Chances are, if you’ve heard of keto, you’ve heard of keto flu. However, you may not know much about it. If that’s the case, you’ll find all you need to know right here.Keto flu’s symptoms don’t usually last very long, and the benefits of a ketogenic diet are so numerous that it’s worth dealing with the transition time. Fortunately, there are some simple things you can do to make it go as smoothly as possible. But first, you need to understand what keto flu is. 


Keto flu is not caused by a virus nor by ketosis. It is a collection of symptoms caused by carbohydrate restriction. The symptoms can mimic some flu symptoms, which is how it got its name. Common symptoms are: 

- Headache 

- Fatigue 

- Brain fog 

- Dizziness 

- Loss of strength or endurance 

- Muscle cramping or soreness 

- Irritability 

- Sugar cravings 

- Stomach issues (less common) 

- Insomnia (less common) 

The symptoms can start within 2 days of carbohydrate restriction, and they can range from a few to most of those listed. For many people, they will only last a week or two. Others may find it takes up to a month to make the transition. Either way, the symptoms will start stronger and gradually go away, and you can do things to mitigate their effects. 

Several things can affect how easily the transition goes for you. Your previous diet is a big one. If you have already restricted carbohydrates from the government recommendations, your body will be more accustomed to using fat. That would make the transition easier. Your metabolic flexibility will also influence how much you are affected by keto flu. 

Some people are “metabolically inflexible,” which means they don’t switch between fuel sources very well. It seems that genetics, the number of mitochondria that are available and insulin sensitivity all play a role in your flexibility. While a family history of diabetes and insulin resistance seem to be an indicator, there is not really a way to tell in advance how metabolically flexible you are.


There are a few contributing factors to keto flu, and they are all caused by restricting carbohydrate consumption. When you understand what happens, you will be able to mitigate the effects – or even prevent them entirely. 


Keto is a diuretic diet, which means that water is flushed from the body. When that happens, sodium is also lost. Since sodium, magnesium and potassium need to be in balance with each other, low sodium can lead to the other electrolytes being eliminated to restore balance. 

Insulin, or rather the lack of it, is responsible for this loss of fluid and sodium. When carbohydrates are consumed and glucose is absorbed, insulin tells the kidneys to hang onto water and sodium. 

Each gram of glycogen (stored glucose) needs almost 3g of water for storage, so the water needs to be there or else the glucose can’t be stored. 

When insulin levels drop, the kidneys are free to release excess water and sodium. That means that while you eat a ketogenic (low-carb) diet, your insulin levels will always be pretty low, which leads to the diuretic effect. Also, as you use up the stored glycogen, the storage water will be released, so you could lose up to ten pounds of water weight in the first week on keto. 

Headaches, muscle cramps, dizziness and fatigue are all related to water and electrolyte loss. 


Eating a ketogenic diet causes a starvation response in the body. You aren’t actually starving, but the effect is mimicked by restricting carbs, and the body needs to switch to fat oxidation (fat “burning”). Starting a keto diet creates some stress in the body, which causes a short-term rise in cortisol. 

When cortisol is high, you could be cranky and have trouble sleeping. Long-term high cortisol levels also tend to cause weight gain, but that won’t be an issue here. Studies on men have shown that low-carb diets cause free testosterone levels to drop and cortisol levels to rise, and that exercise combined with low-carb diets did the same. 

One thing to keep in mind, though, is that those were short-term studies not done on those who were used to a low-carb diet. You can reasonably expect the hormone levels to normalize once you are adapted. In the meantime, you might experience irritability and difficulty sleeping. 


Since carbs are restricted, the body has to switch to a fuel that it isn’t really used to using. That means the enzymes aren’t in place in sufficient numbers for fat metabolism, and they’ll need time to increase. While they work on that, your body won’t be able to provide very steady energy levels. Low energy can lead to fatigue, dizziness, low physical performance and brain fog. Fortunately, there is a solution to this.


Here are the key things to do to make the transition as easy as possible. 


With all the water loss, you need to make sure to drink enough. It is all too easy to get dehydrated and experience headaches and fatigue, but more severe dehydration can lead to poor physical and mental performance. There’s no need to drink gallons, but you should drink about 90 ounces. To help your body hold onto some of it and get some sodium replacement in, add a pinch of sea salt to a glass of water before you drink it. 


Sodium, magnesium and potassium are very important and need to be kept up to par for you to feel your best. Remember that sodium loss will cause loss of the other two as they try to maintain balance. 


Sodium is easy to replenish by salting your food to taste with a good-quality salt. Sea salt contains important trace minerals and is not cut with dextrose (a sugar) like iodized salt can be. You can add a pinch of salt to your water as well, which is the first thing to do if you are experiencing headaches – get water and salt into you ASAP. 

While a “low-sodium diet” is touted as healthy, that’s a bit misleading. We need sodium for many bodily functions, and it is important to replenish it when on keto. It’s diets that are high in processed foods (which are high in sugar, starch and unhealthy fats) that need to reduce sodium intake. 


Roughly half of Americans don’t get enough magnesium. Low magnesium can cause muscle cramps and spasms, headaches, difficulty sleeping and more. Some keto-friendly foods with good magnesium levels are dark leafy greens, pumpkin seeds, avocado, sunflower seeds, fatty fish, cocoa powder (and very dark chocolate), almonds and cashews. Aim to get 300 to 400mg per day. 


The U.S. recommendation for “adequate” potassium is 4.7g per day, and it seems that 98 percent of the population doesn’t reach that. Low potassium can cause headaches, fatigue, muscle cramping, irregular heartbeat and more, but too much potassium is also bad. 

Beet greens, spinach, avocado, salmon, zucchini, mushrooms, cauliflower and beef are good keto-friendly sources of potassium. You aren’t at all likely to get too much potassium from foods alone, but it is a risk when supplementing. Always follow the recommended dosing when taking a potassium supplement. 


It can be difficult to keep track of the minerals you get through eating, and some people don’t have the time or the inclination for that. A good keto-specific supplement can simplify this for you. If you find it difficult to get enough magnesium and potassium through food sources, try supplementing to avoid the symptoms. 


The low-energy part of the keto transition can be helped by getting enough of the right kind of fat. Eating enough fat is important for energy levels during the transition, and getting some medium-chain triglycerides (MCTs) is a very good idea. 

MCTs go from the small intestine directly to the liver for energy usage and will be converted to ketones for use right away. Coconut oil and MCT oil are two great sources of MCTs that will help give you a boost while your enzyme levels build. 

If you pick up an MCT oil, try to get one that is high in C8; the powdered form is also good to prevent gastric distress. C8 has the biggest energy benefit of the MCTs other than C6, but C6 is not widely available for extraction. 

Another choice is a product called exogenous ketones. Since you’ll be consuming ketones directly, you’ll skip the conversion step. That makes the energy available a bit more quickly. Like MCT oil, too much too quickly can cause some gastric distress. 


Not sleeping enough will create additional stress on your body, so aim to get 7 to 9 hours per night. Getting enough sleep can actually decrease cortisol levels, so make it a priority. Take a nap during the day if you feel the need and have the option. 

If you are having trouble falling asleep, spend 30 minutes before bed in a darker room and don’t look at any screens (tv, computer, phone, etc.). Artificial light can negatively affect your circadian rhythm, which has numerous health consequences, but it also suppresses production of a sleep-inducing hormone called melatonin. 

Low magnesium levels can also cause sleep problems, but supplementing is proven to improve melatonin levels, sleep efficiency and sleep time. If you are having difficulty falling asleep, make sure your magnesium intake is up to snuff. 


While your body is adjusting to its new fuel source, your energy levels are lower. This is not a time to do HIIT (high-intensity interval training), CrossFit or any other high-intensity workout. If you want to exercise (which is a good idea but not necessary to benefit from keto), keep it simple and light. Working out too hard will raise your cortisol level, which is already elevated, and it may cause you to be fatigued or dizzy or even to pass out. 


Maybe you have even fewer enzymes for fat metabolism or are metabolically inflexible. Perhaps the stress is just very difficult and all the above tips aren’t working well enough for you. There’s an alternate plan you can follow. 

Instead of dropping carb consumption all the way down to below 20g net carbs, decrease carbs more gently over a longer period of time. It will take longer to get into ketosis, but it can be easier on your body. 

For the first week, try to eliminate all soda, juice and sugars (including natural sugars). In the second week, don’t eat bread, chips, pasta or any refined grains or grain products. In week three, get rid of the grains altogether and the starchy veggies too. In the final week, reduce your fruit intake. At this point, you should be getting all of your carbs through vegetables and limited amounts of low-carb fruits and be able to stay below 20g net carbs.


While there are several possible symptoms when starting a ketogenic diet, the prevention strategies are simple. Drink water, replenish your electrolytes, don’t do hard workouts, get enough fat (including MCTs) and get enough sleep. They aren’t hard things to do, though they can be hard to remember if you are experiencing brain fog. If you find yourself stuck in keto flu or feeling off, check back here and make sure you aren’t missing anything. Read our keto guide to get started on the road to better health!

  • Comments
    1 out of ...