Two or three days into cutting carbohydrate, almost everybody wants the same reassurance: is this working yet? The instinct is to buy something that will tell you — strips, a breath meter, a blood monitor and a box of lancets.
You do not need any of it. Ketosis announces itself fairly clearly if you know what you are listening for, and the signals that matter most are the ones no device measures.
The reliable signs
Thirst, and a great deal more time in the bathroom
The first and least glamorous. As insulin falls, your kidneys let go of sodium and the water it was holding, and you spend the first two or three days losing fluid faster than usual. Dry mouth, frequent trips, and a scale that drops in a way no fat loss could account for. It is not fat. It is your glycogen stores emptying, and each gram of glycogen takes about three grams of water with it.
This one is so reliable it is almost diagnostic — and it is also the reason the first week can feel rough. If it does, that is the keto flu, and it is a salt problem with a same-day fix.
A metallic or faintly fruity taste, and breath to match
Acetone is one of the three ketone bodies, it is volatile, and some of it leaves through your lungs. The result is a taste people describe as metallic, fruity, or oddly like nail varnish remover — which is accurate, because acetone is what is in nail varnish remover.
It is a genuine sign that you are producing ketones. It is a poor gauge of anything else: it usually appears in the first week or two and then fades as your body gets better at using what it makes. Its disappearance is not a problem.
Appetite quietening down
The most useful sign on the list, and the one people notice with the most surprise. Not the absence of hunger, but a change in its character: it stops arriving as an urgent two-hourly interruption and becomes something closer to information. Meals become easier to postpone. The biscuit tin stops broadcasting.
If this has happened, something real has changed, whatever a strip says.
The afternoon holds
The three o'clock trough is a blood-sugar phenomenon. When your energy stops depending so tightly on the last thing you ate, the trough flattens. People usually notice this in week two, and often describe it before they describe anything else as evidence that the approach is doing something.
Sleep changes, briefly, then settles
Some people sleep less deeply for the first week or so, or wake at four in the morning for no reason they can name. It usually resolves as electrolytes come right. If it does not, magnesium in the evening is the standard first move.
An important distinction
Everything above describes nutritional ketosis — mild, controlled, and normal in anyone eating this way. It is not the same thing as diabetic ketoacidosis (DKA), a medical emergency in which ketones and blood sugar are both dangerously high, almost always in people with type 1 diabetes (and occasionally type 2 on certain medications, notably SGLT2 inhibitors).
The distinction matters here because the early signs overlap: intense thirst, frequent urination and fruity breath appear on both lists. What separates them is company and severity — DKA brings nausea or vomiting, stomach pain, laboured breathing, confusion, and it worsens over hours rather than settling. If you have type 1 diabetes, ketogenic eating needs your diabetes team involved from the start, not this page. If anyone develops those symptoms together, that is an emergency department, not an electrolyte drink.
The signs that mislead
Urine strips fading
The single most common false alarm. Strips measure acetoacetate that you are excreting — in other words, what you did not use. As you become better adapted, you waste less, and the strips go pale. Enormous numbers of people conclude they have fallen out of ketosis at exactly the point their body started working properly, and either restrict further or give up.
Strips are mildly useful in week one to confirm you have crossed the line. After that they mostly measure your hydration.
The scale
Week one's dramatic drop is water and week three's silence is not failure. Body weight moves several pounds a day on fluid, salt, glycogen and the ordinary business of digestion, and for anyone who menstruates it moves predictably across the month too. A scale is a noisy instrument being read daily as though it were a precise one.
Feeling terrible
There is a persistent idea that the worse you feel, the more it must be working. It is exactly backwards. Feeling rotten in week one usually means you are short of sodium, short of food, or both. Adaptation does not require suffering, and suffering is not evidence of progress.
If you do want to measure
No judgement — some people find a number genuinely settles their mind. What each one actually tells you:
- Urine strips. Cheap. Useful for a week, then misleading. Sensitive to how much water you have drunk.
- Breath meters. Measure acetone, no consumables, reusable. A reasonable middle option; readings track trends rather than precise levels.
- Blood meters. The accurate one, and the one with ongoing costs and lancets. Nutritional ketosis is usually quoted as roughly 0.5 to 3.0 mmol/L. Worth knowing that a lower reading at week eight than week two can mean better uptake, not less production — the same trap as the strips, in more expensive form.
The honest caveat: none of these measure whether the approach is working for you. They measure whether ketones are present. Those are different questions, and the second one is answered by your energy, your appetite and whether you can imagine still doing this in six months.
How deep is deep enough?
There is a common belief that higher ketone readings mean better results. For weight loss and everyday energy, there is no good evidence for it. Above the threshold, more is not better — it usually just means you have eaten less, and occasionally that you have eaten too little.
The exceptions are therapeutic: ketogenic protocols for epilepsy and certain neurological and metabolic conditions do target specific ranges, and those are run under medical supervision for good reason. If that is your situation, your clinician's numbers are the ones that matter, not a website's.
What to watch instead
If you want one set of markers to judge the first six weeks by, use these. They cost nothing and they are far better predictors of whether this will still be part of your life next year:
- Is hunger quieter and more predictable than it was a month ago?
- Does the afternoon hold?
- Can you miss a meal without it becoming an event?
- Are you sleeping at least as well as before?
- Could you describe what you ate yesterday without checking, and would you be happy to eat it again tomorrow?
Four or five yesses and you are fine, whatever the strip says. Two or fewer, and the problem is usually structural rather than metabolic — not enough salt, not enough food, or a plan built on willpower rather than rhythm.
You stop negotiating with hunger.
Where this fits
In Keto Dive, measurement is deliberately kept in its place. The book's position — argued at more length than a web page allows — is that tracking is optional, and that the anchors do the work: two meals at settled times, adequate protein, enough salt, and a carbohydrate ceiling low enough to stay under without arithmetic.
If you are early enough to still be feeling rough, read the keto flu guide first. If you are past that and wondering when the promised steadiness arrives, that is fat adaptation, and it runs on a longer clock than ketosis does.
This guide is general information, written to accompany a book, and is not medical advice. Everyone's health context is different — medication, pregnancy, diabetes, kidney or heart conditions, and a history of disordered eating all change what is sensible. Before making significant changes to how you eat, particularly if any of those apply, talk to your GP or a registered dietitian.