Cramps, salt and electrolytes in the first month

The calf cramp that wakes you at four in the morning in week one is the most predictable event in this whole way of eating, and the most easily fixed. It is also the one people blame on the diet when the answer is a quarter teaspoon of salt.

What is actually happening

A cramp is an involuntary contraction of a whole muscle, sustained for seconds to minutes, that hurts. The mechanism is nerve hyperexcitability: the nerve endings that tell muscle fibres to fire become more likely to fire when they are tired, cold, or sitting in fluid that has shifted.

On a low carbohydrate intake, three things push in that direction at once. Insulin falls, and the kidney responds by excreting more sodium. Sodium is the main mineral lost in sweat and the one that holds water in the right places. Water follows the sodium out, so total body water falls too. And the first fortnight is often a period of eating less overall, because appetite drops before you have learned to trust it.

That combination, low sodium and low water, is the commonest cause of night cramps in the first month.

Fix the salt first

A quarter teaspoon of salt in 500ml of water, twice a day, is a reasonable starting point for most adults. Sip it rather than drinking it in one go, and do not drink it on an empty stomach first thing if it makes you feel sick.

Salt on food does the same job and is easier to keep up. Most people eat well under the 6g a day the NHS recommends as a maximum; on a low carbohydrate intake the question is whether you are getting enough rather than whether you are getting too much.

That last point has an exception. If you have high blood pressure, kidney problems, or take medication that affects sodium, adding salt is a conversation with your GP rather than a decision you make from a website. Diuretics in particular change the arithmetic.

Water, properly

Two to 2.5 litres a day, more if it is warm, more if you are training. Pale straw urine is the practical check.

Drinking a large volume of water without sodium does not help and can make things worse, because it dilutes what sodium you have. Water and salt belong together.

Magnesium, honestly

Magnesium is the supplement everyone recommends and the evidence is weaker than the recommendation.

Trials of magnesium for night cramps in older adults have generally found no meaningful reduction in frequency or severity. That does not mean it never helps, and it does mean it is not the fix people describe.

If you want to try it, a pharmacist can advise on a form and dose. Magnesium citrate and oxide pull water into the bowel and loosen stools, which is a predictable side effect and a way of finding your ceiling.

Potassium and calcium get mentioned a lot and are rarely the problem in someone eating meat, which supplies both in quantity.

Quinine, which you should not use

Tonic water contains quinine and has a folk reputation for cramps. The UK regulator's advice is that quinine should not be used for night cramps, because of the risk of serious blood problems, and that includes tonic water as a self-treatment.

It is one of the few things in this area with a clear official answer, and the answer is no.

The things that are not minerals

Cold feet at night. Wear socks.

Unfamiliar exercise, which produces cramps in the muscles you used, usually in the hours afterwards.

Standing on hard floors all day.

Sleeping with the toes pointed, which shortens the calf and makes the cramp more likely. A pillow under the feet to keep the ankles at 90 degrees helps some people.

In the moment

Stand up if you can, and put weight on the leg. Pull the toes towards your shin, hard, and hold it for 30 seconds. That stretches the calf and interrupts the contraction. Then walk around for a minute.

Do not massage it while it is still locked; stretch first.

When it is not a salt problem

Cramp in one calf with swelling, warmth, redness or pain that does not ease with stretching needs urgent medical attention, because a clot in the leg is a different problem and a serious one.

Cramp with weakness, numbness, or that keeps coming back in the same place regardless of salt and water is a GP conversation.

Cramp with palpitations, unusual fatigue, or dizziness that does not settle within a few minutes of standing is also a GP conversation, and worth mentioning that you changed your diet and when.