Carb-Flu: What Is It And How to Beat It

What is Carb-Flu exactly?

Maybe it's your first few days or weeks cutting out sugar, starches and processed foods. It's quite possible you are yet to feel the glowing effects of a Low Carb lifestyle that everyone has been talking about. In fact, you may be feeling pretty crappy right now. Read on!

“Carb-flu” or keto-flu”, as it’s been dubbed, is not an actual virus at all, but it’s a very real thing. The name comes from the flu-like symptoms that resemble a nasty, lingering cold. Carb-flu is a constellation of symptoms. It includes headaches, weakness, fatigue, irritability, difficulty concentrating, insomnia, constipation and muscle cramps and is linked to the early stages of embarking on a Low Carb diet. At this point, many people give up on their new eating regime – feeling low is a real motivation killer. Yet, understanding what’s happening to your body and, more importantly, what to do about it, is key to overcoming these symptoms and moving forward to a whole new world of health.


What causes Carb-Flu?

Many metabolic changes take place when you first cut down on carbs. Insulin levels drop, along with blood glucose, causing a host of knock-on effects. Perhaps the most important is how we use energy.

Energy comes primarily from glucose and from fat - either the glucose and fat that we eat, or the glucose and fat that we store in our bodies. In the modern world, most people eat a carb-heavy diet, with 50% - 60% (or even more) of total calories coming from carbs. Here's an important point to understand – carbohydrates (except fibre) are chains of glucose molecules. There are other molecules in carbs, such as fructose and galactose, but the predominant one is glucose. So a carb-heavy diet IS a glucose-heavy diet. Our bodies prioritize the incoming glucose when making energy. If you eat both glucose and fat together, your body uses the glucose first and stores the incoming fat for later.

On a Low Carb diet, the amount of incoming glucose is dramatically reduced. With your body not getting the glucose it’s used to, it MUST turn to fat in order to meet energy demands – this is a good thing. It’s exactly what you want. But, like a factory that hasn’t worked for a while, it takes time to adapt to these changes, and it’s not always a smooth transition.

The second important metabolic change on a Low Carb diet is the way your body regulates sodium and fluid. There is a word called “natriuresis” which means sodium excretion. On a Low Carb diet, natriuresis occurs and your kidneys excrete more sodium than with a regular diet. Again, this is completely normal. But along with the loss of sodium is the simultaneous loss of water. And if sodium isn’t replaced sufficiently, potassium gets dumped too, resulting in a lower electrolyte status – both sodium and potassium are important electrolytes.

As your body adapts to a lower carb diet, sodium regulation improves, but it is particularly acute when starting out. People notice how much they pee. The first few kilograms are lost rapidly. Although this is heartening, it’s mainly water loss, often accompanied by lower blood pressure – less fluid in your arteries, less blood pressure. Also a good thing!


With that in mind, here are 3 things that you may be experiencing in the early stages of going Low Carb along with some simple remedies to help you through:


1: The Hungry Brain

On a regular, carb-centric diet, your brain runs 100% on glucose. But unlike other tissues and organs in your body, such as your heart, your brain can’t use fat directly. So when glucose is low, it isn’t able to use fat to make up the difference in energy. Luckily, our bodies have adapted to this state over hundreds of thousands of years. During much of human history, food was scarce. Cavemen had no grocery stores. We have evolved a clever mechanism to cope with a low food / low glucose environment. How do we do it? Basically, fat is converted by your liver into another energy molecule called a ketone. This is where the term “ketogenic diet” comes from. And incredibly, ketones are an excellent and easily usable fuel for your brain. People with dementia often have clearly noticeable improvements in cognitive ability when ketone levels go up. Ketones also do other remarkable things, like reducing epileptic seizures and lowering inflammation, but that’s for another blog.

Now, in order to make ketones, there is, once again, a timing issue. When a person switches from higher carb to lower carb, the enzymes and processes to make ketones take some time to up-regulate. Remember the sleeping factory analogy? During the adaption phase, our brains are literally hungry for energy. And just like when we are sick, we feel lethargic, unwell, unmotivated and often have a headache. After a period of time, which could be days for some, and a couple of weeks for others, our livers begin churning out ketones and our brains consume both fuels - glucose and ketones – to power themselves. At this point, people often feel super-energised, and report a sharpness and mental clarity that they haven’t felt before.

The ability to switch quickly and effortlessly between burning glucose and fat, including making ketones efficiently, is called metabolic flexibility. Many leading doctors are extolling the virtues of metabolic flexibility as an important state for overall health and well-being.


2: Electrolyte Deficiency

When going Low Carb, it's important to pay special attention to your electrolyte intake. We explained above about the rapid sodium and water loss in the early stages of Low Carb. People quickly find themselves short of electrolytes and mildly dehydrated. This also contributes directly to lethargy, inability to concentrate, headaches, muscle cramps, and sometimes constipation.

On top of shedding sodium, a Low Carb diet also means a much lower intake of processed foods which contain lots of sodium. Have you ever looked at how much sodium is in breakfast cereal or potato chips? So, not only do we lose sodium, but we often aren’t getting enough through food anymore - a double-whammy. Over time, your body will regulate some of the sodium losses and hold onto sodium better, but the early period of Low Carb quickly leads to an acute electrolyte shortage, which is a major contributor to carb-flu.


3: Diarrhea

The assumption is that lowering one's carb intake and consuming less fiber places us at risk of becoming constipated, but in truth the opposite is often true. An increase in fat and artificial sugar consumption can temporarily disrupt digestion and cause diarrhea. Thankfully, like keto breath, keto diarrhea is not a permanent issue and will pass as the body adjusts. However, as with any bout of diarrhea, there is a risk of becoming dehydrated. The loss of fluids and bowel disruptions can culminate in heart palpitations, cramping and a general feeling of malaise.


Here’s a list of Carb Flu prevention tips:

  1. Give it time. Transitioning your fuel system from mostly carbs to mostly fat may not happen overnight. Remember, it may take several days, or more, to comfortably make ketones, providing the super-fuel for your brain.
  1. Mind your macros. Eating Low Carb signals to your cells to burn body fat and produce ketones. But if you eat too many carbs, you’ll likely have trouble adapting. You don’t want to get stuck in no-man's land where you’re eating too many carbs to make ketones, but not enough to satisfy your brain’s voracious appetite for glucose. That’s why it’s essential to closely watch your macros, especially in the early stages.
  1. Taking MCT oil may help in the production of ketones. MCT oil is a clear, tasteless liquid that comes from coconut oil. It is easily absorbed and converted by your liver into ketones. So 1 – 2 tablespoons per day may make a big difference to how you feel. Start off with half a tablespoon and increase over a few days until you get to 2. This will avoid any GI distress. The foundation of bulletproof coffee is MCT oil and butter for this very reason.
  1. Most Importantly, get in your electrolytes! To prevent electrolyte deficiency and improve your hydration, eat a diet rich in sodium, potassium, magnesium and calcium. This can be accomplished by salting your food with a high quality salt like Oryx Desert Salt, drinking bone broth and of course topping up regularly with a keto-friendly electrolyte drink like Revive.


Co-written by Jess Mouneimne and Mark Myerson

Jess is a certified health coach, certified strength and conditioning coach and professional MMA athlete. Mark is the co-founder of Revive Labs and a certified keto nutrition and diabetes coach.