Keto flu: symptoms, causes and how to feel better fast
6 min read · Reviewed October 18, 2026 · By the KetoSwap team
Why the first week of keto can bring headaches and fatigue — and the simple sodium, potassium and magnesium fixes.
A few days into keto, many people feel tired, foggy and headachy — the so-called "keto flu." The good news: it's usually short-lived, and most of it can be prevented with salt, water and a few electrolyte-rich foods.
Keto flu symptoms
- Headache and brain fog
- Fatigue and low energy, especially during exercise
- Irritability or trouble sleeping
- Dizziness when standing up quickly
- Muscle cramps (often at night) and heart palpitations
- Nausea, cravings and constipation
Why it happens
When you cut carbs, insulin levels fall. Lower insulin signals your kidneys to excrete more sodium — and water follows. You also shed the water stored with glycogen. That rapid fluid and sodium loss (with potassium and magnesium close behind) explains most symptoms. Your brain and muscles are also switching to fat and ketones for fuel, which takes some time.
How to get rid of keto flu fast
- Have salty broth. A cup or two of bone broth or bouillon often relieves a headache within the hour.
- Salt your food generously and add pickles, olives and salted nuts.
- Drink water — thirst can lag behind fluid loss in the first week.
- Eat potassium-rich keto foods: avocado, spinach, mushrooms, salmon.
- Consider magnesium (citrate or glycinate) for cramps and sleep, if your doctor agrees.
- Eat enough. Don't combine a brand-new diet with aggressive calorie cutting; add fat until you feel satisfied.
- Go easy on exercise for a week — light walks rather than hard workouts.
Daily electrolyte targets
| Electrolyte | Common keto guidance | Food sources |
|---|---|---|
| Sodium | 3,000–5,000 mg/day (about 1½–2½ tsp salt total, from all sources) | Salt, broth, pickles, olives, cheese |
| Potassium | 2,600–3,400 mg/day (adequate intake for adults) | Avocado, spinach, salmon, mushrooms, zucchini |
| Magnesium | 310–420 mg/day (RDA for adults) | Pumpkin seeds, almonds, spinach, dark chocolate |
Important: if you have high blood pressure, heart failure or kidney disease — or take diuretics or blood-pressure medication — ask your doctor before increasing salt or taking potassium or magnesium supplements.
Prevent it next time
Start salting and hydrating on day one rather than waiting for symptoms. Some people prefer to cut carbs gradually over a week or two instead of all at once. Our 7-day meal plan includes salty, satisfying meals to ease the transition.
Homemade Electrolyte Limeade
Bulletproof-Style Butter Coffee
Egg Drop Soup
Avocado Baked Eggs
When to see a doctor
Keto flu should be mild and short. Seek medical care for persistent vomiting, confusion, fainting, chest pain, a very fast or irregular heartbeat, signs of dehydration that don't improve, or any fever. If you take insulin or other glucose-lowering drugs, talk to your care team before starting — low blood sugar can mimic or worsen these symptoms.
Frequently asked questions
How long does keto flu last?
Usually a few days to a week, starting 2–3 days after cutting carbs. With enough salt and fluids many people barely notice it.
Is keto flu a real flu?
No — it isn't an infection and isn't contagious. It's a cluster of symptoms from fluid and electrolyte shifts as your body adapts to low carb intake. A fever is not keto flu; see a doctor.
Will carbs fix keto flu?
Eating carbs would ease it, but you'd restart adaptation. Salt, water and magnesium usually work within an hour or two.
This guide is general information, not medical advice. Talk to your doctor before starting keto — especially if you take medication for diabetes or blood pressure, are pregnant or breastfeeding, or have kidney, liver or gallbladder disease.