Core keto rules, the science, electrolytes, and fasting basics — free, and grounded in real science.
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Core rules
Why Net Carbs Are the Number That Matters
Every nutrition label lists “Total Carbohydrate,” but that number lumps together two things your body treats very differently: starches and sugars, which get broken down into glucose, and fiber, which mostly doesn’t.
Fiber is a carbohydrate, but your small intestine lacks the enzymes to break most of it down. It passes through largely intact, doesn’t raise blood glucose the way starch and sugar do, and doesn’t trigger the insulin response that comes with a glucose rise. Some of it gets fermented by gut bacteria further down, but that’s a different process with a different effect on the body than digestion and absorption.
Ketosis depends on keeping insulin low enough, consistently enough, that your body switches to burning fat for fuel instead of glucose. Insulin’s main job is clearing glucose from the blood — so the carbs that matter for staying in ketosis are the ones that actually turn into blood glucose, not the ones sitting on a label under the same “Total Carbohydrate” heading.
That’s what “net carbs” means: total carbohydrate minus fiber. It’s an estimate of the carbohydrate your body can actually use as glucose, and it’s why Ketonaut tracks net carbs against your daily ceiling instead of total carbs — a food with 10g of total carbs and 8g of fiber (like a serving of raspberries) affects your blood sugar nowhere near as much as 10g of total carbs with no fiber (like a serving of white rice), even though both look identical on a “Total Carbohydrate” line.
One thing worth knowing if you read packaging on low-carb products: some brands advertise “net carbs” calculated by also subtracting sugar alcohols, on the reasoning that those affect blood glucose less too. That’s a real, debated effect — but it varies a lot by which sugar alcohol it is, and Ketonaut’s own net carb number only ever subtracts fiber, matching the formula above. If a package’s “net carbs” claim and the number Ketonaut shows for the same food don’t match, trust the app’s calculation — it’s the same formula applied consistently across everything you log, not whatever a given manufacturer chose to advertise.
Educational only — not medical advice. Talk to a doctor before making changes if you have a health condition.
“Macros” just means the three things food calories come from: protein, fat, and carbohydrate. Every diet has some macro split, whether anyone’s counting it or not — keto is unusual mainly because it deliberately caps one of the three.
Carbohydrate is the one keto restricts, and everything else follows from that. Your body’s preferred fuel is glucose, and it keeps blood glucose available either from what you just ate or from glycogen stored in your liver and muscles. Keep carb intake low enough, consistently enough, and glycogen runs low — that’s what pushes your body toward burning fat instead. The carb cap isn’t arbitrary; it’s the one lever that actually determines whether you’re in ketosis at all, which is why Ketonaut tracks it as a hard daily ceiling rather than a rough target.
Protein comes next, and it’s set deliberately rather than left to fill whatever’s left over. Muscle is metabolically expensive to maintain, and a body short on both carbs and protein starts breaking down muscle tissue for fuel — the opposite of what most people want from a diet. Enough protein protects against that. It’s a myth that keto has to mean minimal protein; the diet’s low-carb, not low-protein.
Fat is what’s left. Once your calorie target, protein, and carb ceiling are set, fat fills the remaining calories — that’s the actual reason keto is high-fat, not because fat is doing something special on its own. This is also why “keto” isn’t the same thing as “eat unlimited bacon and butter”: total calories still count, and eating far beyond your target doesn’t stop mattering just because most of those extra calories happen to be fat.
Ketonaut calculates your specific numbers — calories, protein, fat, and your net carb ceiling — from your profile (age, weight, height, activity, goal), using established sports-nutrition formulas rather than a generic ratio. If you’re wondering why your targets look the way they do, that calculation, not a fixed universal ratio, is where the answer lives.
Educational only — not medical advice. Talk to a doctor before making changes if you have a health condition.
Your Protein Range: What the Low, Middle, and High Ends Mean
Your net carb ceiling is one hard number. Your protein target isn’t — Profile → Profile & Goals shows it as a range, with a low end, a high end, and a pinned “ideal” value in between. All three come from the same research, just read at different points along it, and it’s worth knowing what each point is actually optimizing for.
The range itself — 1.6 to 2.2 grams of protein per kilogram of body weight — is the deficit-specific band the International Society of Sports Nutrition cites for protecting muscle while eating in a calorie deficit. That’s narrower, and higher, than ISSN’s broader “sufficient for most exercising individuals” range (which starts around 1.4g/kg), because holding onto muscle while also running a calorie deficit is a harder job than maintenance eating asks of your body, and it takes more protein to do it reliably.
The low end of the range is the floor that research shows reliably protects muscle during a deficit — not a bare-minimum-to-avoid-deficiency number, but not a large buffer above the requirement either. It’s the easiest of the three numbers to hit consistently, which makes it the reasonable place to aim if precision stresses you out more than it helps you, or if you’d rather not plan meals around an exact gram count.
The high end is the same research’s upper bound — extra insurance against muscle loss, and more valuable the larger or longer your calorie deficit runs. It’s also the hardest number to hit day after day, since it usually means deliberately prioritizing protein-dense foods rather than letting protein land wherever it lands. Worth reaching for if maximal protection matters more to you than convenience; not a number to feel behind on if it doesn’t.
The pinned value in the middle is Ketonaut’s default estimate, not a number the app expects you to land on exactly. Landing anywhere between the low and high ends, consistently, is what the range exists to make possible — the real risk zone is spending a lot of time under the low end, not which precise gram count you hit above it. One more thing worth knowing: if you’ve set a goal weight in Profile & Goals and it’s lower than your current weight, the range is calculated from that goal weight instead — deliberately, since the point of the range is protecting the muscle you’ll still have at a lower body weight, not padding the number with fat mass you’re in the middle of losing.
Educational only — not medical advice. Talk to a doctor before making changes if you have a health condition.
Normally, your body runs on glucose. You eat carbs, blood glucose rises, insulin ushers that glucose into cells for immediate use, and whatever’s left over gets stored as glycogen in your liver and muscles for later.
Cut carbs low enough, and that glycogen store starts running down — for most people, somewhere over one to three days of sustained restriction. As glycogen falls and less glucose is coming in, insulin drops too, and that drop is the real signal. Insulin’s other job, besides clearing glucose, is telling fat cells to hold onto their fat. When insulin falls, that brake releases, and stored fat starts getting mobilized in much larger amounts.
Here’s the part that’s specific to ketosis, not just fat-burning in general: your liver takes a portion of that mobilized fat and converts it into three water-soluble molecules called ketone bodies — acetoacetate, beta-hydroxybutyrate, and acetone. Unlike fat itself, ketone bodies travel freely in the blood and can cross into the brain, which normally can’t run on fat directly. That’s the point of the whole mechanism: ketone bodies are a glucose-sparing backup fuel your body can manufacture from its own fat stores once carbs are scarce.
It’s worth clearing up a common source of alarm: nutritional ketosis (what a low-carb diet produces) is not the same thing as diabetic ketoacidosis, a dangerous condition seen in uncontrolled type 1 diabetes. DKA happens when someone has almost no insulin at all — not just low insulin from diet — and ketone levels climb far higher than diet alone ever produces, alongside dangerously high blood glucose. Nutritional ketosis is a normal, bounded metabolic state; DKA is an insulin-deficiency emergency. They share a word, not a mechanism.
Getting here isn’t instant. Most people take a few days to a couple of weeks to feel fully “keto-adapted,” as the body’s enzymes and fuel-handling machinery shift toward burning fat and ketones more efficiently — which is also roughly the window “keto flu” symptoms tend to show up in. And it’s not a permanent switch either: a high enough carb intake on any given day can push glycogen and insulin back up and slow ketone production, which is exactly why Ketonaut’s net carb ceiling is a daily number, not a one-time milestone.
Educational only — not medical advice. Talk to a doctor before making changes if you have a health condition.
If you test both blood glucose and blood ketones, the Glucose Ketone Index — GKI — combines the two readings into a single number that reflects how deep in ketosis you currently are, rather than looking at either one alone.
The formula is glucose divided by ketones, both in mmol/L: GKI = glucose ÷ ketones. Most home glucose meters in the US report mg/dL rather than mmol/L, so if that’s what yours shows, divide the glucose reading by 18 first to convert it before doing the division.
Lower GKI means deeper ketosis, because it means relatively more ketones relative to glucose. Roughly: above 9 is little to no ketosis, 6 to 9 is low-level ketosis, 3 to 6 is moderate ketosis, 1 to 3 is high or therapeutic-level ketosis, and below 1 is the deepest therapeutic range — a range originally studied in metabolic therapy contexts, not something everyday keto eating needs to chase. Most people eating a well-formulated keto diet for general health land somewhere in the moderate range without trying to push lower.
A single GKI reading is easy to misread in isolation, because plenty of things move it besides how well you’re doing at keto. A fasted first-thing-in-the-morning reading is often higher than expected due to the “dawn phenomenon” — a normal cortisol-driven glucose rise that isn’t a sign anything went wrong. A large protein meal can raise glucose somewhat through gluconeogenesis. And anyone taking exogenous ketones (a supplement, not diet) will see an artificially better GKI that reflects the supplement, not dietary progress.
Because reading a GKI well depends on context a single number doesn’t carry with it — how long you’ve been keto, when you last ate, what you last ate, whether you’ve taken exogenous ketones — Ketonaut’s Coach is built to interpret a reading against your actual logged context rather than the bare number. This article is here so the formula and the general shape of the scale aren’t a mystery walking in.
Educational only — not medical advice. Talk to a doctor before making changes if you have a health condition.
The headache, fatigue, muscle cramps, and irritability some people hit in their first week or two of keto have a name — “keto flu” — and a specific, well-understood cause. It isn’t carb withdrawal in some vague sense; it’s electrolytes, and it’s driven by the same insulin drop that produces ketosis in the first place.
Insulin does more than manage blood glucose — it also tells your kidneys to hold onto sodium. When carb intake drops and insulin falls, that signal weakens, and your kidneys start excreting more sodium than usual. Water follows sodium out, and potassium and magnesium get pulled along with that shift too. The net effect, especially in the first couple of weeks before your body adjusts, is a real electrolyte deficit — not dehydration in the simple “drink more water” sense, but a loss of the minerals water needs to actually stay put and do its job.
The fix is deliberately eating and drinking more of these three than pre-keto habits would suggest, since a diet that avoids many typically-salty processed and starchy foods also tends to under-deliver sodium without you noticing. Ballpark daily ranges for someone eating keto: sodium 3,000–5,000mg (above general-population guidance, and that’s intentional here), potassium 3,000–4,000mg, and magnesium 300–500mg from food and supplements combined — though if you’re using a magnesium supplement specifically, keep the supplemental portion under 350mg, which is where NIH’s upper-limit guidance applies (it doesn’t apply to magnesium from food).
Salting food more liberally than feels normal, drinking broth, and using an electrolyte supplement or a pinch of salt in water are the practical version of the numbers above.
One real safety note, not a formality: these higher-than-usual ranges assume normal kidney function. If you have kidney disease, or take blood-pressure medication, ACE inhibitors, ARBs, or potassium-sparing diuretics, potassium in particular carries real risk (hyperkalemia) at these levels — talk to a doctor before deliberately increasing intake, rather than treating the ranges above as universal.
Educational only — not medical advice. Talk to a doctor before making changes if you have a health condition.
Intermittent fasting just means confining eating to a smaller window of the day — 16:8 (an 8-hour eating window) is the most common starting point — rather than not eating for extended stretches. It’s a schedule change, not starvation, and it’s worth being clear about that distinction up front since the two get conflated a lot.
Keto and fasting pair naturally because of what you already do at every meal on keto: keep insulin low. A day of low-carb eating already leaves insulin lower than a typical mixed diet would, which is a big part of why people on keto often find skipping breakfast or pushing lunch later feels easier than it did before — there’s less of an insulin spike to come down from in the first place.
The metabolic process people usually mean when they bring up fasting’s benefits is autophagy — literally “self-eating,” the process by which cells break down and recycle their own damaged or worn-out components. It’s not unique to fasting; it’s running at some background level all the time. What fasting (and the low insulin that comes with it) appears to do is turn that process up. It’s a genuinely active area of research, and the cellular mechanism is well established in lab studies — human-outcome evidence for exactly how much fasting, for how long, produces a meaningful autophagy benefit is still developing, so it’s worth treating specific health claims about fasting with the same caution you’d apply to any actively-researched topic rather than as settled fact.
Fasting isn’t the right call for everyone, and it’s worth saying plainly rather than assuming it applies universally. Pregnancy and breastfeeding, a history of disordered eating, and being on medication that lowers blood glucose (insulin, sulfonylureas) are all real reasons to talk to a doctor before extending a fasting window — the risk in some of these cases isn’t discomfort, it’s a genuine medical complication.
This article covers the concept — Ketonaut doesn’t have a dedicated fasting timer yet, but it’s on the roadmap, and this is the grounding it’ll build on once it exists.
Educational only — not medical advice. Talk to a doctor before making changes if you have a health condition.