Is Carb Flu Really A Thing?

Photographed by Alexandra Gavillet.
When people are looking for ways to eat healthier, they often just decide to quit eating carbs, which doesn't really make sense at all. For starters, some of the tastiest healthy foods out there happen to be rich in carbs, and more importantly, carbs are vital macronutrients for human beings. But people still do it, and if you start Googling what it's like to stop eating carbs, you might come across something that some Paleo advocates have dubbed the "carb flu."
Basically, people claim that when you cut carbohydrates from your diet, it can cause a slew of symptoms, including a pounding headache, muscle soreness, fatigue, and general fogginess. Carb flu can last about a week, but once you get over that hump, people say you'll generally feel better and it will all be worth it. Apologies, but carb flu is not really a medical condition — or something worth "riding out" — it's a sign that your body isn't getting the energy it needs to function.
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Here's the deal: Carbs are your body's main source of energy, the Mayo Clinic explains. When your body digests carbs, it turns sugar and starch into simple sugars, and then glucose, which is how it gets energy. "Every cell, from the brain, to the organs, to the skeletal muscle runs on glucose, which is a simple carbohydrate that can be efficiently processed for energy," says Cara Harbstreet, MS, RD, LD, of Street Smart Nutrition. Carbs fuel your body for normal growth, development, and metabolic processes — but they also help power your day-to-day activities, like moving, Harbstreet says. So, you can see how denying your body of all carbohydrates would cause some issues.
When you extract your body's energy source, you're essentially "running on empty like a car with no gas in the fuel tank," Harbstreet says. Your body has to grasp to source energy from other stored sources, like fat or protein, she says. "There can be a delay as the body shifts metabolic processes to generate glucose from the liver or from stored fat," she says. "In the meantime, it's not unexpected that someone would struggle with irritability, fatigue, and otherwise feeling lethargic and tired." While cutting carbs won't give you a viral infection like the flu, it will make you feel pretty terrible.
If you've stopped eating carbs anyway, and are now experiencing the symptoms of carb flu, what should you do? Probably start eating some carbs again, Harbstreet says. "If these symptoms are the result of a drastic change in what you’re eating, it’s a loud and clear message from your body that it’s asking for something," she says.
Carb flu is legitimately your body's way of telling you that it's not able to process enough energy to function properly, says Amanda Kruse, RD, CD. "In some cases, your body may even go into survival mode as a way of conserving energy stores, because it's not sure when you will feed it next," Kruse says. "The grogginess and associated feelings are your body's way of slowing you down to conserve energy."
Obliterating a whole nutrient category or food group from your diet is just not a good idea. There are a few exceptions to this rule, because certain medical conditions, such as epilepsy, can be controlled by eating an extremely low-carb diet, Harbstreet says. (In fact, the buzzy ketogenic diet was first designed for people with epilepsy.) But those patients would be closely supervised by a dietitian and doctor. Outside of medical necessity, it's not advised to cut carbs completely out of your diet, Kruse says. While cutting carbs may not cause long-term damage physically, it "does untold damage to our relationship with food and continues a cycle of disordered thoughts and behaviours around food," Harbstreet says.
One more time for the people in the back: "It's just unrealistic to think one could subsist on a diet completely devoid of carbohydrates," Harbstreet says. Not to mention, when you decide not to eat carbs, you're also eliminating an enormous number of everyday foods that can deliver important nutrition, she says. If you have carb flu, don't just decide to ride it out, because you don't have to avoid carbs or experience carb flu in order to be healthier. Carbs are probably the one thing that will make you feel better — so raise a croissant to that.
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