Keto flu checklist

Headache, tiredness or cramps in your first days of keto: see what usually helps and which symptoms are not keto flu.

The numbers are estimates for healthy adults and do not replace medical advice or a diagnosis. If you have a condition, take medication, are pregnant or breastfeeding, talk to your doctor first. Read the medical disclaimer.

When to see a doctor

These are not keto flu. If any of the following applies, get medical help; in an emergency call 112 or your local emergency number.

Chest pain or tightness, or a heart beating irregularly or very fast.
Fainting or nearly fainting.
Confusion, trouble speaking or unusual drowsiness.
Vomiting that does not stop, or not being able to keep fluids down.
If you have diabetes (especially type 1): deep and fast breathing, strong thirst, stomach pain, breath that smells fruity.
Symptoms that do not improve after two weeks or get worse.
If you take insulin or other diabetes medication, blood-pressure medication or diuretics: keto may call for a change of dose, so talk to your doctor before you start.

How do you feel?

Tick whatever fits to see what helps. Nothing is sent or saved.

Headache
Usually from losing water and sodium: drink water and add salt to your food, or have a cup of broth a day.
Tiredness, weakness
It is normal in the first days. Broth or salt and good sleep help; for one to two weeks, choose gentle movement over hard training.
Dizziness when standing up
Stand up slowly. Water with salt or broth often helps. If you take blood-pressure medication, talk to your doctor, because it may need adjusting.
Leg cramps
Often from low magnesium or potassium: foods such as spinach, avocado and nuts; no more than 250 mg of magnesium a day from supplements.
Nausea
Smaller meals, eaten slowly, and enough water. If a lot of fat bothers you, increase it gradually.
Constipation
More high-fibre vegetables and more water. Magnesium helps here too.
Irritability, low mood
Usually passes along with the rest. Regular meals with enough protein and fat, so you do not go hungry.
Trouble sleeping
Avoid caffeine after midday and keep a regular bedtime. It usually settles within a few weeks.
Brain fog, trouble concentrating
Usually passes once the body adapts. Water, salt and sleep help.

Why it happens

In the first days of keto the body loses water and sodium as its glycogen stores empty; that is where most symptoms come from. They usually pass within a few days to two weeks.

Sources: Bostock ECS et al., Consumer reports of “keto flu” associated with the ketogenic diet, Front Nutr 2020;7:20 · Phinney SD, Volek JS, The Art and Science of Low Carbohydrate Living (2011).