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Keto Flu Symptoms

At the start of the keto diet, many people start to see symptoms of an illness develop called keto flu. Learn about the symptoms of keto flu and how our supplements can help you manage.
Keto Flu Symptoms

Who doesn't want better cognitive function, a healthier body, and more energy while also losing weight? The keto diet, which is short for the ketogenic diet, promises all this and more — but how does it work? Essentially, keto provides your body's energy using a different type of "fuel" than a standard diet. Rather than burning the glucose that comes from carbs, your body will rely on ketone bodies that it creates from fat. This requires you to cut out carbs like bread, cereals, pasta, and rice, as well as some fruits and vegetables. You then substitute in fatty foods like meat, butter, oil, and nuts. Without any carbs to burn, your body must turn to stored fats for energy.

Though it seems like a modern fad, the keto diet has been around for some time. In the 19th century, doctors recommended the keto diet to prevent conditions like diabetes. Then, in the 1920s, it became an effective treatment for epilepsy in medication-resistant children. Nowadays the keto diet is a widespread phenomenon that proponents claim can decrease appetite, trigger weight loss, and fight illnesses like diabetes [1].

What is Keto Flu?

While keto may seem like a dream diet, it's not without its problems. Within two to seven days of starting the keto diet, you may start to feel unwell or develop a few side effects. Some of the most common of these are headache, fatigue, brain fog, irritability, nausea, and constipation. Because of their similarity to a certain viral illness' symptoms, many people refer to this collection of side effects as the "keto flu."

These issues develop because of the substantial shift in your diet and the various nutritional changes and deficiencies that follow, though the exact mechanisms remain a mystery. Plus, keto flu doesn't affect everyone the same way. Some people are lucky and don't experience it at all! In this article, we'll discuss some of the most common keto flu symptoms, what causes them, and how you can manage the condition.

Keto Flu Symptoms


One of the signature symptoms of keto flu — and beginning a keto diet in general — is the keto headache. Several factors contribute to this irritating headache, which usually develops shortly after starting a keto diet for the first time. During ketosis, your body burns fat as its primary energy source. Unfortunately, this can dramatically drop your blood sugar levels as you shift from relying on glucose to ketone bodies [2].

Additionally, people tend to urinate more once their bodies enter ketosis because their bodies are depleting glycogen, which binds to water molecules [3]. This makes dehydration one of the most common side effects of starting the keto diet, and a common culprit for keto headaches. Beyond this, your body produces less insulin while on the keto diet because there's less of a need to process glucose. A drop in insulin levels can also affect electrolytes like sodium and potassium, triggering symptoms of dehydration [4].

Difficulty Sleeping

Sleep quality plays a massive role in your overall health and affects everything from your brain function to how well your heart operates. This makes the dreaded "keto insomnia" one of the more significant side effects of the keto flu. According to studies, keto insomnia is among the rarer symptoms but is often quite severe [5]. Experts have pointed to several potential triggers for this insomnia, though they haven't nailed down a direct cause.

There's a chance that you're hungry, but due to feelings of bloating or nausea, you just don't realize it. Alternatively, some studies indicate that fat-based diets provide more energy, which can contribute to less sleep and a higher risk of sleep disorders [6]. Some people also turn to new foods and beverages like bulletproof coffee, which could lead to higher caffeine intake than usual. In some cases, simply not feeling well can affect your sleep.

Foggy Brain

Though many people find that the keto diet helps with their brain function and overall sharpness, those new to the diet may instead discover that their thinking is sluggish or fuzzy [7]. This symptom, called brain fog, usually manifests as an inability to focus or concentrate, though you may also have memory issues or simply feel "off." It can be hard to nail down what causes brain fog, especially when following the keto diet. It could be due to dehydration, nutrient deficiencies, a lack of exercise, or not getting enough sleep. For more information on brain fog, take a look at our article on its causes and how you can boost your cognitive function.


Many keto beginners expect a boost in energy once they swap their diets, but the reality is that you usually have to go through a period of fatigue. Switching from burning carbs to burning fat for energy is a major metabolic change and it can take several days for your body to adjust [5]. The general drop in caloric intake and lack of certain nutrients may also be responsible. Additionally, other symptoms of keto flu, such as dehydration or difficulty sleeping, can contribute to a general feeling of fatigue and tiredness.


Though it is less of a side effect of keto and more an outcome from all of the keto flu symptoms, many people with keto flu feel irritable. Between the headaches, dehydration, lack of sleep, and nausea, it's no wonder that people might feel a little crabby. Some people also use eating as a way to manage their stress, which typically stops when they swap to the keto diet.


You might notice feelings of nausea once the keto flu sets in. Experts aren't entirely sure what causes it, but there are a few potential theories. Our bodies digest carbs easily and quickly, but it takes substantially longer to digest fat [8]. During the early days of the keto diet, this can lead to bloating and nausea as the body attempts to break down the greater volumes of fat. Because of this, bloating, nausea, and even vomiting are common side effects. Additionally, suddenly changing your diet may impact the gut microbiome, which is a complex system that can have dramatic effects on the body and how we feel.


A common mistake that many people make when swapping to the keto diet is not finding a new source of fiber. This, in combination with the uptick in fat consumption, can cause constipation. However, even an adequate source of fiber may not be enough for keto newbies. Some evidence suggests that suddenly cutting out carbs can stress your gastrointestinal tract, causing bowel issues like bloating and constipation [9].

How Long Does Keto Flu Last?

Keto flu can persist from several days to several weeks, depending on numerous factors. According to anecdotal reports, most symptoms of keto flu appear to improve within 30 days [5]. This length of time is essentially a transition period where your body transforms from relying on carbs to utilizing stored fats for energy. However, there are ways to drastically speed up your recovery process. Researchers found that the vast majority of keto flu cases could be resolved by addressing nutrient deficiencies that develop as a result of dietary changes.

Supplements Can Help with Keto Flu

As you might expect from having to cut out such a wide range of foods, partaking in the keto diet can cause several nutrient deficiencies if you're not careful. This can lead to issues like dehydration and brain fog, as well as more serious health issues like a loss of bone density or cardiac conditions. Keto diets are usually lacking in these vitamins and minerals:

  • Vitamin D
  • B Vitamins
  • Thiamin
  • Folate
  • Calcium
  • Choline
  • Sodium
  • Potassium
  • Magnesium

Finding dietary sources for these nutrients can be difficult, especially when sticking to a keto diet. One of the easiest ways to ensure that you're getting the vitamins you need while following a restrictive diet is to take a supplement or multivitamin that is keto-friendly. A high-quality supplement will not only address your nutritional deficiencies but also help alleviate the symptoms of keto flu, leaving you feeling refreshed.

Healthycell's Bioactive Multi

Bioactive Multi

Healthycell's Bioactive Multi provides a complete spectrum of essential vitamins and minerals, including those that your body may be missing while on the keto diet. It even offers you other integral nutrients that help combat symptoms of keto flu. For example, each serving of Bioactive Multi is bursting with thiamin, vitamin B12, zinc, and vitamin C, which help cut through brain fog and sharpen your cognitive function.† Plus, unlike many other health brands, Healthycell understands your dietary needs. Bioactive Multi contains less than half a gram of sugar and less than a gram of carbohydrates, so you'll never interrupt ketosis by taking the supplement.

Healthycell's Vegan Essentials

Vegan Essentials

Whether you follow a plant-based keto diet or a more typical one, our team of experts designed Vegan Essentials to fill the nutritional gaps that more restrictive diets often create. With nutrients like vitamin C, vitamin A, choline, and omega-3 fatty acids, Vegan Essentials boosts your energy levels, brainpower, and immune system function.† Plus, it contains all the fiber you need to fight issues like nausea and constipation, so you don't have to worry about searching for dietary sources that mesh with your diet. It can even help with dehydration by replenishing key electrolytes like magnesium. Like Bioactive Multi, Vegan Essentials also contains less than half a gram of sugar and less than a gram of carbohydrates, making it the perfect fit for any keto diet.

As a bonus, MICROGEL technology built into these supplements boosts your body's ability to absorb nutrients from both Bioactive Multi and Vegan Essentials by releasing tiny, ultra-bioavailable, soluble nutrient particles in your digestive tract. Plus, MICROGEL is much easier to swallow than traditional supplements. They are more natural too, without synthetic binding glues, fillers, or coatings found in most pills.

† These statements have not been evaluated by the Food and Drug Administration. This product is no intended to diagnose, treat, cure, or prevent any disease.

Dr. Giampapa is a world-renowned medical doctor, inventor, and surgeon specializing in anti-aging medicine. He recently received a nomination for the Nobel Prize for his groundbreaking stem cell research, as well as the Edison Award for the Healthycell nutritional supplement for cell health. He was also awarded the A4M Science & Technology award for his development of the BioMarker Matrix Profile – the first computer program to measure aging. Learn more about Dr. Vincent Giampapa.



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