My Experience with Keto Flu: Symptoms and How I Got Through It
Posted by Mira on April 30, 2025
When I decided to start the carnivore diet, I made a quick switch from the Standard American Diet (SAD) to full carnivore. The transition wasn’t smooth—I experienced several uncomfortable symptoms commonly known as the "keto flu."
Keto flu is a well-known side effect of starting a ketogenic diet, and while it can be unpleasant, it's important to remember that it’s not a sign of failure or something to fear. It’s simply your body adjusting to a new fuel source—shifting from burning carbohydrates to burning fat.
In this blog post, I’ll share my personal experience with keto flu and how I got through it. For each symptom I encountered, I’ll explain why it happens and what helped me manage it.
Contents
Keto Flu Symptoms
1. Fatigue
I experienced fatigue as one of the most common symptoms of keto flu.
Why: This happens because the body is used to using carbohydrates for energy, and when we switch to a ketogenic diet, it needs time to adapt to using fat as its primary energy source. This transition can lead to a temporary drop in energy levels and feelings of fatigue.
Solution: Gradually add animal fats and butter to your diet to support the transition. If the fatigue becomes unbearable, you can temporarily reintroduce a small amount of carbohydrates to ease the adjustment.
Keep in mind: Once your body has adapted to burning fat for energy instead of glucose from carbs, the fatigue will disappear. You'll start to feel much more energetic—and this energy will be steady and consistent. That’s a good sign that you’ve entered ketosis.
2. Headaches
Why: When the body begins transitioning to using fat as fuel, one of the first signs you might notice is a reduction in belly fat within the first few days. This happens because in the absense of carbs the visceral fat around your organs is being broken down and converted into ketones. A portion of that breakdown includes water, which is then flushed out through urine—along with a significant amount of electrolytes (including sodium, potassium, and magnesium). When sodium levels drop, headaches can occur.
Solution: Place a pinch of high-quality salt (such as Redmond Real Salt, Light Grey Celtic Sea salt, or Himalayan salt) on your tongue, add a bit of water to your mouth, let the salt dissolve, and then drink it. Wait about 30 minutes. The headache should ease or disappear.
Keep in mind: Don’t overdo it. Too much salty water can lead to water retention. When the body senses excess salt, it holds onto water to maintain balance, which can cause bloating, swelling, and elevated blood pressure.
I made this mistake once—impatient to see results, I drank too much salty water. The next day, I experienced water retention. Fortunately, drinking more plain water helped flush out the excess salt and resolve the issue.
3. Racing or Irregular Heartbeat (Heart Palpitations)
During the first few days of starting the carnivore diet, I noticed that my resting heart rate—tracked by my Apple Watch—kept rising, and at times, I found it hard to breathe.
Why: Just like with headaches, this is often caused by electrolyte imbalances. A stable heartbeat requires a proper balance of potassium and sodium. When potassium levels drop, the heart has to work harder, which may result in a faster or irregular heartbeat. Potassium and sodium are two minerals that work together to maintain proper muscle function and heart rhythm.
Solution: Add electrolyte supplements that contain potassium. I use unflavored Hi-Lyte Keto K1000 Electrolyte Powder, which provides 1g of potassium per serving. You can also eat potassium-rich foods like avocados.
Keep in mind: Do not exceed 4g of potassium per day. Too much potassium can lead to hyperkalemia, a potentially dangerous condition. Symptoms may include muscle weakness, cramps, or even paralysis. If you notice any of these signs, stop taking the supplement and seek medical attention immediately.
4. Tense Muscles or Cramps
I didn’t experience many cramps like some others have reported, but I did notice tense muscles.
Why: Similar to headaches and heart palpitations, this is often due to electrolyte imbalances—specifically low magnesium levels. Magnesium plays a crucial role in regulating muscle contraction and relaxation. When levels drop, muscles may feel tight or even cramp.
Solution: Add electrolyte supplements that include magnesium. Hi-Lyte Keto K1000 Electrolyte Powder also contains magnesium. Alternatively, you can take magnesium glycinate, which is gentle on the stomach (unlike some other forms that may cause diarrhea). Eating more beef can also help, as it's a good natural source of magnesium.
5. Diarrhea
Why: When you drastically change your diet—such as switching to a carnivore diet—your gut microbiome also undergoes significant changes. The trillions of microbes in your digestive system help break down food, and many of them are adapted to fiber-rich or plant-based diets. Eliminating these foods can cause an initial imbalance as certain bacteria die off and others (better suited to a meat-based diet) begin to flourish. This transition period can disrupt digestion and often leads to diarrhea until a new microbial balance is established.
Solution: Give your body time to adjust—this phase usually passes within the first week or two. Stay well-hydrated, as diarrhea can lead to fluid and electrolyte loss. You may also want to add a pinch of salt to your water to help maintain sodium levels.
6. Black Diarrhea
I had this black diarrhea for a few days, often right after I ate a lot of fat.
Why: Black diarrhea, especially after consuming a large amount of fat, can happen, but it’s important to differentiate between normal changes and potential warning signs. When you consume a lot of fat, your digestive system might struggle initially to break down all of it, especially if your body is not yet adapted to a high-fat diet. The black color could also indicate the presence of bile or undigested fat.
Solution: Gradually increase fat intake to allow your body time to adapt. Try consuming animal fats or butter alongside lean meats, which can help ease digestion and prevent an overload of fat at once. Also, consider balancing your fat intake with digestive aids like bile salts if you continue to have issues.
Keep in mind: If the black color persists, it could also be a sign of gastrointestinal bleeding, and you should seek medical advice.
7. Insomnia
Why: During the initial transition phase, changes in hormones and metabolism—such as shifts in cortisol and insulin levels—can disrupt your natural sleep-wake cycle, leading to issues like insomnia or fragmented sleep. A very low intake of carbohydrates may also influence the production of melatonin indirectly, potentially making it harder to fall asleep. Additionally, consuming too little fat (the body’s primary energy source on keto) might leave you under-fueled at night, possibly affecting sleep quality.
Solution: Maintain a consistent sleep schedule and develop a relaxing bedtime routine. Limit screen exposure before bed and create a comfortable, calming sleep environment. If your fat intake is on the lower side, consider increasing it gradually to support overall energy balance. Personally, I found that grilling and eating lamb fat in the evening helped me sleep better.
