flu—your body adjusting to a no-carb diet. This guide explains every symptom, why it happens, and how to recover quickly with real science-backed solutions.
The Carnivore flu, one of the most common Carnivore Diet side effects, is a temporary set of symptoms that occurs when your body switches from burning carbohydrates to burning fat.
It’s similar to Keto flu, but since the Carnivore Diet has fewer carbs than Keto (almost zero), the symptoms can be a bit more intense.
When you drop carbohydrates, your body goes through four major changes, which are the main causes of Carnivore flu.
These changes trigger symptoms like brain fog, headaches, fatigue, muscle cramps, and digestive issues. But don’t worry—it’s all part of the process.
Let’s start by breaking down each of these changes.
Learn More: 30-Day Carnivore Diet Meal Plan PDF (Downloadable File)
For most of your life, your body has relied on glucose (sugar) from carbohydrates as its primary energy source. When you suddenly remove all the carbs, your body panics a little.
It has to switch to burning fat (ketones) for energy, which doesn’t happen overnight. While the brain tries to switch between these energy sources, it may find it hard to work as well as before because it’s used to the energy from glucose.
This can cause:
A study on the ketogenic diet found that cognitive function is temporarily impaired during the first few days of carb restriction [1].
But don’t worry. After about one week, your brain learns how to use ketones and gets back on track.
When you stop eating carbohydrates, your insulin levels go down. As a reaction, your kidneys push out sodium and water, causing dehydration and mineral loss.
That’s why you may experience:
Studies on low-carb diets show that when electrolytes are not balanced, you feel tired and experience muscle issues. Losing sodium, potassium, and magnesium can lead to feelings of weakness, headaches, and even heart palpitations [2] [3].
If you have been on a high-carbohydrate diet, your gut bacteria have been using fiber and plant foods. When you remove those, your microbiome has to adjust.
This sudden shift can cause:
Research shows that dietary changes significantly alter gut bacteria [4]. The good news is that your gut will adapt to digesting meat efficiently, and many people experience improvements in digestion in the long term.
Insulin, cortisol, and other hormones swing as your body tries to learn a new way of eating. This can lead to:
A study on low-carb diets found that hormones are usually regulated within a few weeks, which means better energy and metabolism [5].
These major changes cause a series of symptoms we know as Carnivore flu, which we’ll learn about below. We’ll also learn ways to speed up the recovery from these symptoms.
Learn More: Carnivore Diet Results: #1 Way To Get Faster Results!
When you have brain fog, you can’t concentrate. It is like your brain is working slowly, so you think slower and feel tired and mentally lazy.
This happens because your brain is used to glucose (carbs). When you remove carbohydrates, it needs time to switch to ketones (fat). This temporary energy gap makes you feel mentally foggy.
Studies on low-carb diets found that cognitive function temporarily declines during the adaptation phase but improves once the body fully shifts to fat-burning [6].
To fix it, you can eat more fat to actually feed your brain and make it work faster. You can also give it some time. Brain fog clears in 3–7 days as ketones become the main energy source.
Carnivore flu headaches cause a dull, throbbing pain and get worse when standing up. It feels like you are dehydrated. If you went to a beach on a hot summer day, you know how it feels!
This happens because when you cut carbohydrates, your insulin drops. This makes your kidneys flush out sodium and water, which causes dehydration and headaches [7] [8].
Just add salt to your food because sodium stops dehydration. Drinking more water or bone broth helps you refill lost minerals and balance electrolytes.
These symptoms of Carnivore flu include sore, stiff muscles, random leg cramps, and weakness when moving.
When your body flushes out sodium, potassium, and magnesium, your muscles don’t work as smoothly as before. This leads to cramping and soreness [9].
Eating potassium-rich meats (beef, pork, salmon, organ meats), taking magnesium supplements (200–400mg daily with doctor’s approval), and drinking plenty of water are good ways to avoid muscle soreness and cramping.
Digestive issues can include either too frequent or not frequent enough bathroom visits, bloating, gas, discomfort, or even nausea.
Changes in diet, especially shifting from high-carbohydrate, high-fiber diets to high-fat ones, change gut bacteria within days to weeks [10] [11].
You can ditch these digestive issues by eating fattier cuts of meat because fat helps digestion. You can also drink water to help stool consistency. Even if you don’t do any of these, your gut will get back on track within 1 or 2 weeks.
Learn More: Carnivore Diet Meal Ideas + The Best Carnivore Diet Recipes
Low sodium and dehydration caused by electrolyte imbalances and lack of enough water drop blood pressure, causing dizziness and mood swings.
You can simply add salt to your food and drink more water to get rid of these symptoms.
When you cut carbohydrates, your body enters a ketosis fat-burning state, which increases acetone production. This can cause bad breath and dry mouth.
You can simply fix these symptoms by drinking more water or chewing sugar-free gum.
Dehydration and mouth breathing during ketosis can dry out the throat, causing
a scratchy and sore throat.
Drinking more water can help fix this, too. You can also use a humidifier at night.
Cravings are very common in almost all diets. When starting the Carnivore Diet, your body is used to sugar and carbohydrates; that’s why it can trigger you to eat sugary foods.
You just need to keep yourself busy to forget about cravings and let them pass, or you can eat more fatty cuts of meat because they keep you full.
Cutting or minimizing carbohydrates reduces blood volume, making your heart beat faster to compensate. Drinking water and using more salt can help with rapid heart rates.
But if you have any kind of cholesterol issues or underlying heart problems, consult your healthcare provider before doing anything else.
Although these Carnivore flu symptoms can irritate us, the good news is that they won’t last long!
Carnivore flu will not last forever, from 1 day to 3 weeks tops, depending on your body and previous diet.
Studies on keto adaptation show that, on average, most people adjust within 1–2 weeks [12].
Please note that not everybody experiences Carnivore flu and symptoms, and their severity varies from person to person, so don’t generalize.
There are also some hacks you can use to speed up the recovery process.
Learn More: 35 Best Carnivore Snacks to Add Variety to Your LowCarb Diet
Transitioning from high-carbohydrate diets to all low-carb diets, such as Keto and Carnivore, can cause similar symptoms during the adaptation phase. But Carnivore flu can show a bit stronger symptoms.
Although Keto flu and Carnivore flu are almost the same, Keto flu can be easier because the Keto Diet still allows some carbs, so the transition is easier.
On the Carnivore Diet, carbs are completely gone, making the adaptation harder but faster. You can compare these two kinds of flu in the table below.
A smart way to handle Carnivore flu symptoms is to think of it as a carb detox period! Your body has been using carbohydrates for a long time, and suddenly, you want it to switch to fat and protein.
This transition can cause flu-like symptoms, but it is temporary. Once your body gets fat-adapted, they are all gone, and you can enjoy the health results of the Carnivore Diet.
