About 24 hours into the ketogenic diet, I began to get cranky. This was a crankiness beyond my usual slightly irritated (OK, very irritated) demeanor when I'm hungry. I was tired, starving, headachey, craving carbs, and on the verge of tears. When you embark on a keto diet — which involves eating lots of healthy fats, a moderate amount of protein, and very few carbs — it's actually pretty normal. It's even got a nickname: the keto flu.
"If you follow the ketogenic diet, you reduce your carbohydrate intake to extremely low levels," Michelle Routhenstein, MS, RD, CDE, CDN, the owner of Entirely Nourished, a nutrition counseling and consulting private practice, tells POPSUGAR. "The body then has to adapt to break down fat for energy instead of using glucose, the primary fuel your brain is used to using to survive." She explains that your body can convert carbs to usable energy pretty easily, but it takes your body a few extra steps to use fat and protein as fuel. "Since fat is usually reserved as a secondary fuel, the body has to adapt to the shock and 'withdrawal' of its usual source of energy, which can lead to flulike symptoms," she says.
She tells POPSUGAR that the keto flu can last anywhere from three to seven days, though not everyone will experience symptoms. "It depends on the overall health and nutritional status of the individual before starting the ketogenic diet," she says. "Nutrient deficiencies, age, activity level, sleep, stress, hydration status, and prior carbohydrate intake (including the amount and consumption of complex and/or simple) can all impact if and how severe the keto flu may be."
Note: "People with certain medical conditions such as diabetes or kidney disease should be monitored closely by a doctor prior to starting the ketogenic diet, as there can be dangerous reactions to ketosis," Routhenstein says.
Here are the common symptoms of the keto flu:
- Low energy
- Brain fog
- Muscle cramps
- Moodiness or irritability
- Bad breath
- Loss of appetite
- Poor concentration
- Stomach pain
- Muscle soreness
- Low libido
- Difficulty sleeping
- Sugar cravings
To help make the keto flu less terrible, there are a few things you can do. First off, increase the amount of water you drink. Routhenstein recommends at least two to three liters of water per day. "When carbohydrates are reduced, carbohydrate storage (glycogen levels) dips to low levels, and since carbohydrates hold onto water, water is excreted more from the body," she explains. Basically, that means you'll get dehydrated, so it's really important to drink water.
Also, stick to light exercise while you're experiencing the keto flu. "Exercise uses more fuel (primarily glucose), and since glucose is being severely reduced, avoiding intense exercise can assist with the new transition," Routhenstein explains.
Because the keto diet is quite restrictive, it's easy to miss out on essential nutrients — especially potassium, calcium, B vitamins, and magnesium. "Some individuals may become sodium deficient because when insulin levels are kept low (due to low carbohydrate intake), the kidneys excrete sodium at a higher rate," Routhenstein explains. Being nutrient deficient can cause many of the keto flu symptoms. She recommends incorporating lots of green leafy vegetables, almonds, and avocado into your diet.
Routhenstein also says that slowly transitioning to a keto diet can also help minimize the symptoms of the keto flu.