If you've landed here mid-headache, mid-fog, mid-wondering-whether-this-was- a-mistake — first thing: drink a glass of water with half a teaspoon of salt stirred into it. Properly stirred. Then come back to this page.

Most of what people call "keto flu" isn't keto at all. It's the body responding to the loss of sodium and other minerals that follow when insulin drops and the kidneys start flushing water differently. The carbohydrate restriction is real and the metabolic adaptation is real, but the symptoms — the headache, the fatigue, the light-headedness, the mild irritability — are nearly always a mineral problem. They're also nearly always fixable in about an hour, not in the two weeks you've been told to wait out.

This page is what's actually happening and what to do about it.

What "keto flu" actually is

A cluster of symptoms that show up in the first week or two of keto, most acute around days two to five: fatigue, headache, dizziness, weakness, sometimes irritability or muscle cramps, occasionally heart palpitations. The phrase "keto flu" became standard because the cluster feels like flu — heavy, foggy, drained — but it isn't an illness in any meaningful sense. There's no virus. The body isn't fighting anything. It's just running short on something it didn't know it would need this much of.

What it's running short on is sodium, mostly. Sometimes potassium. Often magnesium too. The fix is to replace what you've lost, in roughly the right proportions, and the symptoms usually settle within an hour of the first serious replenishment.

The reason this isn't obvious — even to people who've done keto multiple times — is that the standard cultural advice about salt has been wrong for the keto context for decades. Most people grew up being told to eat less salt. On keto, you need to eat substantially more. The intuitions that served you on a standard diet are working against you here.

Why it happens

Worth understanding the mechanism, because it explains why the fix is so specific.

In your normal eating pattern, your insulin level stays elevated through most of the day. Insulin does many things, but one of them is signalling the kidneys to hold onto sodium. As long as insulin is high, sodium stays in your blood.

When you cut carbohydrates and insulin drops, that signal goes away. The kidneys, freed from holding onto sodium, start excreting it — along with the water that came with it. People can lose three to five pounds of water in the first week of keto, which is most of what early "weight loss" actually is. The water is going out, and the sodium and potassium are going out with it.

This is fine if you replace them. It's brutal if you don't. The headache is mild dehydration plus low sodium. The fatigue is reduced blood volume (less water means less blood). The dizziness on standing is the same — your blood pressure can't quickly compensate when there's less volume to work with. The cramps are low potassium or magnesium. The irritability is mostly the fatigue, with a side of low blood sugar your body hasn't quite learned to ride out yet.

None of this is a sign keto is wrong for you. It's a sign your body is adjusting and you haven't given it enough of the minerals it now needs in higher quantities. The adjustment is meant to happen; the deficiency isn't.

The fix isn't to wait it out. The fix is to replenish.

The three minerals that matter

In rough order of importance on keto: sodium, potassium, magnesium. All three matter. The proportions and the specific advice differ.

Sodium — 3 to 5 grams a day

The most important and the most counterintuitive. Most public health messaging treats sodium as something to limit. On keto, with insulin lower and kidneys excreting more, you actively need more of it.

Three to five grams of sodium a day is the target for most adults on keto. A teaspoon of table salt is about two grams of sodium, so you're aiming for the equivalent of one and a half to two and a half teaspoons of salt a day, total — including what's already in your food. People who sweat heavily, or live in hot climates, or are also intermittent fasting, need the upper end.

Practical sources:

If you're worried about salt for cardiovascular reasons — and many people are, after decades of public health messaging — the recent evidence is nuanced. For most healthy adults, sodium intake in the 3-5g range isn't harmful and is actively necessary on keto. If you have hypertension, heart failure, or kidney disease, talk to your doctor; the targets are different.

Potassium — 3,000 to 4,000 mg a day

Harder to hit than sodium, because most high-potassium foods are also high-carb (bananas, potatoes). You have to be more deliberate about it.

The good keto-friendly sources:

A balanced keto plate with a fatty fish, two handfuls of cooked greens, half an avocado, and some mushrooms hits most of a day's potassium in a single meal. Doing this consistently is more reliable than supplementing.

If you do supplement, lite salt (a mix of sodium chloride and potassium chloride sold in most supermarkets) is a useful single addition — it raises both sodium and potassium at the same time. Standalone potassium supplements come in small doses for a reason (too-high potassium can be dangerous for the heart); stick with food sources and lite salt unless your doctor tells you otherwise.

Magnesium — 300 to 400 mg a day

The mineral most people are deficient in regardless of whether they're doing keto. Modern soils are depleted; modern diets are too. On keto, the deficiency tends to be more noticeable because of the higher turnover, and the symptoms — muscle cramps, restless sleep, occasional heart palpitations — are easy to misattribute to keto when they're really magnesium.

Food sources are limited but useful:

For most people, supplementing is easier than getting magnesium fully from food. The form matters:

A daily magnesium supplement at night is one of the single best low-cost habits for anyone on keto. The improved sleep alone tends to be obvious within a week.

The Reset Card baseline

If you only do four things to prevent or fix keto flu:

  1. Salt your food generously at every meal — more than feels normal to you
  2. Drink salted water on waking — half a teaspoon of salt in a large glass of water, before coffee or anything else
  3. Eat one high-potassium food at every meal — avocado, leafy greens, fatty fish, or salmon
  4. Take 200-400 mg of magnesium glycinate or citrate at night

This is the Reset Card's electrolyte section in essence. The Reset Card itself is a one-page printable with the daily targets, the foods, and a checklist — pinned up on the fridge in week one, it prevents most of the "why do I feel terrible" questions. Download the Reset Card from the site if you don't have it yet.

The book has the same protocol with more detail and the daily structure that integrates it into the wider rhythm — but for the immediate question of "why do I feel rough this week," the Card is what you want on the fridge.

Signs you've got it right

You should feel meaningfully better within 24 to 48 hours of getting the electrolytes right. Specifically:

If all of these are true by day 7 or 8, your electrolytes are sorted. The remaining work of keto adaptation happens quietly in the background and doesn't generally produce dramatic symptoms.

Signs you've got it wrong

If you're past day 10 and still feel rough, work down this list:

Persistent fatigue or brain fog. Almost always under-salting. Most people who think they're getting "enough" salt are getting half of what they need. Try doubling your salt intake for three days and see what happens. If the fatigue lifts, that was the issue.

Muscle cramps. Magnesium first, potassium second. If you're not taking a magnesium supplement yet, start. If you are and you're still cramping, look at potassium — are you eating an avocado a day? Leafy greens at most meals?

Heart palpitations. Worth being precise here. Occasional, brief flutters in the first week are usually electrolytes — most commonly potassium. Persistent or alarming palpitations are not something to manage with diet alone; see a doctor. This is especially true if you're on any medication that affects the heart or kidneys.

Headaches that don't respond to salt water. Rare, but check hydration first (water with salt, not just water — salt without water or water without salt are both incomplete). If that doesn't help within an hour, see a doctor; persistent unexplained headaches are worth investigating regardless of diet.

Light-headedness on standing past week 2. Probably still under- hydrated or under-salted. Could also be a sign you're under-eating overall — keto isn't a calorie-restriction protocol; eat satisfying meals.

Special considerations

A few cases where the standard advice needs adjustment.

Blood pressure medication. If you take medication for hypertension, talk to your doctor before significantly increasing sodium. Keto can sometimes lower blood pressure on its own; combined with higher salt intake, the interaction matters. This isn't a reason to avoid keto — many people on blood pressure medication do well on it and end up reducing dosages with their doctor's guidance — but it's a reason to involve them.

Kidney disease. Anyone with diagnosed kidney issues should treat electrolyte protocols cautiously and work with their nephrologist. Potassium especially needs medical guidance in CKD.

Diuretics. Some medications (including some blood pressure drugs and some antidepressants) increase electrolyte loss further. The combination with keto can be sharp. Doctor.

Athletes who sweat heavily. You need more sodium than the 3-5g range. Endurance athletes in summer training can need 7-10g a day, sometimes more. Salt your training drinks; eat salty snacks during long sessions.

Hot climates. Same logic. If you're in a hot country and sweating through your clothes daily, your sodium need is higher. Move toward the upper end of the range and don't ration.

Intermittent fasting on top of keto. Amplifies the electrolyte demand because you're not getting any incoming minerals during the fasting window. Make sure the eating window includes adequate salt and potassium, and consider salted water during the fast.

A closing word

Most of what makes keto feel difficult in the first weeks is fixable in about an hour, with about thirty pence of salt. The minerals are the single most under-discussed piece of low-carb eating, and they're the piece that converts "I can't do keto" into "this feels manageable" for the largest number of people.

The Reset Card has all of this on one printable sheet — daily targets, food sources, the morning salt-water habit, the evening magnesium. Download it free at ketodive.life if you don't have it yet. Pin it on the fridge for the first month.

The book has the longer protocol and the explanation of how electrolytes fit into the wider five-phase journey. Keto Dive on Amazon is where to find it.

And if you're reading this because you tried keto, felt rough, and quit — that wasn't keto. That was electrolytes. The next attempt with this piece sorted tends to feel different from the first. How to restart keto without the guilt is the next thing to read.